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                      Phylogeny of the Waxwings
                           and Allied Birds


                                  BY

                            M. DALE ARVEY



                  University of Kansas Publications
                      Museum of Natural History


     Volume 3, No. 3, pp. 473-530, 49 figures in text, 13 tables
                           October 10, 1951


                         UNIVERSITY OF KANSAS
                               LAWRENCE
                                 1951




     UNIVERSITY OF KANSAS PUBLICATIONS, MUSEUM OF NATURAL HISTORY

        Editors: E. Raymond Hall, Chairman, Edward H. Taylor,
                  A. Byron Leonard, Robert W. Wilson

     Volume 3, No. 3, pp. 473-530, 49 figures in text, 13 tables
                      Published October 10, 1951


                         University of Kansas
                           Lawrence, Kansas


                              PRINTED BY
                   FERD VOILAND, JR., STATE PRINTER
                            TOPEKA, KANSAS
                                 1950
                     [Illustration: union label]
                               23-1019




                      Phylogeny of the Waxwings
                           and Allied Birds

                                  by
                            M. DALE ARVEY




CONTENTS


                                                                  PAGE
 Introduction                                                      476
 Acknowledgments                                                   476
 Nomenclatural History                                             477
 Materials                                                         478
 Diagnoses                                                         478
 Coloration                                                        485
 Courtship                                                         489
 Nest Building                                                     491
 Food                                                              493
 Skeleton                                                          494
   Skull                                                           494
   Humerus                                                         499
   Pygostyle                                                       502
   Sternum                                                         505
   Relative Lengths of Bones                                       505
     Leg-trunk Percentages                                         509
     Arm-trunk Percentages                                         511
 Musculature                                                       514
   Caudal Muscles                                                  514
   Pectoral Muscles                                                517
   Hind Limb Musculature                                           517
 Digestive Tract                                                   517
 Origin of the Species                                             519
 Conclusions                                                       521
 Summary                                                           524
 Bibliography                                                      525




INTRODUCTION


A small family of passerine birds, the Bombycillidae, has been
selected for analysis in the present paper. By comparative study of
coloration, nesting, food habits, skeleton and soft parts, an attempt
is made to determine which of the differences and similarities between
species are the result of habits within relatively recent geological
time, and which differences are the result of inheritance from ancient
ancestral stocks, which were in the distant past morphologically
different. On the basis of this information, an attempt is made to
ascertain the natural relationships of these birds. Previous workers
have assigned waxwings alone to the family Bombycillidae, and a
question to be determined in the present study is whether or not
additional kinds of birds should be included in the family.

It has generally been assumed that the nomadic waxwings originated
under boreal conditions, in their present breeding range, and that
they did not undergo much adaptive radiation but remained genetically
homogeneous. Also it is assumed that the species were wide ranging and
thus did not become isolated geographically to the extent that, say,
the Fringillidae did. The assumption that waxwings originated in the
northern part of North America or Eurasia may be correct, but it is
more probable that the origin was more southerly, perhaps, in northern
Mexico, of North America (see p. 519.) Subsequent to the
differentiation of this stock in the south, there was a northerly
movement, while certain populations remained behind and underwent an
evolution different from the northern group. Since the fossil record
does not permit us to say when in geological time the family
originated, we must rely on anatomical evidence and the distributional
evidence of present-day species to estimate when the family stock had
diverged from some unknown group sufficiently to merit the status of a
separate family.




ACKNOWLEDGMENTS


It is with pleasure that I acknowledge the guidance received in this
study from Professor E. Raymond Hall of the University of Kansas. I am
indebted also to Dr. Herbert Friedmann of the United States National
Museum for the loan of certain skins, skeletons, and alcoholic
material; to Mr. Alexander Skutch, for notes on certain Central
American birds; and to Dr. Henry W. Setzer, Mr. George H. Lowery, Jr.,
Mr. Victor E. Jones, Mr. Victor Housholder, Mr. Alvaro Wille-Trejos,
and Mr. Morton F. Davis, for gifts of specimens that have been used in
this work. Suggestions and critical comments from Professors Worthie
H. Horr, Charles G. Sibley and Edward H. Taylor are gratefully
acknowledged. I wish also to thank Mrs. Virginia Unruh for the
preparation of the drawings used in this work.




