Transcriber Note

Text emphasis denoted by =Bold= and _Italics_.




     +---------------------------------------------------------+
     |                     UNITED STATES                       |
     |               DEPARTMENT OF AGRICULTURE                 |
     |                                                         |
     |                    CIRCULAR No. 363                     |
     |                                                         |
     +---------------------------------------------------------+
     | Washington, D. C.                          October 1935 |
     +---------------------------------------------------------+
     |                                                         |
     |                                                         |
     |                     THE MIGRATION                       |
     |                  OF NORTH AMERICAN BIRDS                |
     |                                                         |
     |                                                         |
     |                           By                            |
     |                 FREDERICK C. LINCOLN                    |
     |                                                         |
     |  Senior Biologist in Charge, Section of Distribution    |
     |  and Migration of Birds Division of Wildlife Research,  |
     |            Bureau of Biological Survey                  |
     |                                                         |
     |                                                         |
     |                     [Illustration]                      |
     |                                                         |
     |                                                         |
     +---------------------------------------------------------+

            For sale by the Superintendent of Documents.
                 Washington, D. C. -- Price 10 cents




           CIRCULAR No. 363                   OCTOBER 1935
               UNITED STATES DEPARTMENT OF AGRICULTURE
                          WASHINGTON, D.C.



              THE MIGRATION OF NORTH AMERICAN BIRDS[1]


        By Frederick C. Lincoln, _senior biologist, in charge
           Section of Distribution and Migration of Birds,
                   Division of Wildlife Research,
                    Bureau of Biological Survey_


[Footnote 1: This circular supersedes Department Bulletin 185, Bird
Migration, by Wells W. Cooke, published in 1915. In addition to his
own original investigations in the field and those reflected in the
files of the Biological Survey, the author has made free use of the
writings of Professor Cooke, Alexander Wetmore, William Rowan, A.
Landsborough Thomson, H. A. Allard, and others. To all these grateful
acknowledgment is made, particularly to Doctor Wetmore, Assistant
Secretary of the Smithsonian Institution, who has read the entire
manuscript and made many valuable comments and suggestions.]




CONTENTS


                                                        Page

  Introduction                                             1

  Mystery of migration                                     3
    Historical accounts                                    3
    Advantages of migration                                4
    Theories of causes of migration                        5

  When birds migrate                                       7
    Movements of species and groups                        8
    Nocturnal and diurnal migration                       11

  How birds migrate                                       13
    Speed of flight andspeed of migration                 13
    Altitudes at which birds travel                       22
    Orientation                                           23
    Segregation during migration                          25

  Where birds migrate                                     27
    Distances of migration vary                           27
    Short and undetermined migration                      27
    Variable migrations wi thin species                   28
    Fall flights not far south of breeding ranges         29
    Long-distance migrations                              30

  Routes of migration                                     33
    Wide and narrow migration lanes                       34
    Atlantic oceanic route                                39
    Atlantic coast route and tributaries                  42
    Mackenzie Valley-Great Lakes-Mississippi Valley
      route and tributaries                               45
    Pacific coast route                                   47
    Pacific oceanic route                                 49
    Arctic routes                                         52

  Evolution of migration routes                           52

  Vertical migration                                      55

  Vagrant migration                                       55

  Perils of migration                                     56
    Storms                                                56
    Aerial obstructions                                   57
    Exhaustion                                            59

  Influence of the weather on migration                   59

  Problems of migration                                   61
    Banding studies                                       61
    Movements of residents                                62
    Migration of the white-throated sparrow               63
    Migration of the yellow-billed loon                   63

  Conclusions                                             65

  Bibliography                                            66

  Index                                                   69




=INTRODUCTION=


Where do the birds go each fall that have nested in our dooryards and
frequented the neighboring woods, hills, and marshes? Will the same
ones return again to their former haunts next spring? What dangers do
they face on their round-trip flight and in their winter homes? These
and other questions on the migratory habits of birds puzzle the minds
of many who are interested in the feathered species, whether it be
the farmer who profits by their tireless warfare against the weed and
insect pests of his crops, the bird student who enjoys an abundance
and variety of feathered inhabitants about him, or the hunter who
wants a continuation from year to year of the sport of wild-fowling.
Lack of information on the subject may mean the loss of an important
resource by unconsciously letting it slip from us. Ignorance of
the facts may be responsible for inadequate legal protection for
such species as may urgently need it. More general knowledge on the
subject will aid in the perpetuation of the various migrants, the
seasonal habitats of some of which are in grave danger from man's
utilization, sometimes unwisely, of the marsh, water, and other areas
they formerly frequented.

The migrations of birds were probably among the first natural
phenomena to attract the attention and intrigue the imagination of
man. Recorded observations on the subject date back nearly 3,000
years, to the times of Hesiod, Homer, Herodotus, Aristotle, and
others. In the Bible are several references to the periodic movements
of birds, as in the book of Job (39:26), where the inquiry is made:
"Doth the hawk fly by Thy wisdom and stretch her wings toward the
south?" Jeremiah (8:7), wrote: "The stork in the heavens knoweth
her appointed time; and the turtle [dove], and the crane, and the
swallow, observe the time of their coming." And the flight of quail
that saved the Israelites from starvation in their wanderings in the
wilderness of Sinai is now recognized as a vast movement of migratory
quail (_Coturnix coturnix_) between their breeding grounds and their
winter home in Africa.

Throughout the ages the return flights of migratory birds have been
important (1) as a source of food after a lean winter, and (2) as the
harbinger of a change in season. The arrival of certain species has
been heralded with appropriate ceremonies in many lands, and among
Eskimo and other tribes the phenomenon to this day is the accepted
sign of the imminence of spring and of warmer weather. The pioneer
fur traders in Alaska and Canada offered rewards to the Indian or
Eskimo who saw the first goose of the spring, and all joined in
jubilant welcome to the newcomer.

Always hunted for food, the large flocks of ducks and geese became
objects of the enthusiastic attention of an increasing army of
sportsmen as the North American Continent became ever more thickly
settled. Most of the nongame species were found to be valuable also
as allies of the farmer in his never-ending warfare against weed
and insect pests. The need for laws protecting the valuable game
and nongame birds and for regulated hunting of the diminishing game
species followed as a natural course. In the management of this
wildlife resource it has become obvious that continuous studies
must be made of the food habits of the various species, their
environmental needs, and their travels. Hence bird investigations
are made by the Biological Survey, the Bureau charged by Congress
under the Migratory Bird Treaty Act with the duty of protecting those
species that in their yearly journeys pass back and forth between the
United States and Canada.

For half a century the Biological Survey has been collecting data on
the interesting and important phenomenon of the migration of North
American birds. The field men of the Bureau have gathered information
concerning the distribution and seasonal movements of the different
species in many extended areas, from the Arctic coast south to the
pampas of Argentina. Supplementing these investigations is the work
of hundreds of volunteer ornithologists and bird students throughout
the United States and Canada, who each year, spring and fall, forward
to the Bureau reports on migrations observed in their respective
localities. Added, to the mass of data thus assembled is a rapidly
growing file of records of birds that have been banded and of the
subsequent recovery of the marked individuals.

These data, together with other carded records gleaned by the
Biological Survey from a vast literature, constitute a series of
files that now contain well over 2,500,000 entries, easily the
greatest existing accumulation of information pertaining to the
distribution and movements of North American birds. Not only do the
facts thus assembled form the basis of regulatory action for the
protection of the birds, but they also make it possible to publish
scientific accounts of the ranges and migrations of the different
species. They furnish the basis of this publication.

The several important bird-protective measures adopted by State and
Federal Governments, particularly those having as their objective the
conservation of the migratory song, insectivorous, and game species,
can be effective only if they have intelligent public support. To
increase such support, information must be more generally available
on that little understood but universally fascinating subject of bird
migration. A brief presentation of facts on the migratory habits
of the birds, scientifically gathered by the Bureau of Biological
Survey over many years, will be helpful to bird-study classes, to
conservation organizations, and to farmers and others individually
interested in the welfare of the birds.




=THE MYSTERY OF MIGRATION=


HISTORICAL ACCOUNTS

Of observers whose writings are extant, Aristotle, naturalist and
philosopher of ancient Greece, was one of the first to discuss the
subject of bird migration. He noted that cranes traveled from the
steppes of Scythia to the marshes at the headwaters of the Nile,
and that pelicans, geese, swans, rails, doves, and many other
birds likewise passed to warmer regions to spend the winter. In
the earliest years of the Christian era, the elder Pliny, Roman
naturalist, in his Historia Naturalis, repeated much of what
Aristotle had said on migration, and added comments of his own
concerning the movements of the European blackbird, the starling, and
the thrushes.

In spite of the keen perception shown in some of his statements,
Aristotle also sponsored some superstitions on bird migration that
persisted for several centuries. One of these, that of hibernation,
became so firmly rooted that in 1878, the American ornithologist
Coues (_20_)[2] listed the titles of no less than 182 papers dealing
with the hibernation of swallows (Hirundinidae). The hibernation
theory accounted for the autumnal disappearance of certain species
of birds as their passing the cold season in a torpid state, hidden
in hollow trees, caves, or the mud of marshes. Aristotle ascribed
hibernation not only to swallows but also to storks, kites, doves,
and others. Some early naturalists wrote fantastic accounts of flocks
of swallows seen congregating in the marshes until their accumulated
weight bent into the water the reeds on which they clung and thus
submerged the birds. It was even recorded that when fishermen in
northern waters drew up their nets they sometimes had a mixed "catch"
purported to consist of fish and hibernating swallows. Clarke (_4_)
quotes Olaus Magnus, Archbishop of Upsala, who in 1555 published a
work entitled "Historia de Gentibus Septentrionalibus et Natura",
wherein he observed that if swallows so caught were taken into a warm
room they soon begin to fly about but would live only a short time.

[Footnote 2: Ttalic numbers in parentheses refer to the Bibliography,
p. 66.]

The hibernation theory survived for more than 2,000 years and is
still occasionally repeated by credulous persons to account for
failure to locate definitely the winter home of the chimney swifts
(_Chaetura pelagica_), which each autumn gather in immense flocks in
southern Georgia and northern Florida and then suddenly disappear.
Thereare, however, records of occurrence during migration for a
few points in the West Indies, Mexico, and Central America, and it
is probable that these birds spend the winter season in the great
rain-forest area of the Amazon Valley in Brazil, passing most of the
daytime high in the air with other swifts that are local residents.

Aristotle was also the originator of the theory of transmutation,
basing it upon the fact that frequently one species will arrive
from the north just as another species departs for more southerly
latitudes. From this he reasoned that although it was commonly
believed that such birds were of two different species, there really
was only one, and that this one assumed the different plumages to
correspond with the summer and winter seasons.

Probably the most remarkable theory that has been advanced to account
for migration is contained in a pamphlet mentioned by Clarke (_4, v.
1, pp. 9-11_), as published in 1703 under the title: "An Essay Toward
the Probable Solution of this Question: Whence Come the Stork and
the Turtle, the Crane, and the Swallow, when they Know and Observe
the Appointed Time of their Coming." It was written "By a Person of
Learning and Piety", whose "probable solution" was that migratory
birds flew to the moon and there spent the winter.

Some who easily accepted the disappearance of the larger birds
as migratory travelers were unable to understand how the smaller
species, some of them notoriously poor fliers, could make similar
journeys. They contended that the larger species, as the storks
and cranes, carried their smaller companions as living freight. In
some of the Mediterranean countries it is still believed that these
broad-pinioned birds serve as aerial transports for the hosts of
small birds that congregate on the shores of the Mediterranean Sea,
awaiting opportunity for this kind of passage to their winter homes
in Africa. Similar beliefs are found among some tribes of North
American Indians.


ADVANTAGES OF MIGRATION

Before presenting some of the present theories concerning the
origin of bird migration, it seems well to consider briefly the
ends served by this annual round trip between breeding grounds and
winter quarters. It is apparent that the migratory habit enables a
species to enjoy the summers of northern latitudes while avoiding
the severity of the winters. In other words, migration makes it
possible for some species to inhabit two different areas at seasons
when each presents favorable conditions. In the performance of its
reproductive duties every pair of birds requires a certain domain,
the extent of which varies greatly in different species. Generally,
however, this territory must be large enough to provide adquate food,
not only for the parent birds but also for the lusty appetites that
come into being with the hatching of the eggs. Thus, if all birds
were to remain constantly either in tropical or in temperate regions,
there might be intolerable overcrowding during the breeding season.
By the spring withdrawal to regions uninhabitable earlier in the
year, the migrants are assured of adequate space and ample food
upon their arrival in the winter-freed North, and it may be assumed
that nonmigrant species resident in the South are benefited by the
withdrawal of the migrants.

Nevertheless it cannot be said that the winter or summer areas are
entirely unsuited to the requirements of every migrating species at
other seasons, for some individuals pass the winter in areas that
are frequented only in summer by other individuals of their species.
The extensive breeding ranges of such species present wide climatic
variations, so that some individuals may actually be resident in a
region where others of their kind are present only in winter.

The tendency in many species to move southward at the approach of
winter is not always due to the seasonal low temperatures, since
experiments have demonstrated that many summer insect feeders, when
confined in outdoor aviaries, comfortably withstand temperatures
far below zero. The main consideration is the depletion of the food
supply, caused either by disappearance or hibernation of insects,
or by the mantle of snow or ice that prevents access to the seeds
and other forms of food found on or close to the ground or submerged
in water. Possibly also the shortened hours of daylight materially
restrict the ability of the birds to obtain sufficient food at a time
when the cold requires an increased supply to maintain body heat. It
is noteworthy that chickadees (_Penthestes atricapillus_) and some
other of our smaller birds have no fear of Arctic weather, as their
food supplies are mainly arboreal and so are always available. Also,
when there is a good supply of food in the form of pine seeds in
Canadian woods, nuthatches (Sitta carolinensis and S. canadensis)
and crossbills (_Loxia curvirostra_ and _L. leucoptera_) will remain
through the winter. When these birds appear abundantly in winter at
points in southern latitudes, it may be concluded that there is a
shortage of their food in the North, or that they have been lured
farther south by the greater abundance of this food there.


THEORIES OF THE CAUSES OF MIGRATION

Migration has long since become a definite hereditary habit that
recurs in annual cycles, probably because of physiological stimuli
associated with the reproductive period. In seeking its origin it
is necessary to study the history of the birds' occupation of their
present ranges, and from the information available to consider what
appear to be reasonable theories. The two now most commonly accepted
are diametrically opposed to each other.

NORTHERN ANCESTRAL HOME THEORY

According to one of these, nonmigratory birds swarmed over the
entire Northern Hemisphere in earlier ages, the conditions of food
and habitat being such as to permit them to remain in their haunts
throughout the year. The entire northern area then afforded the two
important avian requirements--suitable breeding conditions and a
year-long food supply. This is the condition today in the Tropics,
and it is noteworthy that many tropical birds are nonmigratory.
Gradually, however, in the Northern Hemisphere the glacial ice fields
advanced southward, forcing the birds before them, until finally
all bird life was concentrated in southern latitudes. As the ages
passed and the ice cap gradually retreated, each spring the birds
endeavored to return to their ancestral homes in the North, only to
be again driven south at the approach of winter. As the size of the
ice-covered area diminished, the journeys made became ever longer,
until eventually the habits of migration were fixed to accord with
the climatic conditions of the present age.

Thus, this theory supposes that today migratory birds follow the
path of a great racial movement that took place in a distant past,
associated with advances and recessions of the ice. The actions of
the birds themselves lend some support to this theory, as every bird
student has noted the feverish impatience with which certain species
push northward in spring, sometimes advancing so rapidly upon the
heels of winter as to perish in great numbers when overtaken by late
storms. It is probable, however, that at that season the reproductive
impulse urges the birds on to their northern breeding grounds.

SOUTHERN ANCESTRAL HOME THEORY

The opposing theory is simpler in some respects and supposes that
the ancestral home of all birds was in the Tropics and that as all
bird life tends to overpopulation there was a constant effort to
seek breeding grounds where competition would be less keen. Species
that strove for more northern latitudes would be kept in check by
the ice and forced to return southward with the recurrence of winter
conditions. As the ice retreated, vast areas of virgin country became
successively suitable for summer occupancy, but the winter habitat
remained the home to which the birds returned after the nesting
season. It is a fact that some species spend very little time on
their breeding grounds; the orchard oriole (_Icterus spurius_),
for example, spends only 2½ months in its summer home, arriving in
southern Pennsylvania about the first week in May and leaving by the
middle of July.

Both theories assume that migration is an ingrained habit, but
neither is supported by positive biological data. Both have been
criticized also on geological grounds, and neither can be accepted
without qualification. It is apparent, however, that whether the
ancestral home of any species was at the northern or at the southern
limits of its present range, or even in some intermediate region,
the search for conditions favorable for breeding in summer and for
feeding in winter has been a principal factor underlying the origin
of migration.

THEORY OF PHOTOPERIODISM

A modern view, based on studies of living behavior, favors the theory
of photoperiodism, propounded by recent investigators as the cause
of the annually induced movements of the birds. This theory holds as
its major premise that quantity of light and length of day are the
stimulating causes of migration. Its proponents urge that migration
is a phenomenon far too regular to be created anew each season merely
under stress of circumstances, such as need for food; and that it
begins before the necessity for a change in latitude becomes at all
pressing. Swallows, nighthawks (_Chordeiles minor_), shore birds,
and others may start their southward movement while the summer food
supply in the North is at peak abundance; while robins (_Turdus
migratorius_), bluebirds (_Sialia sialis_), and others may leave
an abundant food in the South in spring and press toward northern
points when the food supplies there are almost entirely lacking
and when severe cold and storms are likely to play havoc with the
advance migrants. The regularity of arrival and departure is one of
the most impressive features of migration, and since birds travel in
almost strict accordance with the calendar, the proponents of the
theory ask: What phenomenon to which we may attribute the stimulating
impulse occurs with such precise regularity as the constantly
increasing light in spring?

Experimental work has abundantly demonstrated the effect of increased
light upon the growth, flowering, and fruiting of plants. Similarly,
experiments with the common junco, or snowbird (_Junco hyemalis_),
reported by Rowan (_42, p. 121_), resulted in increased development
of the sexual organs by the end of December, although the birds
were confined in outdoor aviaries in Canada and had been exposed
to temperatures as low as -44° F. From the first of November until
early in January, the juncos were subjected to ever-increasing
light, supplied in the aviaries by electric bulbs. As regards
illumination, they were thus artificially provided with conditions
approximating those of spring. At the close of this period, it was
found that the sexual organs of the birds had attained the maximum
development normally associated with spring. With gradual reduction
of the lighting over a period of little more than 1 month, the organs
returned to their normal winter condition.

After a consideration of all evidence, including the fact that no
ultraviolet rays were used, it was concluded that the explanation
lay in the increased exercise taken during the periods of increased
light. A simple test whereby certain birds were forced by mechanical
means to take more exercise, the light being so reduced that there
was merely sufficient glow for them to see the advancing mechanism
that forced them into movement, showed that the rate of development
of the sexual organs exactly paralleled that in the birds that were
exposed to extended periods of illumination in the outdoor aviaries.
Other features in this experiment--such as the behavior of the birds
themselves--also indicated that more activity due to increased light
is the governing cause of the spring development of the sexual
organs. If this development be accepted as a controlling cause of
migration, then this experiment must be recognized as of great
importance.

Upon closer analysis, however, it is found that this theory, like
those before discussed, is open to serious objections. First, some of
our summer residents that migrate south for the winter do not stop
in equatorial regions, where they might find the periods of day and
night about equally divided, but push on beyond, some penetrating as
far south as Patagonia. Also it might be asked: If the lengthening
day is the stimulating factor, why should our summer birds wintering
in the Tropics ever start northward, as in their winter quarters
the variation in the length of day from winter to summer is
imperceptible. Like all the other theories advanced, this also, as at
present understood, is subject to unanswered criticism.




=WHEN BIRDS MIGRATE=


It is known that at any given point many species leave in fall and
return in spring. Since bird banding has had such wide application as
a method of study, it is known also that in some species one of the
parent birds (rarely both) frequently returns and nests in the same
tree, bush, or box that held its nest in the previous season (fig.
1). One ordinarily thinks of the world of birds as quiescent during
two seasons each year, at nesting time and in winter. For individual
species this is obviously the case, but when the entire avifauna of
the continent is considered it is found that there are at almost all
periods some latitudinal movements.

[Illustration: B12M

Figure 1.--The bluebird may return regularly year
after year to nest in the same hole or box that was occupied in
previous seasons.]


MOVEMENTS OF SPECIES AND GROUPS

Some species begin their fall migrations early in July, and in some
parts of the country distinct southward movements can be detected
from then until the beginning or middle of winter. For example, many
shore birds start south in the early part of July, while the goshawks
(_Astur atricapillus_), snowy owls (_Nyctea nyctea_), redpolls
(_Acanthis linaria_), Bohemian waxwings (_Bombycilia garrula_),
and many others do not leave the North until forced to do so by
the advent of severe winter weather or by lack of the customary
food. Thus, an observer in the northern part of the United States
may record an almost unbroken southward procession of birds from
midsummer to winter, and note some of the returning migrants as early
as the middle of February. Purple martins (_Progne subis_) have been
known to arrive in Florida late in January on their way north, and
the northern movement may continue among late arrivals into the first
week of June. In some species the migration is so prolonged that the
first arrivals in the southern part of the breeding range will have
performed their parental duties while others of that species are
still on their way north.

A study of these facts indicates that sometimes there exists a very
definite relationship between what we may term northern and southern
groups of individuals of the same species. A supposition, on which
additional banding work is expected later to give definite facts, is
that in the case of some species that have an extensive latitudinal
breeding range and a normal migration, the individuals that nest
farthest south migrate first in fall and proceed to the southern
part of the winter range; those that occupy the central parts of the
breeding range migrate next, and travel to regions in the winter
range north of those occupied by the first group; and finally the
individuals breeding farthest north are the last to begin their fall
migration and these remain farthest north during the winter. In
other words, this theory supposes that the southward movement of the
species is normally such that the different groups maintain their
relative latitudinal positions, both spring and fall.

[Illustration: B4503M

Figure 2.--Summer and winter homes of the black-and-white warbler. A
very slow migrant, as the birds nesting in the northern part of the
country take 50 days to cross the breeding range. The rapidity of
their advance is shown in figure 3.]

The black-and-white warbler (_Mniotilta varia_) furnishes an example.
The breeding range of this bird extends west and northwest from South
Carolina and New Brunswick as far as Great Bear Lake in northwestern
Canada (fig. 2). The bird spends the winter in southern Florida, the
West Indies, central Mexico, Central America, and northwestern South
America. In the southern part of its breeding range it is nesting in
April, but the summer residents of New Brunswick do not reach their
breeding grounds before the middle of May. Therefore, about 50 days
are required for these northbound birds to cross the breeding range,
and if 60 days be allowed for nest building, egg laying, incubation,
care of the young, and molt, they would not be ready to start
southward before the middle of July (fig. 3). Then another 50-day
trip south, and the earliest migrants from the northern areas would
reach the Gulf coast in September. But both adults and young have
been observed at Key West, Fla., by the middle of July, and on the
northern coast of South America by August 21. Since the birds at Key
West were fully 500 miles south of the breeding-range, it is evident
that they must have come from the southern part of the nesting area.

[Illustration: B4504M

Figure 3.--Isochronal migration lines of the
black-and-white warbler, showing a slow and uniform migration, the
advance across the United States being apparently only about 20 miles
a day.]

Many similar cases might be mentioned, such as the black-throated
blue warblers (_Dendroica caerulescens_), which are still observed
in the mountains of Haiti in the middle of May when others of the
species are en route through North Carolina to breeding territory in
New England or have even reached that region. Redstarts (_Setophaga
ruticilla_) and yellow warblers (_D. aestiva_), evidently the more
southern breeders in each case, are seen returning southward on the
northern coast of South America just about the time that the earliest
of those breeding in the North reach Florida on their way to winter
quarters.

[Illustartion: B2282M

Figure 4.--The Kentucky warbler, a night migrant, in
traveling to its winter quarters in Central America and northwestern
South America, uses route no. 5, figure 20.]


NOCTURNAL AND DIUNAL MIGRATION

When one recalls that most birds appear to be more or less helpless
in the dark, it seems remarkable that many should select the night
hours for extended travel. Among those that do, however, are the
great hosts of shore birds, rails, flycatchers, orioles, most of
the great family of sparrows, the warblers (fig. 4), vireos, and
thrushes, and, in fact, the majority of small birds. That it is
common to find woods and fields on one day almost barren of bird
life and on the following day filled with sparrows, warblers, and
thrushes, would indicate the arrival of migrants during the night.
The passage of flocks of ducks and geese is frequently observed by
sportsmen sitting in their blinds, but great numbers of these birds
also pass through at night, the clarion call of the Canada goose
(_Branta canadensis_) or the conversational gabbling of a flock of
ducks being common night sounds in spring and fall in many parts of
the country. The sibilant, nocturnal calls of the upland plover, or
Bartramian sandpiper (_Bartramia longicauda_), and other shore birds
during their spring and fall flights form vivid memories in the minds
of many students of migration. Observations made with telescopes
focused on the full moon have shown processions of birds. The
estimate of one observer that birds passed his point of observation
at the rate of 9,000 an hour gives some indication of the numbers of
birds that are in the air during some of the nights when migration
is at its height. While the passage of migratory birds has thus been
recorded throughout the night, the bulk of the flocks pass during the
earlier hours of the evening and toward daylight in the morning, the
periods from 8 o'clock to midnight and from 4 to 6 a. m. seeming to
be favorite times for nocturnal flight.

It has been claimed, with some reason, that small birds migrate
by night the better to avoid their enemies, and that most of the
nocturnal travelers are those that are naturally timid, sedentary,
or feeble-winged. Included in this group are not only small song and
insectivorous birds, but also such weak fliers as the rails, as well
as the wrens, the small woodland flycatchers, and other species,
which, living habitually more or less in concealment, are probably
much safer making their long flights under the protecting cloak of
darkness. This cannot fully account for the nocturnal habit, however,
since among the night migrants are the snipe, sandpipers, and
plovers, birds that are generally found in the open and are among the
more powerful fliers, some of them making flights of more than 2,000
miles across the ocean. Such exceptionally long flights, of course,
require both day and night flying.

Night travel is probably best for the majority of birds, chiefly
from the standpoint of feeding. Digestion is rapid in birds, and
yet the stomach of a bird killed during the day almost always
contains food. To supply the energy required for long flight, it is
essential that food be obtained at comparatively short intervals, the
longest of which in most species is during the hours of darkness.
If the smaller migrants were to make protracted flights by day
they would be likely to arrive at their destination at nightfall
almost exhausted, but unable to obtain food until the following
morning, since they are entirely daylight feeders. This would delay
resumption of flight and result in great exhaustion or possibly even
death were they so unfortunate as to have their evening arrival
coincident with unusually cold or stormy weather. Traveling at night,
they pause at daybreak and devote the entire period of daylight to
alternate feeding and resting. This permits complete recuperation and
resumption of the journey at nightfall.

Many species of wading and swimming birds migrate indifferently
by day or by night, as they are able to feed at all hours and are
not accustomed to seek safety in concealment. Some diving birds,
including ducks that submerge when in danger, sometimes travel over
water by day and over 1 and at night. The day migrants include,
in addition to some of the ducks and geese, the loons, cranes,
gulls, pelicans, hawks (fig. 7), swallows, nighthawks, and the
swifts (fig. 6), all strong-winged birds. The swifts, swallows,
and nighthawks (sometimes called bullbats) feed entirely on flying
insects, and use their short, weak feet and legs only for grasping
a perch during periods of rest or sleep. Thus they feed as they
travel, the circling flocks being frequently seen late in summer
working gradually southward. Years ago, before birds of prey were so
thoughtlessly slaughtered, great flocks of red-tailed hawks (_Buteo
borealis_), Swainson's hawks (_B. swainsoni_), and rough-legged
hawks (_B. lagopus_ and _B. regalis_) might be seen wheeling
majestically across the sky in the Plains States, and in the East
the flights of broad-winged hawks (_B. platypterus_), Cooper's hawks
(_Accipiter cooperi_), and sharp-shinned hawks (_A. velox_) are
still occasionally seen, although these birds do not actually travel
in flocks. To the birds of prey and possibly to the gulls also, a
day's fasting now and then is no hardship, particularly since they
frequently gorge themselves to repletion when opportunity is afforded.

The spring migrations of the blackpoll warbler (_Dendroica striata_)
and the cliff swallow (_Petrochelidon albifrons_) afford an
interesting comparison of the flights of day and night migrants.
Both spend the winter in South America, at which season they are
neighbors. But when the impulse comes to start northward toward their
respective breeding grounds, the warblers strike straight across the
Caribbean Sea to Florida, while the swallows begin their journey
by a westward flight of several hundred miles to Panama (fig. 5).
Thence they move leisurely along the western shore of the Caribbean
Sea to Mexico, and continuing to avoid a long trip over water, they
go completely around the western end of the Gulf of Mexico. This
circuitous route adds more than 2,000 miles to the journey of the
swallows that nest in Nova Scotia. The question may be asked, Why
should the swallow select a route so much longer and more roundabout
than that taken by the blackpoll warbler? The simple explanation
is that the swallow is a day migrant while the warbler travels at
night. The migration of the warbler is made up of a series of long,
nocturnal flights, alternated with days of rest and feeding in
favorable localities. The swallow, on the other hand, starts its
migration several weeks earlier and catches each day's ration of
flying insects during a few hours of aerial evolutions, which at the
same time carry it slowly in the proper direction. Flying along the
insect-teeming shores of the Gulf of Mexico, the 2,000 extra miles
that are added to the migration route are but a fraction of the
distance that these birds cover in pursuit of their food.

Although most of our smaller birds make their longest flights at
night, close observation shows that travel is continued to some
extent by day. This is particularly the case during the latter half
of a migratory season, when the birds manifest a desire to hasten to
their breeding grounds. At this time flocks of birds while feeding
maintain a movement in the general direction of the seasonal journey.
Sometimes they travel hurriedly, and while their flights may be
short, they cover considerable distances in the course of a day.




=HOW BIRDS MIGRATE=


SPEED OF FLIGHT AND SPEED OF MIGRATION

There is wide-spread misconception concerning the speed at which
birds normally fly, and even regarding the speed they can attain when
occasion demands, as when closely pursued by an enemy. It is not
unusual to hear accounts of birds flying "a mile a minute." While
undoubtedly some birds can and do attain a speed even greater than
this, such cases are exceptional, and it is safe to say that even
when pressed, few can develop an air speed of 60 miles an hour. They
do, however, have two speeds, one being the normal rate for everyday
purposes and also for migration, and an accelerated speed for escape
or pursuit; this in some cases may be nearly double the normal rate
of movement. Nevertheless, the effort required for the high speeds
could not be long sustained, certainly not for the long-distance
migratory journeys that are regularly made by most birds.

[Illustration: B4749M

Figure 5.--Migration of the cliff swallow; a day migrant that,
instead of flying across the Caribbean Sea as does the blackpoll
warbler (fig. 11), follows around the coast of Central America, where
food is readily obtained.]

The theory that migrating birds attain high speeds received
encouragement from the German ornithologist Gätke, who for many
years, made observations on birds at the island of Heligoland and
published thereon in 1891 (_21_). He postulated that the blue-throat
(_Cyanosylvia suecica_), a species of thrush smaller than the
American hermit thrush, would leave African winter quarters at dusk
and reach Heligoland at dawn, which would mean a sustained speed of
200 miles an hour; and that the American golden plover (_Pluvialis
dominion_) flew from the coast of Labrador to Brazil in 15 hours, or
at the tremendous speed of 250 miles per hour. These conclusions are
now considered unwarranted by most ornithologists.

Sportsmen also often greatly overestimate the speed at which ducks
and geese fly and sometimes attempt to substantiate their estimates
by mathematical calculations, based upon the known velocity of a
charge of shot, the estimated distance, and the estimated "lead" that
was necessary to hit the bird. If all three elements of the equation
were known with certainty, the speed of the bird could be determined
with a fair degree of accuracy. The majority of the ducks that are
reported as killed at 40, 50, or even 60 yards, however, actually
are shot at distances much less than estimated. To sight along a gun
barrel and estimate correctly the distance of a moving object against
the sky is so nearly impossible for the average gunner as to make
such calculations of little value.

During the past few years reliable data on the speed of birds have
accumulated slowly. It has been found that the common flying speed of
ducks and geese is between 40 and 50 miles an hour, and that it is
much less among smaller birds. Herons, hawks, horned larks, ravens,
and shrikes, timed with the speedometer of an automobile, have been
found to fly 22 to 28 miles an hour, while some of the flycatchers
are such slow fliers that they attain only 1 to 17 miles an hour.
Even such fast-flying birds as the mourning dove rarely exceed 35
miles an hour. All these birds can fly faster, but it is to be
remembered that at training camps during the World War, airplanes
having a maximum speed of about 80 miles an hour easily overtook
flocks of ducks that it may be supposed were making every effort
to escape. Aviators have claimed that at 65 miles an hour they can
overtake the fastest ducks, though cases are on record of ducks
passing airplanes that were making 55 miles an hour.

The greatest bird speeds that have been reliably recorded are of
the swifts (fig. 6) and the duck hawk, or peregrine falcon (_Falco
peregrinus_) (fig. 7). An observer in an airplane in Mesopotamia
reported that swifts easily circled his ship when it was traveling at
68 miles an hour. To do this, the birds certainly were flying at a
speed as high as 100 miles an hour. Once a hunting duck hawk, timed
with a stop watch, was calculated to have attained a speed between
165 and 180 miles an hour.

The speed of migration, however, is quite different from that
attained in forced flights for short distances. A sustained flight of
10 hours a day would carry herons, hawks, crows, and smaller birds
from 100 to 250 miles, while ducks and geese might travel as much as
400 to 500 miles in the same period. Measured as air-line distances,
these journeys are impressive and indicate that birds could cover the
ordinary migration route from the northern United States or even from
northern Canada to winter quarters in the West Indies or in Central
America or South America in a relatively short time. It is probable
that individual birds do make flights of the length indicated and
that barn swallows (_Hirundo erythrogaster_) seen in May on Beata
Island, off the southern coast of the Dominican Republic, may have
reached that point after a nonstop flight of 350 miles across the
Caribbean Sea from the coast of Venezuela. Nevertheless, whether they
continue such journeys day after day is doubtful.

[Illustration: B988M

Figure 6.--Chimney swift: a speedy day migrant, the flight, of which
on occasions probably exceeds 100 miles an hour.]

It seems more likely that migrations are performed in a leisurely
manner, and that after a flight of a few hours the birds pause to
feed and rest for 1 or several days, particularly if they find
themselves in congenial surroundings. Some indication of this is
found in the records of banded birds. Considering only the shortest
intervals that have elapsed between banding in the North and recovery
in southern regions, it is found that usually a month or more is
taken to cover an air-line distance of a thousand miles. For example,
a black duck (_Anas rubripes_) banded at Lake Scugog, Ontario, was
killed 12 days later at Vicksburg, Miss. If the bird was taken
shortly after its arrival, the record would indicate an average
daily flight of only 83 miles, a distance that could have been
covered in about 2 hours' flying time. Among the thousands of banding
records obtained in recent years, evidences of such rapid flight are
decidedly scarce, for with few exceptions all thousand-mile flights
have required 2 to 4 weeks or more. The greatest speed thus far
recorded for a banded bird is that of a mallard (_A. platyrhynchos_)
banded on November 23, 1930, in Green Bay, Wis., and shot 5 days
later, 900 miles away, near Georgetown, S. C. This bird doubtless
flew at least 1,000 miles in the 5 days, as its route probably was
not in a direct air-line, but, even so, the average daily distance
was only 200 miles, which could easily have been covered in 5 hours.

It seems certain that migratory journeys are performed at the normal
rate of flight, as this would best conserve the strength of the birds
and eliminate the fatigue that would result from effort required for
great speed. Migrating birds passing lightships and lighthouses,
or crossing the face of the moon, have been observed to fly without
hurry or evidence of straining to attain high speed.

[Illustration: B213M

Figure 7.--Duck hawk, or peregrine falcon (Falco peregrinus): a day
migrant and one of the fastest and most graceful fliers of all North
American birds.]

The speed of migration also is demonstrated by the dates of arrival,
particularly during the spring movement. The Canada goose affords
a typical example of regular, but slow, migration. Its advance
northward at this season is at the same rate as the advance of the
season (fig. 8). In fact, the isotherm of 35° F. appears to be a
governing factor in the speed at which these geese move north, and
over their entire trip the vanguard follows closely the advance of
this isotherm.

Few species perform such regular migrations, many waiting in their
winter homes until spring is well advanced and then moving rapidly
to their breeding-grounds. Sometimes this advance is so rapid that
the later migrants actually catch up with species that for a month or
more may have been pressing slowly but steadily northward.

One of the best examples of rapid migration is found in the
gray-cheeked thrush (_Hylocichla minima aliciae_). This bird winters
in Colombia, Ecuador, Peru, Venezuela, and British Guiana and does
not start its northward journey until many other species are well on
their way. It does not appear in the United States until the last of
April--April 25, near the mouth of the Mississippi, and April 30 in
northern Florida (fig. 9). A month later, or by the last week in May,
the bird is seen in northwestern Alaska, the 4,000-mile trip from
Louisiana having been made at an average speed of about 130 miles a
day.

Another example of rapid migration is furnished by the yellow, or
summer, warbler. Coming from the Tropics, the birds reach New
Orleans about April 5, when the average temperature is 65° F.
Traveling north much faster than does the season, they reach their
breeding grounds in Manitoba the latter part of May, when the average
temperature is only 47°. Encountering progressively colder weather
over their entire route, they cross a strip of country in the 15 days
from May 11 to 25 that spring takes 35 days to cross. This "catching
up" with spring is habitual in species that winter south of the
United States and in most of the northern species that winter in the
Gulf States. To this rule there appear to be only six exceptions--the
Canada goose, the mallard, the pintail (_Dafila acuta_), the crow
(_Corvus brachyrhynchos_), the red-winged blackbird (_Agelaius
phoeniceus_), and the robin.

[Illustration: B4508M

Figure 8.--Migration of the Canada goose. The northward movement
keeps pace with the advance of spring, in this case the advance of
the isotherm of 35° F. agreeing with that of the birds.]

The blue goose (_Chen caerulescens_) (fig. 10) presents a striking
example of a late but very rapid spring migration. Practically
all members of the species winter in the great coastal marshes of
Louisiana, where 50,000 or more may be seen grazing in the "pastures"
or flying overhead in flocks of various sizes. Their breeding
grounds are chiefly on Baffin Island and on Southampton Island in
the northern part of Hudson Bay, in a region where conditions of
severe cold prevail except for a few weeks each year. The birds seem
to realize that even though the season in their winter quarters is
advancing rapidly, their nesting grounds are still covered with a
heavy blanket of ice and snow. Accordingly they remain in the coastal
marshes until the last of March or the first of April, when the local
birds are already busily engaged with the duties of reproduction.
The flight northward is rapid, almost nonstop, so far as the United
States is concerned, for although the birds are sometimes recorded
in large numbers in the Mississippi Valley, including eastern South
Dakota, and in southeastern Manitoba, there are few records anywhere
along the route of such great flocks as are known to winter in
Louisiana. When the birds arrive in the James Bay region of Canada
they apparently enjoy a prolonged period of rest, as they are not
noted in the vicinity of their breeding grounds until the first of
June. During the first 2 weeks of that month they pour into the
tundra country by the thousands, and each pair immediately sets about
the business of rearing a brood.

[Illustration: B4505M

Figure 9.--Isochronal migration lines of the gray-cheeked thrush; an
example of rapid migration. The distance from Louisiana to Alaska is
about 4,000 miles and is covered at an average speed of about 130
miles per day. The last part of the journey is covered at a speed
that is several times what it is in the Mississippi Valley.]