NOMENCLATURAL HISTORY


The oldest name available for any species of the waxwings is _Lanius
garrulus_ Linnaeus (1758). _Lanius garrulus_ and _Lanius garrulus_
variety B _carolinensis_ were described as conspecific. The
description has been associated with the first of the two names. The
latter name is a _nomen nudum_ since it was not accompanied by a
separate description. The generic name _Lanius_ was originally applied
to both shrikes and waxwings by Linnaeus. Since that name is applied
to the shrikes only, the next available generic name that may be
applied to the generically different waxwings must be used. This is
_Bombycilla_, a name originally proposed by Brisson (1760) for the
Cedar Waxwing. In the 12th Edition of the Systemae Naturae (1766)
Gmelin proposed the generic name _Ampelis_ for the Bohemian Waxwing,
and combined it with the specific name _garrulus_, the Cedar Waxwing
being termed variety B. Vieillot (1807) proposed the generic name
_Bombycilla_ and combined it with a new specific name, _cedrorum_, for
the Cedar Waxwing. Vieillot has been cited as the author of
_Bombycilla_ since that time, although Brisson used _Bombycilla_ 33
years before. Oberholser (1917) did not cite Brisson's work in his
discussion of the proper generic name for the waxwings, and
_Bombycilla_ should be ascribed to Brisson and not Vieillot, since
Opinion 37, rendered by the International Zoölogical Committee on
Nomenclature, states that generic names used by Brisson (1760) are
valid under the Code. In consequence, the specific name available for
the Cedar Waxwing, since Brisson is ruled not to be a binomialist, is
_Bombycilla cedrorum_ Vieillot (1807).

Most workers prior to 1900 utilized the family name Ampelidae to
include waxwings, silky flycatchers, and palm-chats. Ridgway
(1904:113) elevated the silky flycatchers to family rank under the
name Ptilogonatidae, and assigned the palm-chats to a separate family,
the Dulidae.




MATERIALS


The following specimens, numbering 238, and representing each
currently recognized species and subspecies, were used in the study,
and were supplemented by observation in 1947 on specimens in the
United States National Museum.


  ====================================================================
          Species or Subspecies           | Skin | Skeleton| Alcoholic
  ----------------------------------------+------+---------+----------
  _Phainoptila melanoxantha melanoxantha_ |    8 |    1    |    2
  _Phainoptila melanoxantha minor_        |    2 |         |
  _Ptilogonys cinereus cinereus_          |   13 |    3    |    4
  _Ptilogonys cinereus molybdophanes_     |    6 |         |
  _Ptilogonys caudatus_                   |   16 |    3    |    4
  _Phainopepla nitens nitens_             |      |    1    |    5
  _Phainopepla nitens lepida_             |   12 |    5    |    4
  _Bombycilla cedrorum_                   |   53 |   27    |    8
  _Bombycilla garrula garrula_            |    4 |    3    |
  _Bombycilla garrula centralasiae_       |    9 |    2    |
  _Bombycilla garrula pallidiceps_        |    7 |    3    |    2
  _Bombycilla japonica_                   |   10 |         |
  _Dulus dominicus dominicus_             |    9 |    5    |    2
  _Dulus dominicus oviedo_                |    4 |    1    |
                                          |---------------------------
      Totals                              |  153 |   54    |   31
  --------------------------------------------------------------------




DIAGNOSES


Family Bombycillidae

_Diagnosis._--Bill short, flat, somewhat obtuse, minutely notched near
tip of each maxilla, flared at base; gape wide and deeply cleft;
culmen convex; nasal fossa broad, exposed, or filled with short, erect
or antrorse, close-set velvety feathers; nostril narrowly elliptical;
rictal vibrissae long, short, or absent; lacrimal bone free,
articulating at two points; wings long and pointed, or short and
rounded; primaries ten, tenth reduced in some species; tail short,
narrow, even, two thirds or less length of wing, or much longer and
forked or rounded; feet weak (except in _Dulus_ and _Phainoptila_);
tarsus generally shorter than middle toe and claw, distinctly
scutellate with five or six divisions, the lateral plate subdivided
(except in _Phainoptila_); lateral toes of nearly equal length; hallux
approximately as long as inner lateral toe, or shorter; basal phalanx
of middle toe more or less united to that of outer and inner toes;
body stout; head generally conspicuously crested; plumage soft, smooth
and silky (except in _Dulus_); eggs spotted; nest in trees; three
subfamilies, five genera, eight species.