The robin has been mentioned as a slow migrant, and as a species it
takes 78 days to make the 3,000-mile trip from Iowa to Alaska, a
stretch of country that is crossed by advancing spring in 68 days.
In this case, however, it does not mean that individual robins are
necessarily slow, for probably the northward movement of the species
depends upon the continual advance of birds from the rear, the first
individuals arriving in a suitable locality remaining to nest, while
the responsibility of the northward movement of the species is
continued by those still to come.

[Illustration: B4766M

Figure 10.--Blue goose, a late but rapid spring migrant that winters
on the coast of Louisiana and breeds on Baffin and Southampton
Islands and flies between summer and winter areas practically without
stops. Photograph by Paul W. Hoffman.]

Special interest attaches to the great variation in the speed
at which birds travel in different sections of the broad flyway
extending from the Gulf of Mexico to the Arctic Ocean by way of the
Mississippi and Mackenzie Valleys. The blackpoll warbler furnishes an
excellent example (fig. 11). This species winters in north-central
South America and migrates in April across the West Indies to
Florida. From this point some individuals fly northwest to the
Mississippi Valley, north to Manitoba, northwest to the Mackenzie
River, and thence almost due west to western Alaska. In tracing
the long route of these birds it is found that a fairly uniform
average speed of 30 to 35 miles a day is maintained from the Gulf
to Minnesota. Then comes a spurt, for a week later the blackpolls
have reached the central part of the Mackenzie Valley, and by the
following week they are observed in northwestern Alaska. During
the latter part of the journey, therefore, many individuals must
average more than 200 miles a day. They use 30 days in traveling from
Florida to southern Minnesota, a distance of about 1,000 miles, and
scarcely half that time to cover the remaining 2,500 miles to Alaska.
It should be noted that the increased speed is directly associated
with the change in direction, the north-and-south course in the
Mississippi Valley being accomplished slowly, while the northwesterly
course across Canada is made at a much greater speed. Increased
speed across western Canada to Alaska is also shown by many other
species. A study of all species traveling up the Mississippi Valley
indicates an average speed of about 23 miles a day. From southern
Minnesota to southern Manitoba 16 species maintain an average speed
of about 40 miles a day. From that point to Lake Athabaska, 12
species travel at an average speed of 72 miles a day; while 5 others
travel to Great Slave Lake at 116 miles a day; and another 5 species
cover 150 miles a day to reach Alaska. This change is in correlation
with a corresponding variation in the isothermal lines, which turn
northwestward west of the Great Lakes.

[Illustration: B4495M

Figure 11.--Migration of the blackpoll warbler. The solid isochronal
lines show the places at which these birds arrive at the same time.
As the birds move northward these lines become farther apart, showing
that the warblers move faster with the advance of spring. From April
30 to May 10 the average speed is about 30 miles a day, while from
May 25 to May 30 it is increased to more than 200 miles.]

As has been previously indicated, the advance of spring in the
northern interior is much more rapid than in the Mississippi Valley
and on the Gulf coast. In other words, in the North, spring comes
with a rush, and during the height of the migration season in
Saskatchewan the temperature in the southern part of the Mackenzie
Valley just about equals that in the Lake Superior area, which is
700 miles farther south. Such conditions, coupled with the diagonal
course of the birds across this region of fast-moving spring, exert
a great influence on migration and are the chief factors in the
acceleration of speed of travel.

Variations in speed of migration in different parts of the country
are illustrated also by the movements of the cliff swallow (fig.
5), which breeds from Mexico to Alaska and winters in Brazil and
Argentina. It would be expected in spring to appear in the United
States first in Florida and Texas, then in the southern Rocky
Mountain region, and finally on the Pacific coast. As a matter of
fact, however, the earliest spring records come from north-central
California, where the bird usually is common before the first
arrivals are observed in Texas or Florida. The route taken, for many
years a migration problem, was solved when it was found that these
swallows went around the Gulf of Mexico rather than across it. The
isochronal lines on the map show the more rapid advance along the
Pacific coast. By March 20, when the vanguard has not quite reached
the lower Rio Grande in Texas, the species is already north of San
Francisco in California.


ALTITUDES AT WHICH BIRDS TRAVEL

At one time students of bird migration held firmly to the theory
that normal migration takes place at heights above 15,000 feet,
reasoning (somewhat uncertainly) that flying becomes easier as
altitude is gained. Since the development of the airplane, however,
and with it man's exploration of the upper regions of the air, it
has become common knowledge that rarefied atmosphere adds greatly to
the difficulties of flight. This is due not only to the reduction
in oxygen (whether for gasoline engine or the lungs of a bird) but
also to the lack of buoyancy of rarefied air. Such birds as vultures,
pelicans, cranes, and some of the hawks feel this the least, since
compared with body weight the supporting surface of their wings is
very great, but for the smaller and shorter winged birds lack of
buoyancy at high altitudes presents a difficult obstacle in flight.
Even when flying close to the earth, small birds have to keep their
wings in rapid motion.

Another postulate favoring the high-altitude flying theory was
that the wonderful vision of birds was their sole guidance during
migratory flights; and to keep landmarks in view the birds were
obliged to fly high, particularly when crossing wide areas of water.
This will be considered in greater detail under Orientation (p. 23),
so here it will be sufficient to say that birds rely only in part
upon vision to guide them on migration. Also, it is to be remembered
that there are definite physical limitations to the range of
visibility even under perfect atmospheric conditions. Chief of these
is the curvature of the earth's surface. Thus, if birds flew over the
Gulf of Mexico to Louisiana and Florida at a height of 5 miles, they
would still be unable to see a third of the way across. And yet this
trip is made twice each year by thousands of thrushes, warblers, and
others.

Actual knowledge of the altitude of migratory flight is scanty,
though estimates obtained by means of the telescope, and still more
accurate data resulting from altimeter observation from airplanes,
are slowly accumulating. It is, of course, obvious that some birds
that cross mountain ranges during migration must attain a great
altitude. Observers at an altitude of 14,000 feet in the Himalayas
have recorded storks and cranes flying so high that they could be
seen only through field glasses. Being beyond the range of unaided
vision they must have been at least 6,000 feet above the observers,
or at an actual altitude of 20,000 feet above sea level. Such cases,
however, are exceptional, as aviators have reported that they rarely
meet birds above an altitude of 5,000 feet.

It is now known that migration in general is performed below an
altitude of 3,000 feet. Some proof of this statement is available.
Observations made from lighthouses and other points of vantage
indicate that migrants commonly travel at altitudes of a very few
feet to a few hundred feet above sea or land. Sandpipers, sanderlings
(_Crocethia alba_), and northern phalaropes (_Lobipes lobatus_),
observed in migration on the Pacific oceanic route, have been noted
to fly so low that they were visible only as they topped a wave.
Observers stationed at lighthouses and lightships off the English
coast have similarly recorded the passage of land birds, which
sometimes flew just above the surface of the water, and rarely above
200 feet. During the World War broad areas in the air were under
constant close surveillance, and among the airplane pilots and
observers many took more than a casual interest in birds. Of the
several hundred records resulting from their observations only 36
were of birds flying above 5,000 feet, and only 7 above 8,500 feet.
Cranes were once recorded at an altitude of 15,000 feet, while the
lapwing (_Vanellus vanellus_) was the bird most frequently seen at
high levels, 8,500 feet being its greatest recorded altitude.

These observations naturally relate only to daytime travelers, but
there is no reason to believe that nocturnal migration is performed
at higher altitudes. The fact that many birds are killed each year by
striking the lanterns at lighthouses, or other man-made obstructions,
does not, however, furnish conclusive proof that low altitudes are
generally used during nocturnal flight, for it should be recalled
that these accidents occur chiefly in foggy or unsettled weather, and
also, that powerful lights have a great attraction for many species
of birds. The altitude at which birds travel is affected by other
weather conditions also. For example, flight at the higher elevations
is facilitated on clear, warm days by the currents of warm air that
ascend from broad areas.


ORIENTATION

There probably is no single aspect of the entire subject of bird
migration that challenges our admiration for birds so much as the
unerring certainty with which they cover thousands of miles of land
and water to come to rest in exactly the same spot where they spent
the previous summer or winter. The records of birds marked with
numbered bands afford abundant proof that the same individuals of
many species will return again and again to their identical nesting
sites. These data show also that many individuals migrate in fall
over the same route, year after year, making the same stops, and
finally arriving at the precise thicket that served them in previous
winters.

The faculty that enables these birds to point their course accurately
over vast expanses of land and water may for want of a better term
be called a "sense of direction." Man recognizes this sense in
himself, though usually it is imperfect and frequently at fault.
Nevertheless the facility with which experienced hunters and woodsmen
locate tiny camps or other points in forested or mountainous country,
frequently cloaked by darkness or fog, with all recognizable
landmarks obliterated seems due to this faculty. Ability to travel
with precision over unmarked trails is not limited either to birds
or to man. It is likewise possessed by many mammals as well as by
some insects and fishes, the well-known migrations of the salmon
(_Oncorhynchus_) and the eel (_Anguilla_) being notable examples.

Ability to follow a more or less definite course to a definite goal
is evidently part of an inherited faculty. Both the path and the goal
must have been determined either when the habit originated or in the
course of its subsequent evolution. The theory is sometimes advanced
that the older and more experienced birds lead the way, showing the
route to their younger companions. This explanation may be acceptable
for some species, but not for those in which adults and the young
migrate at different times. The young cowbird that is reared by
foster parents flocks with others of its kind when grown and in many
cases can hardly be said to have adult guidance in migration. An
inherited migratory instinct with a definite sense of the goal to
be reached and the route to be followed must be attributed to these
birds.

It is known, however, that birds possess wonderful vision. If they
also have retentive memories, subsequent trips over the route may
well be steered in part by recognizable landmarks. The arguments
against the theory of vision and memory are chiefly that much
migration takes place at night and that great stretches of the open
sea are crossed without hesitation. Nevertheless, the nights are
rarely so dark that all terrestrial objects are totally obscured,
and such features as coast lines and rivers are just those that are
most likely to be seen in the faintest light, particularly by the
acute vision of a bird and from its aerial points of observation. But
some birds fly unerringly through the densest fog. Members of the
Biological Survey, proceeding by steamer from the island of Unalaska
to Bogoslof Island in Bering Sea through a fog that was so heavy as
to make invisible every object beyond a hundred yards, recorded the
fact that flocks of murres, returning to Bogoslof, after quests for
food, broke through the wall of fog astern, flew by the vessel, and
disappeared into the mists ahead. The ship was heading direct for the
island by the use of compass and chart, but its course was no more
sure than that of the birds.

Some investigators have asserted that the sense of direction has its
seat in the ears or nasal passages and thus that the bird is enabled
to identify air currents and other phenomena. It has been found that
disturbance of the columella, or the semicircular canals of the
inner ear, will destroy the homing instinct of the racing pigeon,
but experiments in the form of delicate operations, or closing the
ears with wax, prove such a serious shock to the sensitive nervous
system of the bird that they cannot be considered as affording
conclusive evidence. Several years ago careful studies were made of
the homing instinct of the sooty and noddy terns (_Sterna fuscata_
and _Anoüs stolidus_), tropical species that in the Atlantic region
reach their most northern breeding point on the Dry Tortugas Islands,
off the southwest coast of Florida. They are not known to wander
regularly any appreciable distance farther north. It was found that
some were able to return to their nests on the Tortugas after they
had been taken on board ship, confined in cages below deck, and
carried northward distances varying from 400 to 800 miles before
being released. Landmarks of all lands were entirely lacking, and the
birds certainly were liberated in a region in which they had had no
previous experience.

Possibly the "homing instinct" as shown by these terns, by the
man-of-war birds (_Fregata minor_), that are trained and used as
message carriers in the Tuamotu, Gilbert, and Marshall Islands, and
by the homing pigeon, is not identical with the sense of perceptive
orientation that figures in the flights of migratory birds.
Nevertheless, it seems closely akin and is probably caused by the
same impulses, whatever they may be and however they may be received.
It is to be remembered, however, that while homing may involve flight
from a point that the bird has never before visited, the flight is
always to a known point — that is, the bird's nest— while, on the
other hand, the first migratory flight is always from the region
of the bird's birth to a region it has never before visited. The
spring migration might, of course, be more nearly considered as true
"homing."

At the present time some students lean strongly toward the possible
existence of a "magnetic sense" as being the important factor in the
power of geographical orientation. No direct evidence in support
of this has been obtained, but it is not impossible that there may
exist some form of physiological sensibility to the phenomena of
terrestrial magnetism. The theory as laid down (chiefly by European
investigators) is highly complex, but briefly stated it is based on
a supposed sensitiveness of birds to the magnetic influences that
cause variations in the declination and dip of magnetic needles. Some
experimental work already done lends a little support to the theory
but it is still far from established.

In concluding this discussion of orientation it is pertinent to
point out that the migratory instinct appears to be more or less
transitory, that it is not persistent over an extended period.
Migratory birds may be arrested en route, either by natural
conditions, such as unusual food supplies, or forcibly by the act of
man, and detained until the end or nearly the end of the migratory
season, and then may not attempt to finish the journey, apparently
having lost the migratory impulse. In the fall and early winter of
1929, abundant food and an open season caused an unusual number of
mallard ducks to arrest their migration and remain in western Montana
and northern Idaho. Later, however, a heavy snowfall with subzero
temperatures suddenly cut off the food supply, with the result that
great numbers of the birds starved to death, when a flight of a few
hours would have carried them to a region of open water and abundant
food.


SEGREGATION DURING MIGRATION

During the height of the northward movement in spring the woods
and thickets may be suddenly filled with several species of wood
warblers, thrushes, sparrows, flycatchers, and others, which
it is natural to conclude have traveled together and arrived
simultaneously. Probably they did, but such combined migration is by
no means the rule for all species.

As a group the wood warblers (Compsothlypidae) probably travel more
in mixed companies than do any other single family of North American
birds. The flocks are likely to be made up of several species, spring
and fall, with both adults and young. Sometimes swallows, sparrows,
blackbirds, and some of the shore birds also migrate in mixed flocks.
In fall, great flocks of blackbirds frequently sweep south across
the Plains States, and occasionally one flock will contain bronzed
grackles (_Quiscalus quiscula_), red-winged blackbirds, yellow-headed
blackbirds (_Xanthocephalus xanthocephalus_), and Brewer's blackbirds
(_Euphagus cyanocephalus_).

On the other hand, many species keep strictly to themselves. It would
be difficult for any other kind of bird to keep in company with a
bird of such rapid movements as the chimney swift, which is rarely
found associated with any other species at any season. Nighthawks,
or bullbats, also fly in separate companies, as usually do crows,
waxwings, crossbills, bobolinks, and kingbirds. Occasionally, a flock
of ducks will be observed to contain several species, but generally
when they are actually on migration the individuals of each species
separate and travel with others of their own kind. The flocks of
blue geese, previously mentioned in connection with speed of flight
(p. 18), frequently have with them a few of the closely related snow
geese (_Chen hyperborea_), particularly in the eastern part of their
winter range. The proportion here is usually about 10 to 1, but
farther west the numbers of snow geese increase until they outnumber
their blue relatives.

The adults of most perching birds drive the young away when they are
grown, probably to be relieved of the necessity of providing for
them, and also in order that the parents may have opportunity to rest
and renew their plumage before starting for winter quarters. The
young birds are therefore likely to drift together and, having no
further responsibility, may start south ahead of their parents. In
contrast with this indifference on the part of the adults of perching
birds, Canada geese and some others, remain in family groups, the
parent birds undergoing the wing molt that renders them flightless
during the period of growth of their young, so that old and young
acquire their full plumage at the same time and thus are able to
start south together. The large flocks, therefore, are composed
of many families that band together, and when they separate into
V-shaped units it is probably correct to assume that it is an old
bird that leads the group. Where there is segregation of the sexes,
the young birds usually accompany their mothers, as is the case with
some of the ducks. After the females start to incubate their eggs,
the males of most species of ducks flock by themselves and remain
together until fall.

The males and females of some species may migrate either
simultaneously or separately. In the latter case it is usually the
males that arrive first, sometimes great flocks of male birds, as in
the red-winged blackbird, reaching a locality several days before any
of the females. This is particularly the rule in spring; the first
robins are usually found to be males, as also are the first song
sparrows (_Melospiza melodia_), rose-breasted grosbeaks (_Hedymeles
ludovicianus_), and scarlet tanagers (Piranga erythromelas). This
early arrival of the males has been explained on the theory of
territorial possession, under which the male selects the area where
it elects to breed, each individual attempting to protect a definite
territory from trespass by other males of his own kind, at the same
time singing or otherwise announcing his presence and inviting the
later arriving females to examine the territory that he has selected
for nesting. The long-billed marsh wren (_Telmatodytes palustris_)
is a noteworthy example, and the males of this species may
enthusiastically build several dummy nests before the females arrive.

In a few species, the males and females apparently arrive at the
breeding grounds together and proceed at once to nest building. In
fact among the shore birds, ducks, and geese, courtship and mating
may take place, in whole or in part, while the birds are in the South
or on their way north, so that when they arrive at the northern
nesting grounds they are paired and ready to proceed at once with the
raising of their families. Mallards and black ducks may be observed
in pairs as early as January, the female leading and the male
following when they take flight. Naturally these mated pairs migrate
north in company, and it was largely to protect such species that
duck shooting in spring was abolished by Federal law several, years
ago.

Many shore birds nest well within the Arctic Circle, and it is the
opinion of ornithologists that most of these birds share, at least
in part, the habits of the phalaropes, a family in which the male
assumes the entire care of the eggs and young. If this be true, it
explains why in southern latitudes so many of the earliest fall
arrivals are females that may have deserted the breeding grounds
after the eggs were laid.

Migratory flights are frequently accomplished in close flock
formation, as with the shore birds, blackbirds, and waxwings, and
especially some of the sparrows--the snow buntings (_Plectrophenax
nivalis_), longspurs, juncos, and tree sparrows (_Spizella arborea_).
Other species, however, though they travel in flocks, maintain a very
loose formation; examples are the turkey vultures (_Cathartes aura_),
the hawks, swifts, blue jays, swallows, warblers, and bluebirds.
Still others, the grebes, great horned owls (_Bubo virginianus_),
winter wrens (_Nannus hiemalis_), shrikes, and belted kingfishers
(_Megaceryle alcyon_), for example, ordinarily travel alone, and when
several are found in close proximity it is an indication that they
have been drawn together by unusual conditions, such as abundant food.




=WHERE BIRDS MIGRATE=


DISTANCES OF MIGRATION VARY

Definite evidence shows that both the length and the duration of
the migratory journey vary greatly. The bobwhite and the western
quails, the cardinal (_Richmondena cardinalis_), the Carolina wren
(_Thryothorus ludovicianus_), and probably some of the titmice and
woodpeckers, which are apparently nonmigratory, may round out their
full period of existence without at any time going more than 10 miles
from the nest where they were hatched.


SHORT AND UNDETERMINED MIGRATIONS

Song sparrows, meadow larks (_Sturnella_), blue jays (_Cyanocitta
cristata_), and some other species make such short migrations that
the movement is difficult to detect, as individuals may be found in
one area throughout the year. Thus, at the southern part of the range
there is merely a concentration in winter, the summer individuals
being entirely sedentary. Speculation is useless on the distances
of individual migration without definite evidence concerning the
precise winter quarters of birds that summer in a particular part of
the breeding range of the species, but from the records of banded
birds important evidence is becoming available. Eventually it may be
possible to say definitely just how far the song sparrows that nest
in northern New England and the Maritime Provinces of Canada travel
to their winter quarters, and whether the blue jays of New York and
the upper Mississippi Valley remain throughout the winter in their
breeding areas, or move farther south and relinquish their places to
individuals from southern Canada.

An illustration of what is now known on this subject is found in the
case of the robin. This bird occurs in the Middle Atlantic States
throughout the year, in Canada only in summer, and along the Gulf
coast only as a winter resident. On the Atlantic coast its movements
are readily ascertained, since, for example, in the section about
Washington, D. C., the breeding robin is the southern variety
(_Turdus migratorius achrusterus_), which is found there from the
first of April to the last of October, when its place is taken (in
smaller numbers) by the northern robin (_T. m. migratorius_), which
arrives about the middle of October and remains until the following
April. It is probable that a similar interchange of individual robins
occurs throughout a large part of the rest of its range, the hardy
birds from the north being the winter tenants in the abandoned summer
homes of the southern birds.

The red-winged blackbirds that nest in northern Texas are almost
sedentary, but in winter they are joined by representatives of other
subspecies that nest as far north as the Mackenzie Valley.


VARIABLE MIGRATIONS WITHIN SPECIES

The difference in characters between subspecies has been used by
students of migration to discover other interesting facts concerning
variations of the migratory flight between closely related birds
that breed in different latitudes. The familiar eastern fox sparrow
(_Passerella iliaca iliaca_), for example, breeds from northwestern
Alaska to Labrador, and in winter is found concentrated in the
southeastern part of the United States. It thus travels a long
distance each year. On the west coast of the continent, however, six
subspecies of this bird breed in rather sharply delimited ranges,
extending from the region of Puget Sound and Vancouver Island to
Unimak Island, at the end of the Alaska Peninsula. One of these,
known as the sooty fox sparrow (_P. i. fuliginosa_), breeds in the
Puget Sound area and makes practically no migration at all, while the
other races, nesting on the coast of British Columbia and Alaska,
are found in winter chiefly in California. The races that breed
farthest north are in winter found farthest south, illustrating a
tendency for those birds that are forced to migrate to pass over
those so favorably located that they have no need to leave their
breeding areas, while the northern birds settle for the winter in the
unoccupied areas farther south (fig. 12).

Another example of the same kind is found in the case of the Maryland
yellowthroat (_Geothlypis trichas_) of the Atlantic coast. Birds
occupying the most southern part of the general range are almost
nonmigratory, residing throughout the year in Florida, while those
breeding as far north as Newfoundland go to the West Indies for
the winter, thus passing directly over the home of their southern
relatives.

[Illustration: B4774AM

Figure 12.--Migration of Pacific-coast forms of the fox sparrow.
The breeding ranges of the different races are encircled by solid
lines, while the winter ranges are dotted. The numbers indicate the
areas used by the different subspecies, as follows: 1, Shumagin fox
sparrow; 2, Kodiak fox sparrow; 3, Valdez fox sparrow; 4, Yakutat
fox sparrow; 5, Townsend fox sparrow; 6, sooty fox sparrow. (After
Swarth; courtesy of the Museum of Vertebrate Zoology, University of
California.)]

The palm warbler (_Dendroica, palmarum_), which breeds from Nova
Scotia and Maine west and northwest to southern Mackenzie, has been
separated into two subspecies. Those breeding in the interior of
Canada (_D. p. palmarum_) make a 3,000-mile journey from Great Slave
Lake to Cuba, passing through the Gulf States early in October. After
the bulk have passed, the palm warblers from the Northeastern States
and Provinces (_D. p. hypochrysea_) drift slowly into the Gulf coast
region, where they remain for the winter. Their migratory journey is
about half as long as that of the northwestern subspecies.

There is no invariable law governing the distance of migration,
although in general it is found that where a species has an extensive
range, the subspecies that breed farthest north go farthest south to
spend the winter


FALL FLIGHTS NOT FAR SOUTH OF BREEDING RANGES

Some other species that have extensive summer ranges, for instance,
the pine warbler (_Dendroica pinus_), rock wren (_Salpinctes
obsoletus_), field sparrow (Spizella pusilla), loggerhead shrike
(_Lanius ludovicianus_), and black-headed grosbeak (Hedymeles
melanocephalus), are found to concentrate during the winter season
in the southern part of the breeding range, or to occupy additional
territory that is only a short distance farther south. The entire
species may thus be confined within a restricted area for the period
of winter, and then, with the return of warmer weather, spreads out
to reoccupy the full range.

There are many species, including the tree sparrow, slate-colored
junco, and Lapland longspur (_Calcarius lapponicus_), that nest in
Canada and winter in the United States; while others, including the
vesper sparrow (_Pooecetes gramineus_), chipping sparrow (_Spizella
passerina_), grackles, red-winged blackbird, bluebird, the woodcock
(_Philohela minor_), and several species of ducks, nest in the
northern United States and move south for the winter to areas along
the Gulf of Mexico. This list includes the more hardy species, some
individuals of which may linger in protected places well within the
reach of severe cold, as, for example, Wilson's snipe, or jacksnipe
(_Capella delicata_), which frequently is found during subzero
weather in parts of the Rocky Mountain region where warm springs
assure a food supply. More than 100 of our summer birds leave the
United States entirely and spend the winter id the West Indies or in
Central America or South America. For example, the Cape May warbler
(_Dendroica tigrina_), which breeds from northern New England,
northern Michigan, and northern Minnesota, north to New Brunswick,
Nova Scotia, and nearly to Great Slave Lake, is concentrated in
winter chiefly in the West Indies, its metropolis at this season
being the island of Hispaniola.

[Illustration: B3763M

Figure 13.--Barn Swallow, a bird that has so long a migration route
that some individuals breed north to Yukon and Alaska, while the
winter range extends south to Argentina, 7,000 miles away.]


LONG-DISTANCE MIGRATIONS

Some of the common summer residents are not content with a trip to
northern South America, but push on across the Equator and finally
come to rest for the winter in the pampas of Argentina, or even in
Patagonia. Thus some species that are more or less associated with,
each other in summer, as nighthawks, barn swallows, cliff swallows,
and some of the thrushes may also occupy the same general winter
quarters in Brazil. Some individual nighthawks and barn swallows
(fig. 13) travel still farther, and of all North American land birds
these species probably have the longest migration route, as they
occur north to Yukon and Alaska, and south to Argentina, 7,000 miles
away. Such seasonal flights are exceeded in length, however, by the
journeys of several species of water birds, chiefly members of the
suborder of shore birds. In this group are 19 species that breed
north of the Arctic Circle and winter in South America, 6 of them
going as far south as Patagonia, and thus having a migration route
more than 8,000 miles in length.

[Illustration: B1035M

Figure 14.--Arctic tern. The longest flight known for an individual
bird was accomplished by an arctic tern that in 3 months flew from
the coast of Labrador to the coast of southeastern Africa.]

The arctic tern (_Sterna paradisaea_) is the champion "globe trotter"
and long-distance flier (figs. 14 and 15). Its name "arctic" is well
earned, as its breeding range is circumpolar and it nests as far
north as it can find a suitable place. The first nest to be found
in this region was only 7½° from the North Pole, and it contained
a downy chick surrounded by a wall of newly-fallen snow that had
been scooped out by the parent. In North America it breeds south
in the interior to Great Slave Lake, and on the Atlantic coast to
Massachusetts. After the young are grown, the arctic terns disappear
from their North American breeding grounds, and a few months later
they may be found in the Antarctic region, 11,000 miles away. Until
very recently the route followed by these hardy fliers was a complete
mystery, for although a few scattered individuals have been noted
south as far as Long Island, the species is otherwise practically
unknown along the Atantic coasts of North America and South America.
It is, however, known as a migrant on the west coast of Europe and
Africa. By means of numbered bands the picture is now developing of
what is apparently not only the longest but also one of the most
remarkable of all migratory journeys.

Judging by the evidence at present available, it seems likely that
the arctic terns of eastern North America originally found their way
here from the Old World, probably by way of Iceland and Greenland.
Consequently when the time comes for them to migrate to winter
quarters they do not go directly south as do the common (_Sterna
hirundo_) and Forster's terns (_S. forsteri_), but instead, they fly
back eastward along their ancestral route across the Atlantic to
the shores of Europe and then go south along the African coast to
their winter home; those that breed in the northwestern part of the
continent, as in Alaska, probably migrate chiefly down the western
coast, as the species is not infrequently reported on the coast of
California and also on the western coast of South America.

[Illustration: B4750M

Figure 15.— Distribution and the migration of the arctic terns of
eastern North America. The route indicated for this bird is unique,
as no other species is known to breed abundantly in North America and
to cross the Atlantic Ocean to and from the Old World. The extreme
summer and winter homes are 11,000 miles apart, and as the route
taken is circuitous, these terns probably fly at least 25,000 miles
each year.]

The evidence yielded by banding consists of only three definite
cases, but their interpretation seems to permit but one conclusion:
All three birds were banded as downy chicks, one on July 3, 1913, at
Eastern Egg Rock, Maine,[3] and the other two at the Red Islands,
Turnevik Bay, Labrador, on July 22, 1927, and July 23, 1928. The
first was found dead in the Niger River delta, West Africa, in August
1917, while the Labrador birds were recovered near La Rochelle,
France, on October 1, 1927, and at Margate, near Port Shepstone,
Natal, South Africa, on November 14, 1928. The flight shown by this
last record is the longest known, the trip, between 8,000 and 9,000
miles, being accomplished in less than 3 months.

[Footnote 3: Recorded at the time of banding as a common tern, a
natural error, as the downy young of common and arctic terns look
almost exactly alike.]

Probably no other animal in the world enjoys as many hours of
daylight as does the arctic tern, since for these birds the sun never
sets during their nesting season in the northern part of the range,
while during their sojourn in the south, daylight is continuous.
During several months of the year they have 24 hours of daylight and
during the other months considerably more daylight than darkness.




=ROUTES OF MIGRATION=


While it is beyond question that certain general directions of flight
are constantly followed by migratory birds, it is well to remember
that the term "migration route" is to some extent a theoretical
concept, concerned entirely with the lines of general advance or
retreat of a species, rather than the exact course followed by
individual birds. Even the records of banded birds usually show
no more than the places of banding and recovery, and one must
have recourse to intermediate records and to reasoning based on
probabilities to fill in details of the flyway actually traversed
between the two points.

There is also infinite variety in the routes covered during migration
by different species. In fact, the choice of migration highways is
so wide that it seems as if the routes of no two species coincide.
Differences in distance traveled, in time of starting, in speed of
flight, in geographical position, in latitudes of breeding and of
wintering grounds, and in other factors, all contribute to this
great variation of migration routes. Nevertheless, there are certain
factors that serve to guide the avian travelers along more or less
definite lines, and it is possible to define general lines of
migration for the majority of species.

It has frequently been observed that migrating birds have a tendency
to follow major topographic lines on the earth's surface when their
trend is in the general direction of the birds' journey. Bird
migration is generally thought of as a north-and-south movement,
with the lanes of heavier concentration following the coasts,
mountain ranges, and principal river valleys. To a considerable
extent this is the case, particularly in North America, where the
coast lines, mountain chains, and the larger rivers in general run
north and south. Students of American birds thus have exceptionally
good opportunities to study migratory movements. In cases where the
migration is a long one, however, the notion must be abandoned that
the birds' flight is restricted to particular narrow routes that
follow river valleys and the like, as many species seem to disregard
utterly such apparently good natural flyways as river valleys. For
example, the Arkansas River has a general east and west course for a
great part of its length, and while it does constitute a highway for
many perching birds en route from the Mississippi Valley to the Rocky
Mountain region, some of the hawks and many ducks and shore birds pay
the valley scant attention. They may arrest their fall journey to
feed among cottonwoods or along sand bars, but when ready to resume
their flight they leave the river and fly directly south over the
more or less arid region that lies between the Arkansas and the Rio
Grande.


WIDE AND NARROW MIGRATION LANES

When birds start their southward migration, the movement necessarily
involves the full width of the breeding range. Later, there is a
convergence of the lines of flight taken by individual birds, owing
to the conformation of the land mass, and as the species proceeds
southward the width of the occupied region becomes less and less.
An example of this is provided by the common kingbird (_Tyrannus
tyrannus_), which breeds from Newfoundland to British Columbia, a
summer range 2,800 miles wide. On migration, however, its paths
converge, until in the southern part of the United States the
occupied area extends from Florida to the mouth of the Rio Grande,
a distance of only 900 miles, and still farther south the migration
path is further restricted. In the latitude of Yucatan it is not more
than 400 miles wide, and it is probable that the great bulk of the
species moves in a belt that is less than half that width.

A migration route, therefore, may be anything from a narrow path
that adheres closely to some definite geographical feature, such
as a river valley or a coast line, to a broad boulevard that leads
in the desired direction and follows only the general trend of the
land mass. Also it is to be remembered that whatever main routes are
described, there remain a multitude of tributary and separate minor
routes. In fact, with the entire continent of North America crossed
by migratory birds, the different groups or species frequently follow
lines that may repeatedly intersect those taken by others of their
own kind or by other species. The arterial routes, therefore, must
be considered merely as indicating paths of migration on which the
tendency to concentrate is particularly noticeable.

In considering the width of migration lanes it will be obvious that
certain species, as the knot (_Calidris canutus_) and the purple
sandpiper (_Arquatella maritima_), which are normally found only
along the coasts, must have extremely narrow routes of travel. They
are limited on one side by the broad waters of the ocean and on the
other by land and fresh water, both of which are unsuited to furnish
the food that is desired and necessary to the well being of these
species.

Among land birds that have a definite migration, the Ipswich sparrow
(_Passerculus princeps_) has what is probably the most rstricted
migration range of any species. It is known to breed only on Sable
Island, Nova Scotia, and it winters along the Atlantic coast south
to Georgia. Living constantly within sound of the surf, it is rarely
more than a quarter of a mile from the outer beach, and is entirely
at home among the sand dunes and their sparse covering of coarse
grass.

[Illustration: B4630M

Figure 16.--Breeding and wintering ranges and migration of Harris's
sparrow, an example of a narrow migration route through the interior
of the country. The heavy broken lines enclose the region traversed
by the majority of these finches; the light broken line encloses the
country where they occur with more or less regularity; while the
spots indicate records of accidental or sporadic occurrence.]

Harris's sparrow (_Zonotrichia querula_) supplies an interesting
example of a narrow migration route in the interior of the country
(fig. 16). This fine, large finch is known to breed only in the
region from Fort Churchill, on the west shore of Hudson Bay,
northwest to the shores of Great Bear Lake. Very few actual breeding
records of the species are available, but these are sufficient
to indicate that the breeding range is in the strip of country
characterized by more or less stunted timber just south of the limit
of trees. When it begins its fall migration, this bird necessarily
covers the full width of its breeding area. Then it proceeds almost
directly south, or slightly southeasterly, the area covered by the
majority of the species becoming gradually constricted, so that
by the time it reaches the United States it is most numerous in a
belt about 500 miles wide, extending across North Dakota to central
Minnesota. Harris's sparrows are noted on migration with fair
regularity east to the western shore of Lake Michigan, and west to
the foothills of the Rocky Mountains, but the great bulk of the
species moves north and south through a relatively narrow path in
the central part of the continent. Present knowledge suggests that
the reason for this narrow migration range is the close association
that Harris's sparrow maintains with a certain type of habitat,
including brushy places, thickets, edges of groves, and weed patches.
While these environmental conditions are found in other parts of
the country, the region crossed by this sparrow presents almost a
continuous succession of habitat of this type. Its winter range
extends from southeastern Nebraska and northwestern Missouri, across
eastern Kansas and Oklahoma and through a narrow section of central
Texas, at places hardly more than 150 miles wide.

[Illustration: B4502M

Figure 17.--Distribution and migration of the scarlet tanager.
During the breeding season individual scarlet tanagers may be 1,900
miles apart in an east-and-west line across the breeding range. In
migration, however, the lines converge until in southern Central
America they are not more than 100 miles apart. For migration paths
of other widths see figures 16, 18, and 19.]

The scarlet tanager presents another extreme case of narrowness of
migration route (fig. 17), its breeding range extending in greatest
width from New Brunswick to Saskatchewan, a distance of about 1,900
miles. As the birds move southward in fall their path of migration
becomes more and more constricted, until at the time they leave the
United States all are included in the 600-mile belt from eastern
Texas to the Florida peninsula. Continuing to converge through
Honduras and Costa Rica, the boundaries there are not more than 100
miles apart. The species winters in northwestern South America, where
it spreads out over most of Colombia, Ecuador, and Peru.

The rose-breasted grosbeak also leaves the United States through
the 700-mile stretch from eastern Texas to Appalachicola Bay, but
thereafter the lines do dot further converge, as this grosbeak enters
the northern part of its winter quarters in Central America and South
America through a door of about the same width (fig. 18).

[Illustration: B4501M

Figure 18.--Distribution and migration of the rose-breasted grosbeak.
Though the width of the breeding range is about 2,500 miles, the
migratory lines converge until the boundaries are only about 700
miles apart when the birds leave the United States. For migration
paths of other widths see figures 16, 17, and 19.]

While the cases cited represent extremes of convergence, a narrowing
of the migratory path is the rule to a greater or less degree for the
majority of North American birds. The shape of the continent tends to
effect this, and so the width of the migration route in the latitude
of the Gulf of Mexico is usually much less than in the breeding
territory.

The redstart (_Setophaga ruticilla_) represents a notable case of a
wide migration route, although even in the southern United States
this is much narrower than the breeding range (fig. 19). These birds,
however, cross all parts of the Gulf of Mexico and pass from Florida
to Cuba and Haiti by way of the Bahamas, so that here their route has
a width of about 2,500 miles.

[Illustration: B4500M

Figure 19.--Distribution and migration of the redstart. An example of
a wide migration route, since birds of this species cross all parts
of the Gulf of Mexico, or may travel from Florida to Cuba and through
the Bahamas. Their fly way thus has an east and west width of more
than 2,000 miles. For migration paths of greater or less extent see
figures 16, 17, and 18.]

In the following, the discussion of the principal routes of North
American birds relates chiefly to the fall migration, for, except
as otherwise noted, the spring flight generally retraces the same
course. The routes indicated on the maps (figs. 20 and 21) must not
be considered as representing paths with clearly defined borders, but
rather as convenient subdivisions of the one great flyway that covers
practically the entire width of the North American Continent and
extends from the Arctic coast to South America.

[Illustration: B1032M

Figure 20.--Principal migration routes used by birds in passing from
North America to winter quarters in the West Indies, Central America,
and South America. Route no. 4 is the one used most extensively; only
a few species make the 2,400-mile flight from Nova Scotia to South
America.]


ATLANTIC OCEANIC ROUTE

By reference to figure 20 it will be noted that route no. 1 is almost
entirely oceanic, passing directly over the Atlantic Ocean from
Labrador and Nova Scotia to the Lesser Antilles, and then through
this group of small islands to the mainland of South America. It is
not used by any of the smaller land birds, but is followed chiefly by
thousands of water birds and by shore birds of several species, the
adult golden plover being a notable example. Since it lies entirely
over the sea, this route is definitely known only at its terminals
and from occasional observations made on Bermuda and other islands in
its course. Some of the shore birds that breed on the Arctic tundras
of Mackenzie and in Alaska fly southeastward across Canada to the
Atlantic coast and finally follow the oceanic route to the mainland
of South America. The golden plover may accomplish the whole 2,400
miles without pause or rest, in fair weather the flocks passing
Bermuda and sometimes even the islands of the Antilles without
stopping. Although most birds make their migratory flights either by
day or by night, the golden plover in this remarkable journey flies
both day and night. As it swims lightly and easily it may make a few
short stops along the way, and it has been actually seen resting on
the ocean. Other shore birds have been observed busily feeding in
that great area of ocean known as the Sargasso Sea, where thousands
of square miles of floating seaweed teem with marine life.

[Illustration: B4767M

Figure 21.--Migration routes of North American birds. Though this
map was prepared chiefly to show the flyways used by waterfowl,
most of these routes also are utilized by innumerable land birds.
For example, the important Mackenzie Valley-Great Lakes-Mississippi
Valley route is shown (with its tributaries) from the Arctic coast to
the delta of the Mississippi River.]