Subfamily Ptilogonatinae

_Diagnosis._--Rictus with conspicuous bristles; nasal fossa almost
entirely exposed; tail long and rounded, graduated, or square; caudal
muscles and pygostyle well developed; wings rounded and short, first
primary a half to a third as long as second; second primary shorter
than third; humerus long, with small external condyle; plumage soft
and silky, less so in _Phainoptila_; sexes dissimilar, young like
adult female; three genera, four species.


Genus =Phainoptila= Salvin

  _Phainoptila_ Salvin, Proc. Zoöl. Soc. London, 1877:367, April 17,
    1877. Type _Phainoptila melanoxantha_ Salvin.

_Diagnosis._--Without crest; tarsus longer than middle toe and claw,
and booted or very slightly reticulate; tail shorter than wing,
rounded; nostril exposed, ovate; rictal bristles distinct; first
primary well developed; plumage normal, bill flared slightly at base.

_Range._--Costa Rica and Panamá.


=Phainoptila melanoxantha melanoxantha= Salvin

Phainoptila

  _Phainoptila melanoxantha melanoxantha_ Salvin, Proc. Zoöl. Soc.
    London, 1877:367; April 17, 1877.

_Diagnosis._--Coloration of adult males: Pileum, hindneck, back,
scapulars, and upper tail coverts Black (capitalized color terms after
Ridgway, Color Standards and Color Nomenclature, Washington, D. C.,
1912), with Bluish Gray-Green gloss; rump Lemon Yellow tinged with
Olive; lower breast and abdomen Gull Gray or Slate Gray; sides and
flanks clear Lemon Yellow; lower chest, upper breast, and under tail
coverts Yellowish Olive-Green, extending to patch on sides and flanks
of same color; bill and feet Black or Blackish Brown. Coloration of
adult females: Most of upper parts Olive-Green, with Yellowish Olive
on rump; thighs Olive-Gray, as are sides of head; rest of coloration
as in male. Coloration of young: As in adult female, but duller
throughout.

_Measurements._--Wing 99.0, tail 88.5, culmen 15.2, tarsus 28.4.

_Range._--Highlands of Costa Rica and extreme western Panamá (Volcán
de Chiriquí).


=Phainoptila melanoxantha minor= Griscom

Phainoptila

  _Phainoptila melanoxantha minor_ Griscom, Amer. Mus. Novitates,
    141:7, 1924.

_Diagnosis._--Coloration as in _P. m. melanoxantha_, but female with
hindneck more extensively gray and of slightly darker shade; rump,
upper tail coverts, and edgings to tail feathers slightly greener,
less yellow; average size smaller than in _P. m. melanoxantha_.

_Range._--Highlands of westeran Panamá (Cerro Flores and eastern
Chiriquí).


Genus =Ptilogonys= Swainson

  _Ptilogonys_ Swainson, Cat. Bullock's Mex. Mus., App. 4, 1824.
    Type _Ptilogonys cinereus_ Swainson.

_Diagnosis._--Tail much longer than wing, even or graduated; head with
bushy crest; nostril large, rounded and fully exposed, bordered by
membrane; rictal bristles well developed; tarsus shorter than middle
toe with claw; plumage soft, blended.

_Range._--Southwestern United States to Costa Rica.


=Ptilogonys cinereus cinereus= Swainson

Ashy Ptilogonys

  _Ptilogonys cinereus cinereus_ Swainson, Cat. Bullock's Mex. Mus.,
    App. 4, 1824.

_Diagnosis._--Coloration of adult male: Frontals, supralorals, malars,
and chin White; orbital ring White; auriculars and nape grayish brown;
rest of head smoke gray; back, scapulars, wing coverts, rump, and
upper tail coverts plain Bluish Black; rectrices (except middle pair)
with large patch of White midway between base and tip, rest plain
Bluish Black; chest, breast, and anterior parts of sides plain Bluish
Gray-Green, much lighter than back, and fading into paler Gray on
throat; abdomen and thighs White; flanks and posterior part of sides
Olive-Yellow or Yellowish Olive; under tail coverts Lemon Yellow;
bill, legs and feet Black. Coloration of adult females: Head plain
Smoke Gray, passing into White on frontals, malars, and chin; back,
scapulars, wing coverts, and rump Hair Brown; upper tail coverts Dark
Gull Gray; remiges and rectrices Black with faint Dusky Green gloss,
edged with Gull Gray; chest Dark Grayish Brown lightening to Wood
Brown on sides and flanks; abdomen White; under tail coverts Yellow
Ocher. Coloration of young: As in adult female, but paler throughout.