[Illustration: B4768M

Figure 22.--Distribution and migration of the golden plover,
Pluvialis dominica. Adults of the eastern form (P. d. dominica)
migrate across northeastern Canada and then by a nonstop flight
reach South America. In spring they return by way of the Mississippi
Valley. Their entire route is therefore in the form of a great
ellipse with a major axis of 8,000 miles and a minor axis of about
2,000 miles. The Pacific golden plovers (P. d. fidva), which breed in
Alaska, apparently make a nonstop flight across the ocean to Hawaii,
the Marquesas Islands, and the Low Archipelago, returning in spring
over the same route.]

The annual flight of the adult golden plover is so wonderful that
it may be given in some detail, particularly since it is one of the
exceptions to the general rule that spring and fall movements are
over the same routes (fig. 22). After reaching the South American
const the birds make a short stop and then continue overland to the
pampas of Argentina, where they remain from September to March.
Leaving their winter quarters, they cross northwestern South America
and the Gidf of Mexico, reaching the North American mainland on
the coasts of Texas and Louisiana. Thence they proceed slowly up
the Mississippi Valley, and by the early part of June are again on
their breeding grounds, having performed a round-trip journey in the
form of an enormous ellipse with the minor axis about 2,000 miles
and the major axis 8,000 miles, reaching from the Arctic tundras to
the pampas of Argentina. The older birds are probably accompanied
by some of the young, perhaps those from early nestings, but most
of the immatures leave their natal grounds late in summer and move
southward through the interior of the country, re turning in spring
over essentially the same course. The elliptical route is therefore
used chiefly by fully adult birds.


ATLANTIC COAST ROUTE AND TRIBUTARIES

The Atlantic coast is a regular avenue of travel, and along it are
many famous points for observing both land and water birds. About 50
different kinds of land birds that breed in New England follow the
coast southward to Florida and travel thence by island and mainland
to South America (fig. 20, route 2). As will be seen from the map, a
seemingly natural and convenient highway extends through the Bahamas,
Cuba, Hispaniola, Puerto Kico, and the Lesser Antilles to the South
American coast. Resting places are afforded at convenient intervals,
and at no time need the aerial travelers be out of sight of land. It
is not, however, the favored highway, and only about 25 species of
birds go beyond Cuba to Puerto Rico along this route to their winter
quarters, while only 6 species are known to reach South America by
way of the Lesser Antilles. The obvious drawback is lack of adequate
food. The total area of all the West Indies east of Puerto Rico is
less than that of Rhode Island, so that if only a small part of
the birds of the eastern United States were to travel this way, it
is doubtful whether even the luxuriant flora and fauna of tropical
habitats would provide food sufficient for their needs.

In the northern part of the Atlantic coast route is a tributary route
used by the brant (_Branta bernicla_) that is of special interest.
The southward movement of these birds is chiefly along the western
shores of Hudson Bay and thence southeastward to the Atlantic coast.
Returning in spring, they follow the coast line north to the Gulf
of St. Lawrence and then fly almost due north to their breeding
grounds on the west coast of Greenland and the islands of the Arctic
archipelago. The round trip is therefore in the form of a great
ellipse, probably 3,000 miles long by 1,000 miles wide.

The Atlantic flyway receives accretions of waterfowl from three or
four interior migration paths, one of which is of first importance,
as it includes great flocks of canvasbacks (_Nyroca valisineria_),
redheads (_N. americana_), scaup ducks (_N. marila_ and _N.
affinis_), Canada geese, and many of the black ducks that winter
in the waters and marshes of the coastal region south of Delaware
Bay. The canvasbacks, redheads, and scaups come from their breeding
grounds on the great northern plains of central Canada, follow the
general southeasterly trend of the Great Lakes (fig. 21), cross
Pennsylvania over the mountains, and reach the Atlantic coast in the
vicinity of Delaware and Chesapeake Bays. Black ducks, mallards,
and blue-winged teals (_Querquedula discors_) that have gathered
in southern Ontario during the fall leave these feeding grounds
and proceed southwest over a course that is apparently headed for
the Mississippi Valley. Many do continue this route down the Ohio
Valley, but others, upon reaching the vicinity of Lake St. Clair,
between Michigan and Ontario, swing abruptly southeast and, crossing
the mountains in a single flight, reach the Atlantic coast south
of New Jersey. This route, with its Mississippi Valley branch, has
been fully demonstrated by the recovery records of ducks banded by a
cooperator of the Biological Survey at Lake Scugog, Ontario.

The white-winged scoter (_Melanitta deglandi_), which also breeds in
the interior country from northern North Dakota north to the Arctic
coast, is another bird having an elliptical migration route, so far
as those wintering on the Atlantic coast are concerned. This duck
breeds only near fresh water and winters entirely on the ocean along
both the Atlantic and Pacific coasts of the United States. Those
wintering on the Atlantic side leave their breeding grounds west of
Hudson Bay and fly 1,500 miles almost due east to the most eastern
part of Labrador, whence they proceed southward across the Gulf of
St. Lawrence to their winter home, which extends from southwestern
Maine to Chesapeake Bay. The spring flight is made by an interior
route that traverses the valleys of the Connecticut, Hudson, and
Ottawa Rivers, and thence passes west and north to the breeding
grounds.

A study of the Canada geese that winter abundantly in the waters of
Back Bay, Va., and Currituck Sound, N. C., reveals another important
tributary to the Atlantic coast route. Banding has shown that the
principal breeding grounds of these birds are among the islands and
on the eastern shores of Hudson Bay (fig. 21). From this region they
move south in fall to the point of lower Ontario between Lakes Erie
and Huron. Some of the banded geese are recovered in the Mississippi
Valley, but the great majority are retaken either on their breeding
grounds or on the Atlantic coast south of Delaware Bay, showing
another instance of a long cross-country flight by waterfowl.
Although Canada geese are abundant in migration on the coast of New
England, the birds taken there do not include any that were banded
in southern Ontario. Again, banding has shown that the New England
visitants come from other breeding areas, chiefly Newfoundland and
the desolate coast of Labrador, and that their migration is entirely
coastwise.

Still another cross-country route between the Mississippi Valley
and the Atlantic coast may be briefly described. While not yet
well understood, a hitherto unsuspected migration route across the
Alleghenies to the Mississippi Valley has been revealed by the
banding of blue-winged teal, on the coastal sawgrass marshes of
South Carolina. Birds marked in these marshes have been retaken in
Tennessee and Kentucky as well as in States farther north in the
Mississippi Valley. Several species of shoal-water ducks, including
this dainty little teal and the shoveler (_Spatula clypeata_), are
more or less common winter residents in the South Carolina marshes,
but are less common or even decidedly rare in most of the coastal
marshes farther north, so this cross-country route connecting two
main arteries of migration seems to be of considerable importance.

[Illustration: B4762M

Figure 23.--Distribution and migration of the bobolink. In crossing
to South America most of the bobolinks use route no. 3 (fig. 20),
directly from Jamaica across an unbroken stretch of ocean. Colonies
of these birds have established themselves in several areas in the
western United States, but in migration they adhere to the ancestral
fiyways and show no tendency to take the short cut across Arizona,
New Mexico, and Texas.]

Referring again to figure 20, it is noted that route no. 3 presents
a much more direct line of flight for the Atlantic coast migrants
to South America than the others, although it involves much longer
flights. It is used almost entirely by land birds. After taking off
from the coast of Florida the migrants find only two land masses on
the way where they can pause for rest and food. Nevertheless, tens
of thousands of birds of some 60 species cross the 150 miles from
Florida to Cuba, where about half of them elect to remain for the
winter. The others fly the 90 miles between Cuba and Jamaica. From
that point to the South American coast, however, there is a stretch
of unbroken ocean fully 500 miles across, and scarcely a third of
the North American migrants leave the forested mountains of Jamaica
to risk the perils of this ocean trip. Chief among those that do is
the bobolink (_Dolichonyx oryzivorus_), which so far outnumbers all
other birds using this fly way that route no. 3 may well be called
"the bobolink route" (fig. 23). As traveling companions along this
route the bobolinks may meet vireos, kingbirds, and nighthawks
from Florida; the chuck-will's-widow (_Antrostomus carolinensis_)
of the Southeastern States; black-billed and yellow-billed cuckoos
(_Coccyzus erythropthalmus_ and _C. americanus_) from New England;
gray-cheeked thrushes from Quebec, bank swallows (_Riparia riparia_)
from Labrador; and blackpoll warblers from Alaska. Sometimes this
scattered assemblage will be joined by a tanager or a wood thrush
but "the bobolink route" is not popular with the greater number of
migrants, and although many individuals traverse it, they are only a
small fraction of the multitudes of North American birds that spend
the winter in South America.


MACKENZIE VALLEY-GREAT LAKES-MISSISSIPPI VALLEY ROUTE AND TRIBUTARIES

Easily the longest flyway of any in the Western Hemisphere is that
extending from the Mackenzie Valley past the Great Lakes and down the
Mississippi River, including its tributaries. Its northern terminus
is on the Arctic coast in the regions of Kotzebue Sound, Alaska, and
the mouth of the Mackenzie River, while its southern end lies in
Patagonia (fig. 21). During the spring migration some of the shore
birds traverse the full extent of this great path, and it seems
likely that the nighthawk, the barn swallow, the blackpoll warbler,
and individuals of several other species that breed north to Yukon
and Alaska must twice each year cover the larger part of it.

For more than 3,000 miles--from the mouth of the Mackenzie to the
Delta of the Mississippi--this flyway is uninterrupted by mountains.
In fact, there is not even a ridge of hills on the route high
enough to interfere with the movements of the feathered travelers,
and the greatest elevation above sea level is less than 2,000
feet. Well timbered and watered, the entire region affords ideal
conditions for the support of its great hosts of migrating birds.
This route is followed by such vast numbers of ducks, geese, shore
birds, blackbirds, sparrows, warblers, and thrushes, that observers
stationed at favorable points in the Mississippi Valley during
the height of migration can see a greater number of species and
individuals than can be noted anywhere else in the world.

Starting in the region of Kotzebue Sound, Alaska, the route extends
eastward across northern Alaska and joins another that has its
origin at the mouth of the Mackenzie River (fig. 21). The line of
flight then trends a little east of south through the great lake
system of central Canada, where it is joined by 2 or 3 other routes
from the northeast that have their origin on the central Arctic
coast. Continuing southward the migrating flocks are constantly
augmented by additions to their numbers as they pass over the great
breeding grounds of central and southern Canada. Upon reaching the
headwaters of the Missouri and Mississippi Rivers the route follows
these streams to the Gulf coast. Arriving in this latitude many
species, including ducks and geese, the robin, the myrtle warbler,
and some others spread out east and west for their winter sojourn.
Others, despite the perils of a trip involving a flight of several
hundred miles across the Gulf of Mexico, strike out boldly for
Central America and South America. This part of the route is a broad
"boulevard" extending from northwestern Florida to eastern Texas
and reaching southward across the Gulf of Mexico to Yucatan and the
Isthmus of Tehuantepec (fig. 20, route 4).

Many of the birds that breed east of the Allegheny Mountains parallel
the sea coast as they move southwestward in fall and, apparently
maintaining the same direction from northwestern Florida, cross the
Gulf to the coastal regions of eastern Mexico. On the other hand,
the birds that have come south directly through the Mississippi
Valley and the region west to the Rocky Mountains reach the coastal
plains of Mississippi, Louisiana, and Texas and continue directly
across the Gulf. The great majority of North American birds seeking
winter homes in the Tropics thus elect the short cut across the
Gulf of Mexico in preference to the longer although safer land or
island journey by way of Texas or Florida. During the height of the
migration some of the islands off the coasts of Louisiana and Texas
are wonderful observation places for the student of birds, as the
feathered travelers literally swarm over them.

One of the short cuts (fig. 20, route 5) that may be considered a
part of this great water artery of migration extends a few hundred
miles from the coast of Texas to the northern part of the State
of Vera Cruz. As the neighboring coast is arid and thus entirely
unsuited to the needs of birds that are frequenters of moist
woodlands, it is not surprising to find that this Gulf route is used
by such woodland species as the golden-winged warbler (_Vermivora
chrysoptera_), the worm-eating warbler (_Helmitheros vermivorus_),
and the Kentucky warbler (_Oporornis formosus_).

Formerly it was thought that most of the North American birds
that migrate to Central America made a leisurely trip along the
Florida coast, crossed to Cuba, and thence made the short flight
from the western tip of Cuba to Yucatan. A glance at the map would
suggest this as a most natural route, but as a matter of fact it is
practically deserted except for a few swallows and shore birds, or an
occasional land bird storm-driven from its accustomed course.

Present knowledge of the chief tributaries to the Mackenzie
Valley-Great Lakes-Mississippi Valley highway relates chiefly to
waterfowl. Reference already has been made to the flight of the
black ducks (p. 42) that reach the Mississippi Valley from southern
Ontario. Some individuals of this species banded at Lake Scugog,
Ontario, have been recaptured in succeeding seasons in Wisconsin
and Manitoba, but the majority have been retaken at points south
of the junction of the Ohio River with the Mississippi, definitely
indicating their route of travel from southern Ontario.

A second route that joins the main artery on its eastern side is the
one used by the blue goose (fig. 10), the migration route of which
is probably more nearly due north and south than that of any other
North American bird. The breeding grounds, which only recently have
been discovered, are in the Fox Basin region of Baffin Island and
on Southampton Island. In fall these geese work southward, chiefly
along the eastern shore of Hudson Bay, and upon reaching the southern
extremity of James Bay they take off for what is practically a
nonstop flight to the great coastal marshes of Louisiana west of
the delta of the Mississippi River (fig. 21). In some seasons the
flocks make intermediate stops among the islands and sand bars of the
Mississippi, as they are occasionally common in the general vicinity
of Memphis, Tenn. Most of the birds push on, however, and during
the period from the first of November to the last of March fully
90 percent of the species are concentrated in the area between the
Sabine and the Mississippi Rivers. On the return trip northward there
is sometimes a tendency for some of the blue geese to veer off toward
the Northwest, as they are occasionally abundant in eastern South
Dakota and southeastern Manitoba. It is of particular interest to
note that while some other geese and many ducks start their northward
journey at the first sign of awakening spring, the blue goose remains
in its winter quarters until the season there is far advanced,
seemingly aware that its own breeding grounds in the Arctic are still
in the grip of winter.

As shown by the route map (fig. 21) a great western highway also has
its origin in the Mackenzie River delta area and in Alaska. This is
used chiefly by the pintail and the baldpate (Mareca americana),
which fly southward through eastern Alberta to western Montana. Some
localities in this area, as for example, the National Bison Range, at
Moiese, Mont., normally furnish food in such abundance as to induce
these birds to pause in their migratory movement. Upon resuming
travel, some flocks move almost directly west across Idaho to the
valley of the Columbia River, from which they turn abruptly south to
the interior valleys of California. Others leave the Montana feeding
and resting areas and turn southeastward across Wyoming and Nebraska
to join the flocks that either are moving southward through the Great
Plains, or are to continue across Arkansas to the main Mississippi
Valley fly way.

Many redheads that breed in the Bear River marshes in Utah, take a
westerly route across Nevada to California, but some leave these
breeding grounds and fly northeastward across North Dakota and
Minnesota to join the flocks of these ducks that come out of the
prairie regions of Canada, and travel southeastward to the Atlantic
coast. This route can be well traced by the records of ducks banded
in summer in the Bear River marshes and retaken the following fall
at points in eastern Montana, Wyoming, South Dakota, North Dakota,
Minnesota, Wisconsin, Michigan, and Maryland.

Another route from these great marshes crosses the mountains in an
easterly direction, but almost immediately turns southward through
Colorado and New Mexico, and continues to winter quarters in the
Valley of Mexico (fig. 21 and fig. 20, route 6). This route also
represents the travels of many of the land birds of the Rocky
Mountain region. Such birds perform comparatively short migrations,
most of them being content to stop when they reach the middle
districts of Mexico, only a few passing east beyond the southern part
of that country.

This account of the Mackenzie Valley-Great Lakes-Mississippi Valley
route shows the great importance of this highway and also its
complicated nature. It receives accretions from both the northeast
and the northwest, while branch routes make wide detours toward the
Pacific coast before turning back to the parent fly way. This flyway
is notable for its great length, as it extends from the Arctic-coast
to Patagonia; and for its width east and west, as in North America it
reaches from the Allegheny Mountains westward to the Great Basin.


PACIFIC COAST ROUTE

Although it does present features of unusual interest, the
Pacific-coast route is not of so great importance as some of the
others described. Because of the equable conditions that prevail,
many species of birds along the coast from the Northwestern States to
Southern Alaska either do not migrate at all or else make relatively
short journeys. This route has its origin chiefly in Alaska, the
general region of the delta of the Yukon River marking its northern
terminus, although a few species join it after a flight westward
along the Alaskan Arctic coast (fig. 21). Some of the scoters
(_Melanitta_ and _Oidemia_) and other sea ducks of the north Pacific
region, and the diminutive cackling goose (Branta canadensis minima),
which breeds in the delta of the Yukon River, use the coastal sea
route for all or most of their southward flight. The journey of
the cackling geese, as shown by return records from birds banded
at Hooper Bay, Alaska, has been traced southward across the Alaska
Peninsula and apparently across the Gulf of Alaska to the Queen
Charlotte Islands, the birds following the coast line south to near
the mouth of the Columbia River. There the route swings toward the
interior for a short distance before continuing south by way of the
Willamette River Valley. The winter quarters of the cackling geese
are chiefly in the vicinity of Tule Lake, on the Oregon-California
line, and in the Sacramento Valley of California, though a few push
on to the San Joaquin Valley.

[Illustration: B4509M

Figure 24.--Probable breeding range, the winter range, and the
migration route of Ross's goose. This is the only species of which
all members apparently breed in the Arctic regions, migrate south
through the Mackenzie Valley, and upon reaching the United States
turn to the southwest rather than the southeast. The southern part
of this route, however, is followed by some mallards, pintails,
baldpates, and possibly by other ducks.]

A tributary of this flyway is followed by Ross's goose (_Chen
rossi_), which is believed to breed on the Arctic islands north of
Mackenzie (fig. 24). Its fall migration is across the barren grounds
to Great Slave and Athabaska Lakes, where it joins thousands of other
waterfowl bound for their winter homes along the eastern coast of
the United States and the Gulf of Mexico. But when Ross's geese have
traveled south approximately to the northern boundary of Montana,
they separate from their companions, and turning to the southwest
cross the Rocky Mountains and settle for the winter in California.

The route taken by the white-winged scoters that winter on the
Atlantic coast already has been indicated (p. 43). Some birds of this
species, however, winter on the Pacific coast from Puget Sound south
to southern California. Their passage by thousands up and down the
coast has been noted as far north as northwestern British Columbia.
The species is known to nest in Alaska, which may be the home of
some at least of the scoters that winter on the Pacific coast. If
such be the case, however, it must be admitted that a part of the
route taken by the birds when on migration is unknown, though very
few observations are available from the interior of northern British
Columbia, across which the route may lie.

The southward route of those migratory land birds of the Pacific
coast that in winter leave the United States extends chiefly through
the interior of California to the mouth of the Colorado River and on
to winter quarters in western Mexico.

The movements of the western tanager (_Piranga ludoviciana_) show a
migration route that is in some ways remarkable. The species breeds
in the mountains from the northern part of Baja California and
western Texas north to northeastern British Columbia and southwestern
Mackenzie. Its winter range is in two discontinuous areas--southern
Baja California and eastern Mexico south to Guatemala (fig. 25). On
the spring migration the birds enter the United States about April
20, appearing first in western Texas and the southern parts of New
Mexico and Arizona (fig. 26). By April 30 the van has advanced evenly
to an approximate east-and-west line across central New Mexico,
Arizona, md southern California. But by May 10 the easternmost
birds have advanced only to southern Colorado, while those in the
far West have reached northern Washington. Ten days later the
northward advance of the species is shown as a great curve, extending
northeastward from Vancouver Island to central Alberta and thence
southeastward to northern Colorado. Since these tanagers do not reach
northern Colorado until May 20, it is evident that those present in
Alberta on that date, instead of traveling northward through the
Rocky Mountains, which from the location of their summer and winter
homes would seem to be the natural route, reached there by the
Pacific coast route to southern British Columbia and thence across
the mountains, despite the fact that these are still partly covered
with snow at that time.


PACIFIC OCEANIC ROUTE

The route of the Pacific golden plover (_Pluvialis dominica fulva_)
is fully as interesting and as remarkable as the elliptical course
followed by its eastern cousin (_P. d. dominica_) (fig. 22). The
breeding range of the eastern golden plover extends through Arctic
America west to the northern coast of Alaska, where in the vicinity
of Point Barrow it meets the nesting grounds of the Pacific form,
which is really an Asiatic subspecies. It breeds chiefly in the
Arctic coast region of Siberia and merely overflows onto the Alaskan
coast, some of the birds probably migrating south along the coast
of Asia to winter quarters in Japan, China, India, Australia, New
Zealand, and Oceania, including the Hawaiian Islands, the Marquesas
Islands, and the Low Archipelago. Golden plovers in migration have
been observed at sea on a line that apparently extends from these
islands to the Aleutians, and it therefore appears certain that
at least some of the Alaskan birds make a nonstop flight across a
landless sea from Alaska to Hawaii. While it would seem incredible
that any birds could lay a course so straight as to attain these
small oceanic islands, 2,000 miles south of the Aleutians, 2,000
miles west of Baja California, and nearly 4,000 miles east of Japan,
the evidence admits only the conclusion that year after year this
transoceanic round-trip journey between Alaska and Hawaii is made by
considerable numbers of golden plovers.

[Illustration: B4761M

Figure 25.--Breeding and wintering ranges of the western tanager. See
figure 26 for the spring route taken by the birds breeding in the
northern part of the range.]

[Illustration: B4499M

Figure 26.--Migration of the western tanager. The birds that arrive
in eastern Alberta by May 20 do not travel northward along the
eastern base of the Rocky Mountains, as in that region the van has
then only reached northern Colorado. Instead the isochronal lines
indicate that they migrate north through California, Oregon, and
Washington, and then cross the mountains of British Columbia.]

The Pacific oceanic route probably is used also by the arctic terns
that breed in Alaska, and possibly by those from the more western
tern colonies of Canada. This species is of regular occurrence on
the western coasts of both the United States and South America,
indicating that the western representatives travel southward to the
Antarctic winter quarters without the spectacular migration features
that appear to characterize the flight of those from the eastern part
of the continent (fig. 15).


ARCTIC ROUTES

In the discussion of the migration of the Arctic tern (p. 31) it was
noted that this species makes a very distinct west-to-east movement
across northern Canada, continning the flight eastward across
the Atlantic Ocean toward the western coast of Europe. It seems
likely that there are other species, including the parasitic jaeger
(_Stercorarius parasiticus_) that regularly breed in the northern
part of the Western Hemisphere but migrate back to the Old World
for their winter sojourn. Some others, as the red-legged kittiwake
(_Rissa brevirostris_) and Ross's gull (_Rhodostethia rosea_), remain
near the Arctic region throughout the year, retreating southward
in winter only a few hundred miles. The emperor goose _(Philacte
canagica_) in winter is found only a relatively short distance south
of its breeding grounds, and eider ducks (Somateria and Arctonetta),
although wintering in latitudes well south of the breeding grounds,
nevertheless remain farther north than do the majority of other
species of ducks (fig. 21).

The routes followed by these birds are chiefly coastwise, and in the
final analysis may be considered as being tributary either to the
Atlantic or to the Pacific coast routes. The passage of gulls, ducks,
and other water birds at Point Barrow, Alaska, and at other points
on the Arctic coast, has been noted by several observers, and from
present knowledge it may be said that the best defined Arctic route
in North America is the one that follows around the coast of Alaska.




=EVOLUTION OF MIGRATION ROUTES=


From the foregoing descriptions of migration routes it will be
observed that the general trend of migration in most species of North
American birds is northwest and southeast. It is comparatively easy
to trace the probable steps in the evolution of the migrations of
some species, and some routes have developed so recently that they
still plainly show their origin.

The tendency is for eastern species to extend their ranges by pushing
westward, particularly in the north. For example in the Stikine
River Valley of northern British Columbia and southwestern Alaska
the eastern nighthawk (_Chordeiles minor minor_), eastern chipping
sparrow (_Spizella passerina passerina_), rusty blackbird (_Euphagus
carolinus_), eastern yellow warbler (_Dendroica aestiva aestiva_),
redstart, and others have established breeding stations at points 20
to 100 miles from the Pacific Ocean. The robin, flicker (Colaptes
auratus), slate-colored junco (_Junco hyemalis hyemalis_), blackpoll
warbler, myrtle warbler (Dendroica coronata), and ovenbird (_Seiurus
aurocapillus_), all common eastern species, also are established as
breeding birds in western Alaska, the ovenbird having been detected
on the lower Yukon River. These birds, however, do not migrate in
fall by any of the Pacific routes, but instead retrace their journey
across the mountains and move southward along the broad flyways of
the interior.

The red-eyed vireo (_Vireo olivaceus_), a striking example of an
obundant woodland bird, is essentially an inhabitant of States
east af the Great Plains, but an arm of its breeding range extends
northwest to the Pacific coast in British Columbia (fig. 27). It
seems evident that this is a range extension that has taken place
comparatively recently by a westward movement from the upper Missouri
Valley, and that the invaders retrace in spring and fall the general
route by which they originally entered the country.

[Illustration: B4506M

Figure 27.--Distribution and migration of the red-eyed vireo. It is
evident that the red-eyed vireo has only recently invaded Washington
by an extension of its breeding range almost due west from the
upper Missouri Valley. Like the bobolink, however (fig. 23), the
western breeders do not take the short cut south or southeast from
their nesting grounds, but migrate spring and fall along the route
traversed in making this extension.]

In the case of the bobolink, a new extension of the breeding range,
and a consequent change in the migration of the species, has taken
place since the spread of settlement in this country (fig. 23). A
bird of damp meadows, it was originally cut off from the Western
States by the intervening arid regions. But with the advent of
irrigation and the bringing of large areas under cultivation, small
colonies of nesting bobolinks have appeared at various western
points, and now the species is established as a regular breeder
in the great mountain parks and irrigated valleys of Colorado and
elsewhere almost to the Pacific coast. In retracing their course
to reach the western edge of the route followed by the bulk of the
bobolinks that breed in the northern United States and southern
Canada, these western pioneers must fly long distances along a line
that runs almost due east and west.

Similarly it is possible to sketch what seems to be the logical
evolution of the remarkable routes of the golden plover (fig. 22). It
may be assumed that the eastern birds of this species first followed
an all-land route from the South American winter quarters through
Central America, Mexico, and Texas to the western parts of the
Mississippi Valley. As the migration route lengthened northward with
the retreat of the ice and the bird's powers of flight developed, it
would have a tendency to straighten the line and to shorten it by
cutting off some of the great curve through Mexico and Texas. First
a short flight across the western part of the Gulf of Mexico was
probably essayed. Proving successful, this was followed by flight
lines that moved farther east, until finally the roundabout curve
through Texas was entirely discarded and the flight made directly
across the Gulf to southern Louisiana.

As the great areas in Canada were gradually added to the bird's
domain, other important factors arose, the chief being the
attractiveness of the vast stretches of coast and plain of the
Labrador Peninsula, which in fall offered a bountiful store of
berries. The fall route therefore worked eastward to the Gulf of
St. Lawrence thence southwest through the interior to the coast
of Florida and across the Gulf of Mexico to the Central American
mainland. A series of shortening flights followed to take out the
great curve of the New England coast. A relatively short ocean flight
was probably attempted, say from Cape Cod to the Bahama Islands,
Cuba, and Jamaica, followed eventually by the long direct oceanic
route as it is now known.

As the Labrador Peninsula in spring is bound by frost and shrouded
by fog while the season advances rapidly through the interior, the
oceanic route proved useful only in fall, and the spring flight
continued through the Mississippi Valley. The above outline gives
a probable and fairly plausible explanation of the origin of this
wonderful route, particularly when it is remembered that migration
routes as now known are evolutions--age-long modifications of other
routes.

The evolution of the migration of the Pacific golden plover may be
explained in a similar fashion. At first the route probably followed
the Asiatic coast, through the Malay Peninsula and Oceania, thence
east in a great curve to the Low Archipelago, with individuals and
flocks dropping out to winter at many points along the way. The
Siberian birds probably continue to follow this ancient flyway,
but those nesting in Alaska began a long evolutionary series of
flights that cut down the length of their journey by shortening the
curve, until finally the transoceanic route of the present day was
developed.




=VERTICAL MIGRATION=


In the effort to find winter quarters furnishing satisfactory living
conditions, many North American birds fly hundreds of miles across
land and sea. Others, however, are able to attain their objective
merely by moving down the sides of a mountain. In such cases a
few hundred feet of altitude corresponds to hundreds of miles of
latitude. Movements of this kind, known as "vertical migrations", are
found wherever there are large mountain ranges. In the Rocky Mountain
region they are particularly notable, as chickadees, rosy finches
(_Leucosticte_), juncos, pine grosbeaks (_Pinicola_), and some other
species that nest in the Alpine Zone move down to the lower levels to
spend the winter. It has been noted that such species as Williamson's
sapsucker (Sphyrapicus thyroideus), and the western wood pewee
(_Myiochanes richardsoni_), which nest in the higher mountains, move
down to the lower regions in August following the breeding season.
At this time there is a distinct tendency also among the young of
mountain-breeding birds to work down to the lower levels as soon as
the nesting season is over. The sudden increases among birds in the
edges of the foothills are particularly noticeable when cold spells
with snow or frost occur at the higher altitudes.

Some species that normally breed in the Hudsonian or Arctic Zones
find suitable breeding areas on the higher levels of the mountains,
as for example the pipit, or titlark (_Anthus spinoletta rubescens_),
which breeds on the tundras of Alaska and northern Canada and also
south as far as Colorado on the summits of many peaks in the Rocky
Mountains. On the other hand a few species, as the Clark's crow, or
nutcracker (_Nucifraga columbiana_), nest at relatively low altitudes
in the mountains and as the summer advances move higher up, thus
performing a vertical migration that in a sense is comparable with
the post-breeding movements of herons on the Atlantic coast. These
illustrations show that the length of a migration route may depend
upon factors other than latitude.




=VAGRANT MIGRATION=


The most striking feature of the migrations of some of the herons
is a northward movement after the nesting season. The young of
some species commonly wander late in summer and in fall, sometimes
traveling several hundred miles north of the district in which they
were hatched. The little blue heron (_Florida caerulea caerulea_)
breeds commonly north to South Carolina, and by the last of July
the young birds begin to appear along the Potomac, Patuxent, and
Susquehanna Rivers, tributary to Chesapeake Bay. Although almost
all are immature individuals, as shown by their white plumage, an
occasional adult may be noted. With them come snowy herons (_Egretta
thula thula_) and egrets (_Casmerodius albus egretta_), and on
occasion all three species will travel in the East as far north as
New England, and in the Mississippi Valley to southeastern Kansas and
Illinois. In September most of them disappear, probably returning
south by the same route.

The black-crowned night heron (_Nycticorax nycticorax hoactli_) has
similar wandering habits, and young birds banded in a large colony
at Barnstable, Mass., have been recaptured the same season north
to Maine and Quebec and west to New York. This habit seems to be
shared by some of the gulls also, although here the evidence is not
so conclusive. Herring gulls (_Larus argentatus smithsonianus_)
banded as chicks at colonies in the Great Lakes have scattered in all
directions after the breeding season, some having been recovered well
north in Canada.

These movements may be considered as migration governed only by
the availability of food, and they are counteracted in fall by
a directive migratory impulse that carries back to their normal
winter homes in the south such birds as after the mating period have
attained more northern latitudes. They are not to be compared with
the great invasions of certain birds from the North. Classic examples
of the latter in the eastern part of the country are the periodic
flights of crossbills. Sometimes these migrations will extend well
south into the Carolinian Zone.

Snowy owls are noted for occasional invasions that probably are
caused by a shortage of the lemmings and rabbits that constitute
their normal food in the North. At least nine notable flights of
these birds occurred during the period 1876 to 1927. In the great
flight of 1926-27 they were noted as far south as Iowa, Ohio, West
Virginia, and North Carolina.

In the Rocky Mountain region great flights of the beautiful Bohemian
waxwing (_Bombycilla garrula pallidiceps_), are occasionally
recorded. The greatest invasion in the history of Colorado
ornithology occurred in February 1917, at which time the writer
estimated that at least 10,000 were within the corporate limits of
the city of Denver. The last previous occurrence of the species in
large numbers in that section was in 1908.

Evening grosbeaks (_Hesperiphona vespertina_) likewise are given to
performing more or less wandering journeys, and curiously enough,
in addition to occasional trips south of their regular range, they
travel east and west, sometimes covering long distances. For example,
grosbeaks banded at Sault Ste. Marie, Mich., have been recaptured on
Cape Cod, Mass., and in the following season have been re trapped
at the banding station. Banding records demonstrate that this
east-and-west trip across the northeastern part of the country is
sometimes made also by purple finches (_Carpodacus purpureus_).




=PERILS OF MIGRATION=


The period of migration is a season full of peril for birds. Untold
thousands of the smaller migrants are destroyed each year by storms,
in unfamiliar habitats, and through attacks of predatory birds,
mammals, and reptiles. If each pair of adult birds should succeed
in raising two fledglings to maturity, the population of migratory
birds would have a potential annual increase of 100 percent and the
world would soon be heavily overpopulated with them. It is evident,
therefore, that there is no such increase, and that the annual
mortality from natural causes is heavy enough to keep it in check.


STORMS

Of the various factors limiting the abundance of birds, particularly
the smaller species, storms are the most potent. Special sufferers
are those birds that in crossing broad stretches of water are forced
by a storm down within reach of the waves. Such a catastrophe was
once seen from the deck of a vessel in the Gulf of Mexico, 30 miles
off the mouth of the Mississippi River. Great numbers of migrating
birds, chiefly warblers, had accomplished nearly 95 percent of
their long flight and were nearing land when, caught by a norther,
against which they were unable to contend, hundreds were forced into
the waters of the Gulf and drowned. On another occasion, on Lake
Michigan, a severe storm, coming up at a time when large numbers
of migratory birds were crossing, forced numerous victims into the
waves. During the fall migration of 1906, when thousands of birds
were crossing Lake Huron, a sudden drop in temperature, accompanied
by a heavy snowfall, resulted in the death of incredible numbers.
Literally thousands were forced into the water and subsequently cast
up along the beaches, where in places their bodies were piled in
windrows. On one section of the beach the dead birds were estimated
at 1,000 per mile, and at another point at five times that number.
Most of them were species that rank among our most desirable birds as
destroyers of insects and weed seeds, including slate-colored juncos,
tree sparrows, white-throated sparrows, swamp sparrows, winter wrens,
and golden-crowned kinglets, together with many brown creepers,
hermit thrushes, warblers, vireos, and others.

Of all species of North American birds, the Lapland longspur
(_Calcarius lapponicus_) seems to be the most frequent victim of
mass destruction from storms. These birds sometimes congregate in
enormous numbers where grass or weed seed is abundant. Almost every
winter brings in reports of their death by thousands somewhere in the
Middle West. While migrating northward at night they have encountered
blinding storms of wet, clinging snow, which have so bewildered
them that they have flown into various obstructions, or have sunk
to the ground and perished of exposure and exhaustion. In 1907 an
experienced ornithologist estimated that 750,000 longspurs were lying
dead on the ice of two lakes in Minnesota, each about 1 square mile
in extent, and dead birds were reported in greater or less abundance
on this occasion over an area of more than 1,500 square miles. The
heaviest mortality occurred in towns, where, bewildered by the
darkness and the heavy falling snow, some of the birds congregating
in great numbers, flew against various obstacles and were killed or
stunned, while many others fell to the ground exhausted. Similar
catastrophes have been reported from eastern Colorado, Nebraska, and
North Dakota.

During the early part of June 1927, a hailstorm of exceptional
severity in and around Denver, Colo., killed large numbers of robins,
meadow larks, sparrows, and others. The lawns of parks were strewn
with the bodies of these birds, and many lay dead in their nests
where they were covering their eggs or young when the storm broke.


AERIAL OBSTRUCTIONS

The destruction of migratory birds by their striking lighthouses,
light ships, tall bridge piers, monuments, and other obstructions
has been tremendous. Beams of the lanterns at light stations have
a powerful attraction for nocturnal travelers of the air. It may
be likened to the fascination for lights that is shown by many
insects, particularly night-flying moths. The attraction is not so
potent in clear weather, but when the atmosphere is moisture laden,
as in a heavy fog, the rays have a dazzling effect that lures the
birds to their death. They may fly straight up the beam and dash
themselves headlong against the glass, or they may keep fluttering
around the source of the light until exhausted, and then drop
to the rocks or waves below. The fixed, white, stationary light
located 180 feet above sea level at Ponce de Leon Inlet (formerly
Mosquito Inlet), Fla., has caused great destruction of bird life
even though the lens is shielded by wire netting. On one occasion an
observer gathered up a bushel-basketful of warblers, sparrows, and
other small passerine birds that had struck during the night. The
birds apparently beat themselves to death against the wire or fell
exhausted to the concrete pavement below, frequently to be destroyed
there by cats or skunks. Two other lighthouses at the southern end
of Florida, Sombrero Key and Fowey Rocks, have been the cause of
a great number of bird tragedies, while heavy mortality has been
noted also At some of the lights on the Great Lakes and on the coast
of Quebec. It is the fixed white lights that cause such disasters
to birds, as the stations equipped with flashing or red lights do
not present such strong attractions. That it is not a mere case of
geographical location has been demonstrated, for it is observed that
when fixed white lights have been changed to red or flashing lights,
the migrating birds are no longer endangered. At some of the light
stations in England and elsewhere, shelves and perches have been
placed below the lanterns to afford places where birds can rest until
they have overcome their bewilderment.

For many years at the National Capital, the Washington Monument,
although unilluminated, caused the destruction of large numbers of
small birds, due apparently to their inability to see this obstacle
in their path, towering more than 555 feet into the air. One morning
in the spring of 1902 the bodies of nearly 150 warblers, sparrows,
and other birds were found about its base. Then, as the illumination
of the city was improved and the Monument became more visible at
night, the loss became steadily less, until by 1920 only a few birds
would be killed during an entire migration. On November 11, 1931,
however, as part of the Armistice Day celebration, batteries of
brilliant floodlights grouped on all four sides about the base of the
Monument, were added to the two searchlights already trained on the
apex, so that the lighted shaft probably corresponded in brilliancy
to a very low magnitude lighthouse lantern. Airplane pilots have
ventured opinions that on a clear night it could be seen for 40
miles. It is certain that there is an extensive area of illumination,
and on clear, dark nights when the nocturnal travelers seem to fly at
lower altitudes, many of them are attracted to the Monument as to a
lighthouse beacon, and wind currents prevent a last-minute avoidance.
During the fall migration of 1932 more than 500 warblers, vireos,
thrushes, kinglets, sparrows, and others were killed. In 1933 the
mortality was less, but the Monument at times still remains a serious
menace to birds during migration.

When the torch on the Statue of Liberty in New York Harbor was kept
lighted, it caused an enormous destruction of bird life, tabulations
showing as many as 700 birds in a single month.


EXHAUSTION

Although it would seem that the exertion incident to the long
flights of many species of migratory birds would result in their
arrival at their destination in a state bordering on exhaustion,
this is contrary to the truth. Both the soaring and the sailing of
birds show them to be proficient in the use of factors employed in
aerial transportation that only recently have become understood and
imitated by aeronautical engineers. The use of ascending currents
of air, employed by all soaring birds, and easily demonstrated by
observing the gulls that glide hour after hour along the windward
side of a ship, are now utilized by man in his operation of gliders.
Moreover, the whole structure of a bird renders it the most perfect
machine for extensive flight that the world has ever known. Hollow,
air-filled bones, making an ideal combination of strength and
lightness, and the lightest and toughest material possible for
flight in the form of feathers, combine to produce a perfect flying
machine. Mere consideration of a bird's economy of fuel or energy
also is enlightening. The golden plover, traveling over the oceanic
route, makes the entire distance of 2,400 miles from Nova Scotia to
South America without stop, probably requiring about 48 hours of
continuous flight. This is accomplished with the consumption of less
than 2 ounces of fuel in the form of body fat. To be as economical in
operation, a 1,000-pound airplane would consume in a 20-mile flight
not the gallon of fuel usually required, but only a single pint.

The sora, or Carolina rail (_Porzana Carolina_), which is such a
notoriously weak flyer that at least one writer was led to infer
that most of its migration was made on foot, has one of the longest
migration routes of any member of its family, and easily crosses the
wide reaches of the Caribbean Sea. The tiny ruby-throated hummingbird
(_Archilochus colubris_) crosses the Gulf of Mexico in a single
flight of more than 500 miles.

While birds that have recently arrived from a protracted flight over
land or sea sometimes show evidences of being tired, their condition
is far from a state of exhaustion, unless unusual conditions have
been encountered, and with a few hours' rest and a crop well filled
with proper food they exhibit eagerness to resume their journey. The
popular notion that birds find the long ocean flights excessively
wearisome and that they sink exhausted when terra firma is reached
does not agree with the facts. The truth lies in the opposite
direction, as even small land birds are so little averse to ocean
voyages that they not only cross the Gulf of Mexico at its widest
point, but may even pass without pause over the low, swampy coastal
plain to the higher regions beyond. Under favorable conditions birds
can fly when, where, and how they please. Consequently the distance
4 covered in a single flight is governed chiefly by the food supply.
Exhaustion, except as the result of unusual factors, cannot be said
to be an important peril of migration.




=INFLUENCE OF THE WEATHER ON MIGRATION=


The state of the weather at any point has little if anything to do
with the time of arrival of migratory birds. This is contrary to the
belief of observers who have thought that they could foretell the
appearance of various species by a study of the weather conditions.
Though the insistent crescendo note of the ovenbird is ordinarily
associated with the full verdure of May woods, this bird has been
known to reach its breeding grounds in a snowstorm and the records of
its arrival in southern Minnesota show a temperature variation from
near freezing to full summer warmth. Temperatures recorded at the
time of arrival of several other common birds show variations of 14°
to 37° F., the average variation being about 24°.

It should be remembered that North American species spending the
winter months in tropical latitudes experience no marked changes in
climatic conditions from November to March or April, yet frequently
they will start the northward movement in January or February. This
is in obedience to physiological promptings and has no relation to
the prevailing weather conditions. For migratory birds the winter
season is a period of rest, a time when they have no cares other
than those associated with the daily search for food or escape from
their natural enemies. Their migrations, however, are a vital part
of their life cycles, which have become so well adjusted that the
seasons of travel correspond in general with the major seasonal
changes on their breeding grounds. With the approach of spring,
therefore, the reproductive impulse awakens, and each individual bird
is irresistibly impelled to start the journey that ends in its summer
home.

Through their influence upon the food supply, weather conditions in
the breeding areas do, of course, figure prominently in the picture.
In fact, they are the major factors in determining the average
dates of arrival of the different species. The word "average" must
be emphasized, for the migrations of birds have so evolved that in
general they synchronize with average climatic conditions. In other
words, migration is so ingrained that each species moves north in
spring when the average weather that will be encountered is not
unendurable. The hardy birds travel early, fearless of the blasts
of retreating winter. The more delicate species come later, when
there is less danger of encountering prolonged periods of inclement
weather. Some of these hardy birds pause and allow the spring season
to advance, and then by rapid travel again overtake it, or in some
cases actually outstrip it. At times this results in some hardship
and occasionally in the destruction of large numbers of individuals,
as has happened when early migrating bluebirds have been overwhelmed
by a late winter storm. Unless such conditions are prolonged,
however, no serious effect on the species is noted. Nevertheless,
the soundness of the bird's instincts is evidenced by the fact that
natural catastrophes, great though they may be, do not permanently
diminish the avian population.

As has been pointed out, the advance of average temperature lines,
known as isotherms, is found to correspond closely with the northward
movements of certain species. For example, the northward travels
of the Canada goose are found to coincide with the advance of the
isotherm of 35° F. (fig. 8).

The spring flight of migrants, if interrupted for any reason, is
resumed when weather conditions again become favorable, and it is
probable that all instances of arrival of birds in stormy weather
can be explained on the theory that the flight was begun while the
weather was auspicious. The state of the weather when a flight starts
at any southern point, the relation of that place to the average
position of the bird under normal weather conditions on that date,
and the average rate of migratory flight, are data basic to any
reasonably accurate prediction of the time arrival may be expected in
northern areas.

Head winds are as unfavorable to migration as is rain or snow, as
they greatly increase the labor of flight and cut down the speed of
cross-country travel. If such winds have a particularly high velocity
they may force down the weaker travelers, and should this happen over
water areas, large numbers of birds would be lost. Even strong winds
that blow in the direction of aerial travel are unfavorable for the
birds, as they interfere with their balance and disarrange their
feathers. Moderate tail winds and cross or quartering breezes appear
to offer the best conditions for the passage of the migrants.

[Illustration: B3712M

Figure 28.--A banded belted kingfisher, one of about 2,000,000 birds
that have been marked with Biological Survey bands.]




=PROBLEMS OF MIGRATION=


BANDING STUDIES

The study of living birds by the banding method, whereby great
numbers of individuals are marked (fig. 28) with numbered aluminum
leg rings, has come to be recognized as a most accurate means of
ornithological research. Since 1920, banding work in North America
has been under the direction of the Bureau of Biological Survey,
in cooperation with the National Parks Branch of Canada. Every
year volunteer cooperators, working under permit, place bands on
thousands of birds, game and nongame, large and small, migratory and
nonmigratory, each band carrying a serial number and the legend,
NOTIFY BIOLOGICAL SURVEY, WASHINGTON, D. C., or on the smaller sizes,
NOTIFY BIOL. SURV., WASH., D. C. When a banded bird is reported from
a second locality, a delinite fact relative to its movements becomes
known, and a study of many cases of this nature develops more and
more complete knowledge of the details of migration.

The records of banded birds are also yielding other pertinent
information relative to their migrations, such as the exact dates
of arrival and departure of individuals, the length of time that
different birds pause on their migratory journeys to feed and rest,
the relation between weather conditions and the starting times for
migration, the rates of travel of individual birds, the degree of
regularity with which birds return to the exact summer or winter
quarters used in former years, and many other details that could
be learned in no other manner. Banding stations that are operated
systematically throughout the year, therefore, are supplying much
information concerning the movements of migratory birds that
heretofore could only be surmised.


MOVEMENTS OF RESIDENTS

Typical migration consists of definite movements that are repeated
regularly year after year, and it is to these that the term is
generally restricted. It is desirable, however, if only for purposes
of comparison, that some account be taken of the movements of some
other birds, which, while not typical, do possess some of the
characteristics of true migration. Data on this subject are being
collected through bird banding.

There are several species that are customarily grouped under the
heading "permanent residents", the term implying that these birds
do not travel but remain throughout the year in one locality. Among
these are the cardinal, the tufted titmouse (_Baeolophus bicolor_),
the wren tit (_Chamaea jasciata_), the Carolina wren, the house
finch (_Carpodacus mexicanus frontalis_), the bobwhite (_Colinus
virginianus_), the California quail (_Lophortyx californica_), and
the ruffed grouse (_Bonasa umbellus_). Each species may be present
constantly throughout the year, although in the northern part of the
range there is probably a slight withdrawal of the breeding birds
in winter. The individuals to be seen at that season, therefore,
may not always be the same as those observed during the summer. It
is certain, however, that these species do not regularly perform
extensive journeys.

While the blue jay is disposed to be secretive, it is such a showy
and noisy bird that is not likely to escape notice. In the vicinity
of Washington, D. C., as in many other places, it is present the
year round, but at the end of September or early in October when
the weather is becoming cooler, troops of jays are sometimes seen
working southward through the trees. A corresponding northward
movement occurs again in May. This is unquestionably a migration to
and from some winter range, but its extent or significance is not now
known. Some light is being shed on the matter, however, through the
records of banded birds, and these eventually will fill in a more
perfect picture of the movements of this species. One jay, banded on
September 14, 1923, at Waukegan, Ill., was killed at Peruque, Mo.,
on November 15 of the same year; another, banded at Winnetka, Ill.,
on June 16, 1925, was retaken at Sulphur Kock, Ark., the following
December 10; a third, banded on May 6, 1925, at Whitten, Iowa, was
recaptured at Decatur, Ark., on January 22, 1926. These three birds
unquestionably had made a flight that had every appearance of being a
true migration to winter quarters in Missouri and Arkansas.

The black-capped chickadee is apparently resident in many places, but
occasionally in winter it invades the range of the southern Carolina
chickadee (_Penthestes carolinensis_) and in northern Canada it is
regularly a migrant.

In the coastal plain between Washington, D. C., and the Atlantic
Ocean, the white-breasted nuthatch is usually absent during the
summer, nesting at that season in the higher, or piedmont, country.
Late in fall, however, it appears in fair abundance in the wooded
bottoms, remaining at the lower levels until the following March or
April.

Some birds, including the screech owl (_Otus asio_), bobwhite,
Carolina wren, and mockingbird (_Mimus polyglottos_), seem to
be actually sedentary, but even these are sometimes given to
post-breeding wanderings. Ordinarily bob whites that are marked with
numbered bands are seldom retaken far from the area where banded, but
sometimes they will travel 10 miles or more. A screech owl banded
at Glenwood, Minn., in March, was recovered the following December
at Emmetsburg, Iowa, 180 miles south. Such flights, however, are
probably more in the nature of a search for new feeding areas, or to
escape from a winged enemy, than a true migratory journey.


MIGRATION OF THE WHITE-THROATED SPARROW

The white-throated sparrow (_Zonotrichia albicollis_) (fig. 29), one
of the most abundant members of its family, breeds from northern
Mackenzie and the southern part of the Ungava Peninsula south to
southern Montana, northern Pennsylvania, and Massachusetts. The
winter range extends from the southern part of the breeding range
south to the Gulf coast and northeastern Mexico. It is therefore a
common migrant in many sections. Since it is a ground-feeding bird
and is readily attracted to the vicinity of dwellings, it has been
banded in large numbers, the total to February 1, 1935, being nearly
100,000. It would be expected that these would yield a comparable
number of return records, and that the facts would furnish basic data
relative to the migrations of the species. Such, however, is not
the case. Banded white-throated sparrows are rarely recaptured at
stations between the breeding and the wintering grounds. Operators of
stations in the winter area, as Thomasville, Ga., and Summerville,
S. C., have obtained return records showing that these birds do come
back to the exact winter quarters occupied in previous seasons. The
fact that they do not again visit banding stations on their migration
routes indicates some unusual aspects of their travels, which it is
hoped will eventually be discovered by banding studies. Problems
of this type constitute definite challenges to the student of bird
migration.


MIGRATION OF THE YELLOW-BILLED LOON

The semiannual movements of the yellow-billed loon present an unusual
problem in migration. It breeds along the Arctic coast, probably
from Cape Prince of Wales eastward to Franklin Bay, and also in the
interior of northern Canada south to Clinton-Colden, Aylmer, and
Artillery Lakes, where it is rather common. It has been reported
as already present by May 25 at the mouth of the Liard River, in
southwestern Mackenzie. This coincides with the time that first
arrivals are noted fully 700 miles north, at Point Barrow, Alaska.
The problem has been to ascertain the route used by these birds to
then principal nesting grounds in the interior.

For a long time it was believed that this big diver did not winter in
large numbers anywhere on the Pacific coast, and it had been supposed
that the spring route extended 2,000 miles northeastward from a
wintering ground somewhere in eastern Asia to Bering Strait, then 500
miles still northeast to round Point Barrow, then 500 miles east to
the coast of Mackenzie, and finally 700 miles south--in spring--to
the region near the eastern end of Great Slave Lake.

The yellow-billed loon is a powerful flier, and it is probable that
this suggested route is correct for those birds that breed in the
northern coastal regions. A reasonable doubt may be entertained,
however, whether the breeding birds of Great Slave Lake and
contiguous areas reach their breeding grounds by the 700-mile flight
south from the Arctic coast. Within recent years it has been found
that these birds are fairly common in the maze of channels and
islands off the coast of southeastern Alaska as late as the last of
October and in February. Possibly they are present there during the
period from November through January also, or they may at that time
move farther offshore and so escape detection. If this region is an
important wintering ground, as seems probable, then it is likely that
the breeding birds of the interior reach their nesting grounds by
a flight eastward across the mountains, a trip that is well within
their flying ability, rather than by a circuitous route around the
northern coast. The air-line distance from southeastern Alaska to the
mouth of the Liard River is in fact less than the distance to that
point from the mouth of the Mackenzie.

[Illustration: B2216M

Figure 29.--White-throated sparrow, a bird that apparently breeds
and winters each year in the same areas, but either travels by
different routes or, at least, does not make the same stops, while on
migration.]

Differing routes to various parts of a large breeding or wintering
ground, and used by large groups of individuals of other species,
are not unknown. For example, the redhead duck is one of the common
breeding ducks of the Bear River marshes of Utah, where a great many
have been banded each summer. The recovery records of banded redheads
show that while many travel westward to California, others start
their fall migration in the opposite direction and, flying eastward
across the Rocky Mountains, either turn southeast across the plains
to the Gulf of Mexico, or deliberately proceed in a northeasterly
direction to join the flocks of this species moving toward the
Atlantic coast from the prairie regions of southern Canada.




=CONCLUSIONS=


The migration of birds as it is known today had its beginning in
times so remote that its origins have been entirely obscured, and
it can be interpreted now only in terms of present conditions. The
causes underlying migration are exceedingly complex. The mystery
that formerly cloaked the periodic travels of birds, however, has
been largely dispelled through the fairly complete information that
is now available concerning the extent and times of the seasonal
journeys of most of the species. Many gaps, however, still remain
in our knowledge of the subject. Much has been learned, and present
knowledge is being placed on record, but it must be left to future
study to clear away many of the uncertainties that continue to make
bird migration one of the most fascinating subjects in the science of
ornithology.

Each kind of bird seems to have its own reaction to its environment,
so that the character of movement differs widely in the various
species, and seldom do any two present the same picture. In
fact, bird migration has been described as a phase of geographic
distribution wherein there is a more or less regular seasonal
shifting of the avian population caused by the same factors that
determine the ranges of the sedentary species. If this view is
correct, then it must be recognized that the far-reaching works of
man in altering the natural condition of the earth's surface can so
change the environment necessary for the well being of the birds as
to bring about changes in their yearly travels. The nature and extent
of the changes wrought by man on the North American Continent are
easily apparent. Forests have been extensively cut away and their
places have been taken by second growth or cultivated land, and wide
stretches of prairie and plain have been broken up, irrigated, and
devoted to agriculture. These great changes are exerting a profound
effect upon the native bird populations, and the various species may
be either benefited or adversely affected thereby.

The Federal Government, has recognized its responsibility to the
migratory birds under changing conditions brought about by man, and
by enabling acts for carrying out treaty obligations, it is now
giving many important species legal protection under regulations
administered by the Bureau of Biological Survey. Much is being done
by legislation for the welfare of the birds. The effectiveness of
these conservation laws, however, is increased in the same measure
that the people of the country become acquainted with the facts
in the life histories of the migrants and interest themselves
personally in the well being of the various species. Long before the
white man came to America the birds had established their seasonal
lanes of migration throughout the Western Hemisphere, as here
outlined. The economic, inspirational, and esthetic values of these
migratory species dictate that they be permitted to continue their
long-accustomed and still mysterious habits of migration from clime
to clime.




=BIBLIOGRAPHY=[4]

[Footnote 4: Since almost every faunal paper on birds has a bearing
on the subject of migration, only a few can be listed in this
publication. Those included were selected to aid the student wishing
to pursue the subject further and to cover not only all cited in the
text but also others consulted and used in its preparation.]


(1) Allard, H. A.

  1928. BIRD MIGRATION FROM THE POINT OF VIEW OF LIGHT AND LENGTH OF
       DAY CHANGES. Amer. Nat. 62: 385-408.

(2) Austin, O. L., Jr.

  1928. MIGRATION-ROUTES OF THE ARCTIC TERN (STERNA PARADISAEA
       BRUNNICH). Northeastern Bird Banding Assoc. Bull. 4: 121-125.

(3) Baird, S. F.

  1866. THE DISTRIBUTION AND MIGRATIONS OF NORTH AMERICAN BIRDS.
       Amer. Jour. Sci. (2) 41: 78-90, 184-192, 337-347.

(4) Clarke, W. E.

  1912. STUDIES IN BIRD MIGRATION. 2 V., illus. London.

(5) Cooke, W. W.

  1888. REPORT ON BIRD MIGRATION IN THE MISSISSIPPI VALLEY IN THE
       YEARS 1884 AND 1885. U. S. Dept. Agr., Div. Econ. Ornith.
       Bull. 2, 313 pp., illus.

(6) ------------

  1904. DISTRIBUTION AND MIGRATION OF NORTH AMERICAN WARBLERS. U. S.
       Dept. Agr., Div. Biol. Survey Bull. 18, 142 pp.

(7) ------------

  1904. THE EFFECT OF ALTITUDE ON BIRD MIGRATION. Auk 21: 338-341

(8) ------------

  1905. ROUTES OF BIRD MIGRATION. Auk 22: 1-11.

(9) ------------

  1905. THE WINTER RANGES OF THE WARBLERS (MNIOTILTIDAE). Auk 22:
       296-299.

(10) ------------

  1906. DISTRIBUTION AND MIGRATION OF NORTH AMERICAN DUCKS, GEESE,
       AND SWANS. U. S. Dept. Agr., Bur. Biol. Survey Bull. 26, 90 pp.

(11) ------------

  1908. AVERAGING MIGRATION DATES. Auk 25: 485-486.

(12) ------------

  1910. DISTRIBUTION AND MIGRATION OF NORTH AMERICAN SHOREBIRDS. U.
       S. Dept. Agr., Bur. Biol. Survey Bull. 35, 100 pp., illus.

(13) ------------

  1913. DISTRIBUTION AND MIGRATION OF NORTH AMERICAN HERONS AND THEIR
       ALLIES. U. S. Dept. Agr., Bur. Biol. Survey Bull. 45, 70 pp.,
       illus.

(14) ------------

  1913. THE RELATION OF BIRD MIGRATION TO THE WEATHER. Auk 30:
       205-221, illus.

(15) ------------

  1914. DISTRIBUTION AND MIGRATION OF NORTH AMERICAN RAILS AND THEIR
       ALLIES. U. S. Dept. Agr. Bull. 128, 50 pp., illus.

(16) ------------

  1915. BIRD MIGRATION. U. S. Dept. Agr. Bull. 185, 47 pp., illus.

(17) ------------

  1915. BIRD MIGRATIONS IN THE MACKENZIE VALLEY. Auk 32: 442-459,
       illus.

(18) ------------

  1915. DISTRIBUTION AND MIGRATION OF NORTH AMERICAN GULLS AND THEIR
       ALLIES. U. S. Dept. Agr. Bull. 292, 70 pp., illus.

(19) Cooke, W. W.

  1915. THE YELLOW-BILLED LOONI A PROBLEM TN MIGRATION. Condor 17:
       213 214.

(20) Coues, E.

  1878. BIRDS OF THE COLORADO VALLEY, A REPOSITORY OF SCIENTIFIC AND
       POPULAR INFORMATION CONCERNING NORTH AMERICAN ORNITHOLOGY. U.
       S. Dept. Int. Misc. Pub. 11, 807 pp., illus.

(21) Gätke, H.

  1895. HELIGOLAND AS AN ORNITHOLOGICAL OBSERVATORY, THE RESULTS
       OF FIFTY YEARS' EXPERIENCE. (Transl. from the German by R.
       Rosenstock.) 599 pp., illus. Edinburgh.

(22) GRINNELL, J.

  1931. SOME ANGLES IN THE PROBLEM OF BIRD MIGRATION. Auk 48: 22—32.

(23) Gross, A. O.

  1927. THE SNOWY OWL MIGRATION OF 1926-27. Auk 44: 479-493, illus.

(24) Harrison, T. H.

  1931. ON THE NORMAL FLIGHT SPEEDS OF BIRDS. Brit. Birds 25: 86-96.

(25) Lincoln, F. C.

  1917. BOHEMIAN WAXWING (BOMBYCILLA GARRULA) IN COLORADO. Auk 34:
       341.

(26) ------------

  1922. TRAPPING DUCKS FOR BANDING PURPOSES: WITH AN ACCOUNT OF THE
       RESULTS OBTAINED FROM ONE WATERFOWL STATION. Auk 39: 322-334,
       illus.

(27) ------------

  1924. BANDING NOTES ON THE MIGRATION OF THE PINTAIL. Condor 26:
       88-90.

(28) ------------

  1924. RETURNS FROM BANDED BIRDS, 1920 TO 1923. U. S. Dept. Agr.
       Bull. 1268, 56 pp., illus.

(29) ------------

  1926. THE MIGRATION OF THE CACKLING GOOSE. Condor 28: 153-157,
       illus.

(30) ------------

  1927. NOTES ON THE MIGRATION OF YOUNG COMMON TERNS. North eastern
       Bird Banding Assoc. Bull. 3: 23-28, illus.

(31) ------------

  1927. RETURNS FROM BANDED BIRDS, 1923 TO 1926. U. S. Dept. Agr.
       Tech Bull. 32, 95 pp., illus.

(32) ------------

  1928. THE MIGRATION OF YOUNG NORTH AMERICAN HERRING GULLS. Auk 45:
       49-59.

(33) ------------

  1934. THE WATERFOWL FLYWAYS OF NORTH AMERICA. U. S. Dept. Agr.
       Circ. 342, 12 pp., illus.

(34) Magee, M. J.

  1928. EVENING GROSBEAK RECOVERIES. Northeastern Bird Banding Assoc.
       Bull. 4: 56-59.

(35) May, J. B.

  1929. RECOVERIES OF BLACK-CROWNED NIGHT HERONS BANDED IN
       MASSACHUSETTS. Northeastern Bird Banding Assoc. Bull. 5: 7-16,
       illus.

(36) Palmén, J. A.

  1893. REPORT ON THE MIGRATION OF BIRDS. Transl. from the German
       by C. W. Shoemaker. Smithsn. Inst. Ann. Rept. 1892: 375-396,
       illus.

(37) Phillips, J. C, and Lincoln, F. C.

  1930. AMERICAN WATERFOWL: THEIR PRESENT SITUATION AND THE OUTLOOK
       FOR THEIR FUTURE. 312 pp., illus. Boston and New York.

(38) Rowan, W.

  1925. RELATION OF LIGHT TO BIRD MIGRATION AND DEVELOPMENTAL
       CHANGES. Nature [London] 115: 494-495.

(39) ------------

  1926. ON PHOTOPERIODISM, REPRODUCTIVE PERIODICITY, AND THE ANNUAL
       MIGRATIONS OF BIRDS AND CERTAIN FISHES. Boston Soc. Nat. Hist.
       Proc. 38: [147]-189.

(40) Rowan, W.

  1930. EXPERIMENTS IN BIRD MIGRATION. II. REVERSED MIGRATION. Natl.
       Acad. Sci. Proc. 16: 520-525.

(41) ------------

  1930. THE MECHANISM OF BIRD MIGRATION. Sci. Prog. 25: 70-78.

(42) ------------

  1931. THE RIDDLE OF MIGRATION. 151 pp., illus. Baltimore.

(43) Watson, J. B., and Lashley, K. S.

  1915. AN HISTORICAL AND EXPERIMENTAL STUDY OF HOMING. Carnegie
       Inst. Washington, Dept. Marine Biol. Papers 7: 1-60, illus.

(44) Wetmore, A.

  1923. MIGRATION RECORDS FROM WILD DUCKS AND OTHER BIRDS BANDED IN
       THE SALT LAKE VALLEY, UTAH. U. S. Dept. Agr. Bull. 1145, 16
       pp., illus.

(45) ------------

  1926. THE MIGRATIONS OF BIRDS. 217 pp., illus. Cambridge, Mass.

(46) Winkenwerder, H. A.

  1902. THE MIGRATION OF BIRDS WITH SPECIAL REFERENCE TO NOCTURNAL
       FLIGHT. Wis. Nat. Hist. Soc. (n. s.) 2: [177]-263, illus.




=INDEX=


  Acanthis linaria, 8.
  Accipiter cooperi, 13.
    velox, 13.
  Aerial obstructions, 57.
  Agelaius phoeniceus, 18.
  Altitudes of travel, 22.
  Anas platyrhynchos, 10.
    rubripes, 16.
  Ancestral home theory, 5, 6.
  Anguilla, 24.
  Anoüs stolidus, 24.
  An thus spinoletta rubescens, 55.
  Antrostomus carolinensis, 44.
  Archilochus colubris, 59.
  Arctic route, 52.
  Arctonetta, 52.
  Aristotle, 2, 3.
  Arquatella maritima, 34.
  Astur atricapillus, 8.
  Atlantic coast route, 42.
  Atlantic oceanic route, 39.

  Baeolophus bicolor, 62.
  Baldpate, 47.
  Banding studies, 61.
  Bartramia longicauda, 11.
  Blackbird, 26, 27, 45.
    Brewer's, 26.
    European, 3.
    red-winged, 18, 26, 28, 30.
    rusty, 52.
    yellow-headed, 26.
  Bluebird, 6, 27, 30, 60.
  Bluethroat, 15.
  Bobolink, 26, 44, 53, 54
  Bobwhite, 27, 62, 63.
  Bombycilla garrula, 8.
    garrula pallidiceps, 56.
  Bonasa umbellus, 62.
  Brant, 42.
  Branta bernicola, 42.
    canadensis, 11.
    canadensis minima, 48.
  Bubo virginianus, 27.
  Bullbat, 26.
  Bunting, snow, 27.
  Buteo borealis, 12.
    lagopus, 13.
    platypterus, 13.
    regalis, 13.
    swainsoni, 13.

  Calcarius lapponicus, 30, 57.
  Calidris canutus, 34.
  Canvasback, 42.
  Capella delicata, 30.
  Cardinal, 27, 62.
  Carpodacus mexicanus frontalis, 62.
    purpureus, 56.
  Casmerodius albus egretta, 55.
  Cathartes aura, 27.
  Causes of migration, 5.
  Chaetura pelagica, 4.
  Chamaea fasciata, 62.
  Chen caerulescens, 18.
    hyperborea, 26.
    rossi, 49.
  Chickadee, 5, 55.
    black-capped, 63.
    Carolina, 63.
  Chordeiles minor, 6.
    minor minor, 52.
  Chuck-will's-widow, 44.
  Clarke, W. E., 3.
  Coccyzus americanus, 44.
    erythropthalmus, 44.
  Colaptes auratus, 52.
  Colinus virginianus, 62.
  Compsothlypidae, 26.
  Corvus brachyrhynchos, 18.
  Coturnix coturnix, 2.
  Coues, Elliott, 3.
  Cowbird, 24.
  Crane, 2, 3, 4, 12, 22, 23.
  Creeper, brown, 57.
  Crocethia alba, 23.
  Crossbill, 5, 26.
  Crow, 15, 18, 26.
    Clark's, 55.
  Cuckoo, black-billed, 44.
    yellow-billed, 44.
  Cyanocitta cristata, 27.
  Cyanosylvia suecica, 15.

  Dafila acuta, 18.
  Dendroica aestiva, 11.
    aestiva aestiva, 52.
    caerulescens, 10.
    coronata, 52.
    palmarum, 29.
    palmarum hypochrysea, 29.
    palmarum palmarum, 29.
    pinus, 29.
    striata, 13.
    tigrina, 30.
  Distances, 27.
  Diurnal migration, 11.
  Diving bird, 12.
  Dolichonyx orvzivorus, 44.
  Dove, 3.
    mourning, 15.
    turtle, 2.
  Duck, 2, 11, 12, 15, 26, 27, 30, 34, 43, 45, 47, 52.
    black, 16, 27, 42, 46.
    eider, 52.
    scaup, 42.
    sea, 48.

  Eel, 24.
  Egret, 55.
  Egretta thula thula, 55.
  Euphagus carolinus, 52.
  Exhaustion, 59.

  Falco peregrinus, 15.
  Falcon, peregrine, 15.
  Finch, 34.
    house, 62.
    purple, 56.
    rosy, 55.
  Fishes, 24.
  Flicker, 52.
  Flight speed, 13.
  Florida caerulea caerulea, 55.
  Flycatcher, 11, 12, 15, 25.
  Fregata minor, 25.

  Gätke, Heinrich, 14.
  Geothlypis trichas, 28.
  Goose, 2, 3, 11, 12, 15, 17, 27, 43, 45, 46, 47.
    blue, 18, 26, 46, 47.
    cackling, 48.
    Canada, 11, 17, 18, 26, 42, 43, 60.
    emperor, 52.
    Ross's, 49.
    snow, 26.
  Goshawk, 8.
  Grackle, 30.
    bronzed, 26.
  Great Lakes route, 45.
  Grebe, 27.
  Grosbeak, 37, 56.
    black-headed, 29.
    evening, 56.
    pine, 55.
    rose-breasted, 26, 37.
  Groups, movements of, 8.
  Grouse, ruffed, 62.
  Gull, 12, 13, 52, 56, 59.
    herring, 56.
    Ross's, 52.

  Hawk, 2, 12, 15, 22, 27, 34.
    broad-winged, 13.
    Cooper's, 13.
    duck, 15.
    red-tailed, 12.
    rough-legged, 13.
    sharp-shinned, 13.
    Swainson's, 12, 13.
  Hedymeles ludovicianus, 26.
    melanocephalus, 29.
  Helmitheros vermivorus, 46.
  Herodotus, 2.
  Heron, 15.
    black-crowned night, 55.
    little blue, 55.
    snowy, 55.
  Hesiod, 2.
  Hesperiphona vespertina, 56.
  Hirundinidae, 3.
  Hirundo erythrogaster, 15.
  Historical accounts, 3.
  Homer, 2.
  Hummingbird, ruby-throated, 59.
  Hylocichla minima aliciae, 17.

  Icterus spurius, 6.
  Insects, 24.

  Jacksnipe, 30.
  Jaeger, parasitic, 52.
  Jay, 62.
    blue, 27, 28, 62.
  Junco, 7, 27, 55.
    common, 7.
    slate-colored, 30, 52, 57.
  Junco hyemalis, 7.
    hyemalis hyemalis, 52.

  Kingbird, 26, 44.
    common, 34.
  Kingfisher, belted, 27.
  Kinglet, 58.
    golden-crowned, 57.
  Kite, 3.
  Kittiwake, red-legged, 52.
  Knot, 34.

  Lanius ludovicianus, 29.
  Lapwing, 23.
  Lark, horned, 15.
    meadow, 27, 57.
  Larus argentatus smithsonianus, 56.
  Leucosticte, 55.
  Lobipes lobatus, 23.
  Longspur, 27, 57.
    Lapland, 30, 57.
  Loon, 12.
    yellow-billed, 63, 64.
  Lophortyx californica, 62.
  Loxia curvirostra, 5.
    leucoptera, 5.

  Mackenzie Valley route, 45.
  Magnus, Olaus, 3.
  Mallard, 16, 18, 25, 27, 42.
  Man-o'-war bird, 25.
  Mareca americana, 47.
  Martin, purple, 8.
  Megaceryle alcyon, 27.
  Melanitta, 48.
    deglandi, 43.
  Melospiza melodia, 26.
  Migration, advantages of, 4.
    altitudes, 22.
    distances, 27.
    diurnal, 11.
    fall, 29.
    historical accounts, 3.
    long-distance, 30.
    mystery of, 3.
    nocturnal, 11.
    perils, 56.
    problems, 61.
    routes, 33.
    segregation during, 25.
    short, 27.
    species and groups, 8.
    speed, 13.
    theories of causes, 5.
    undetermined, 27.
    vagrant, 55.
    variable, 28.
    vertical, 55.
    weather, 59.
  Mimus polyglottos, 63.
  Mississippi Valley route
  Mniotilta varia, 9.
  Mockingbird, 63.
  Movements of residents
  Murre, 24.
  Myiochanes richardsoni, 55
  Mystery of migration, 3.

  Nannus hiemalis, 27.
  Nighthawk, 6, 12, 26, 30, 44, 45.
    eastern, 52.
  Nocturnal migration, 11.
  Nucifraga columbiana, 55.
  Nutcracker, 55.
  Nuthatch, 5.
    white-breasted, 63.
  Nyctea nyctea, 8.
  Nycticorax nycticorax hoactli, 55.
  Nyroca affinis, 42.
    americana, 42.
    marila, 42.
    valisineria, 42.

  Oidemia, 48.
  Oncorhynchus, 24.
  Oporornis formosus, 46.
  Orientation, 23.
  Oriole, 11.
    orchard, 6.
  Otus asio, 63.
  Ovenbird, 52, 60.
  Owl, great horned, 27.
    screech, 63.
    snowy, 8, 56.

  Pacific coast route, 47.
  Pacific oceanic route, 49.
  Passerculus princeps, 34.
  Passerella iliaca fuliginosa, 28.
    iliaca iliaca, 28.
  Pelican, 3, 12, 22.
  Penthestes atricapillus, 5.
    carolinensis, 63.
  Perils, aerial obstructions, 57.
    exhaustion, 59.
    migration, 56.
    storms, 56.
  Petrochelidon albifrons, 13.
  Pewee, western wood, 55.
  Phalarope, 27.
    northern, 23.
  Philacte canagica, 52.
  Philohela minor, 30.
  Photoperiodism theory, 6.
  Pigeon, homing, 25.
    racing, 24.
  Pinicola, 55.
  Pintail, 18, 47.
  Pipit, 55.
  Piranga erythromelas, 26.
    ludoviciana, 49.
  Plectrophenax nivalis, 27.
  Pliny, 3.
  Plover, 12.
    American golden, 15.
    eastern golden, 50.
    golden, 39, 40, 50, 51, 59.
    Pacific golden, 49, 54.
    upland, 11.
  Pluvialis dominica, 15.
    dominica dominica, 49.
    dominica fulva, 49.
  Pooecetes gramineus, 30.
  Porzana Carolina, 59.
  Problems, migration, 61.
  Progne subis, 8.

  Quail, 2.
    California, 62.
    migratory, 2.
    western, 27.
  Querquedula discors, 42.
  Quiscalus quiscula, 26.

  Rail, 3, 11, 12.
    Carolina, 59.
  Raven, 15.
  Redhead, 42, 47, 65.
  Redpoll, 8.
  Redstart, 11, 38, 52.
  Residents, movements of, 62.
  Rhodostethia rosea, 52.
  Richmondena cardinalis, 27.
  Riparia riparia, 44.
  Rissa brevirostris, 52.
  Robin, 6, 18, 19, 20, 26, 28, 45, 52, 57.
  Routes, 33.
    Arctic, 52.
    Atlantic coast, 42.
    Atlantic oceanic, 39.
    evolution of, 52.
    Great Lakes, 45.
    Mackenzie Valley, 45.
    Mississippi Valley, 45.
    narrow, 34.
    Pacific coast, 47.
    Pacific oceanic, 49.
    wide, 34.
  Rowan, William, 7.

  Salmon, 24.
  Salpinctes obsoletus, 29.
  Sanderling, 23.
  Sandpiper, 12, 23.
    Bartramian, 11.
    purple, 34.
  Sapsucker, Williamson's, 55.
  Scaup, 42.
  Scoter, 48, 49.
    white-winged, 43, 49
  Segregation, 25.
  Seiurus noveboracensis, 52.
  Setophaga ruticilla, 11, 38.
  Shore bird, 6, 11, 26, 27, 31, 34, 39, 40, 45, 46.
  Shoveler, 43.
  Shrike, 15, 27.
    loggerhead, 29.
  Sialia sialis, 6.
  Sitta canadensis, 5.
    carolinensis, 5.
  Snipe, 12.
    Wilson's, 30.
  Snowbird, 7.
  Somateria, 52.
  Sora, 59.
  Sparrow, 11, 25, 26, 27, 45, 57, 58.
    chipping, 30.
    eastern chipping, 52.
    eastern fox, 28.
    field, 29.
    Harris's, 34, 35, 36.
    Ipswich, 34.
    song, 26, 27, 28.
    sooty fox, 28.
    swamp, 57.
    tree, 27, 30, 57.
    vesper, 30.
    white-throated, 57, 63.
  Spatula clypeata, 43.
  Species, movements of, 8.
  Speed, flight, 13.
    migration, 13.
  Sphyrapicus thyroideus, 55.
  Spizella arborea, 27.
    passerina, 30.
    passerina passerina, 52.
    pusilla, 29.
  Starling, 3.
  Stercorarius parasiticus, 52.
  Sterna forsteri, 31.
    fuscata, 24.
    hirundo, 31.
    paradisaea, 31.
  Stork, 2, 3, 4, 23.
  Storms, 56.
  Sturnella, 27.
  Swallow, 2, 3, 4, 6, 12, 13, 22, 26, 27, 46.
    bank, 44.
    barn, 15, 30, 45.
    cliff, 13, 22, 30.
    hibernating, 3.
  Swan, 3.
  Swift, 4, 12, 15, 27.
    chimney, 4, 26.

  Tanager, 45, 49.
    scarlet, 26, 36.
    western, 49.
  Teal, 43.
    blue-winged, 42, 43.
  Telmatodytes palustris, 27.
  Tern, 25.
    arctic, 31, 33, 51, 52.
    common, 31.
    Forster's, 31.
    noddy, 24.
    sooty, 24.
  Theories of migration, 5.
  Thrush, 3, 11, 15, 25, 30, 45, 58.
    American hermit, 15.
    gray-cheeked, 17, 44.
    hermit, 57.
    wood, 45.
  Thryothorus ludovicianus, 27.
  Titlark, 55.
  Titmouse, 27.
    tufted, 62.
  Turdus migratorius, 6.
    migratorius achrusterus, 28.
    migraiorius migratorius, 28.
  Turtle, 4.
  Tyrannus tyrannus, 34.

  Vagrant migration, 55.
  Vanellus vanellus, 23.
  Vermivora chrysoptera, 46.
  Vertical migration, 55.
  Vireo, 11, 44, 57, 58.
    red-eyed, 52.
  Vireo olivaceus, 52.
  Vulture, 22.
    turkey, 27.

  Warbler, 11, 13, 27, 45, 57, 58.
    black-and-white, 9.
    blackpoll, 13, 20, 45, 52.
    black-throated blue, 10.
    Cape May, 30.
    eastern yellow, 52.
    golden-winged, 46.
    Kentucky, 46.
    myrtle, 45, 52.
    palm, 29.
    pine, 29.
    summer, 17.
    wood, 25, 26.
    worm-eating, 46.
    yellow, 11, 17.
  Waterfowl, 42.
  Waxwing, 26, 27.
    Bohemian, 8, 56.
  Weather, influence of, 59.
  Woodcock, 30.
  Woodpecker, 27.
  Wren, 12.
    Carolina, 27, 62, 63.
    long-billed marsh, 27.
    rock, 29.
    winter, 27, 57.
  Wren-tit, 62.

  Xanthocephalus xanthocephalus, 26.

  Yellowthroat, Maryland, 28.

  Zonotrichia albicollis, 63.
    querula, 34.


U. S. GOVERNMENT PRINTING OFFICE: 1935



       *       *       *       *       *


Transcriber Note

Illustrations moved to prevent splitting paragraphs. Minor typos
corrected. Hyphenation was standardized to the most prevalent used
except those in the Bibliography which were left as printed. The
Index entry _Seiurus noveboracensis_ (Northern Waterthrush) points to
page 52 where the _Seiurus aurocapilla_ (Ovenbird) is described. The
species name in the Index is likely a typo and has been changed.