_Measurements._--In adult male, wing 94.0, and tail 104.2; in adult
female, wing 93.3, and tail 94.8; both sexes, culmen 11.1, and tarsus
18.7.

_Range._--Mountainous districts of central and southern Mexico, in
states of Durango, Zacatecas, Hidalgo, México, Oaxaca, Colima,
Morelos, Veracruz, San Luís Potosi, Guerrero and Michoacán.


=Ptilogonys cinereus molybdophanes= Ridgway

Ashy Ptilogonys

  _Ptilogonys cinereus molybdophanes_ Ridgway, Man. N. American Birds,
    464 (footnote), 1887.

_Diagnosis._--Coloration of adult male: Upper parts darker bluish than
in _P. c. cinereus_; venter paler; flanks Olive-Green rather than
Olive as in _P. c. cinereus_. Coloration of adult female: Like female
of _P. c. cinereus_ but colors darker throughout; dorsum more
olivaceous.

_Measurements._--In adult male, wing 89.4, and tail 97.1; in adult
female, wing 89.4, and tail 93.3; both sexes, culmen 11.7, and tarsus
17.3.

_Range._--Western Guatemala, in subtropical and temperate zones.


=Ptilogonys caudatus= Cabanis

Costa Rican Ptilogonys

  _Ptilogonys caudatus_ Cabanis, Jour. für Orn., 1866:402, Nov. 1866.

_Diagnosis._--Coloration of adult male: Forehead and crown Pale
Grayish Blue, slightly paler anteriorly; orbital ring Lemon Yellow;
rest of head and neck, including crest, Olive-Yellow; throat paler and
tinged with Light Gull Gray; back, scapulars, rump, upper tail coverts
and wing coverts uniform Bluish Slate-Black; chest and breast similar
but paler; sides and flanks Yellowish Olive-Green; thighs, lower
abdomen, and under tail coverts Lemon Yellow; remiges, primary coverts,
and tail Black, glossed with Bluish Black and edged with Gull Gray;
inner webs of rectrices (except two middle pair) with large middle
patch of White; bill, legs, and feet Black. Coloration of adult
female: Forehead and crown Pale Gull Gray, becoming paler anteriorly;
rest of head, together with neck, back, scapulars, rump, and wing
coverts plain Yellowish Olive Green; chest and breast similar but more
grayish; lower abdomen and flanks White tinged with Yellowish Olive;
under tail coverts Olive-Gray; remiges, primary coverts, and rectrices
Black with Gull Gray edges. Coloration of young: Dorsum plain Light
Grayish Olive; upper tail coverts Brownish Olive; underparts Grayish
Olive anteriorly, becoming more Yellowish Olive on abdomen; under tail
coverts pale Yellowish Olive with Grayish Olive base; bill and feet
Brownish Drab.

_Measurements_--In adult male, wing 96.2, and tail 135.7; in adult
female, wing 93.9, and tail 113.7; both sexes, culmen 12.6, and tarsus
19.1.

_Range._--Highlands of Costa Rica and extreme western Panamá.


Genus =Phainopepla= Sclater

  _Phainopepla_ Sclater, Proc. Zoöl. Soc. London, 26:543, 1858. Type
    _Phainopepla nitens_ (Swainson).

_Diagnosis._--Tail almost as long as wing; head with pointed crest of
narrow, separated feathers; rectrices without white; bill narrow,
compressed terminally; conspicuous white patch under wing; nostril
small, exposed; rictal bristles distinct; tail slightly rounded.


=Phainopepla nitens nitens= (Swainson)

Phainopepla

  _Phainopepla nitens nitens_ (Swainson), Anim. in Menag., 1838:285,
    Dec. 31, 1837.

_Diagnosis._--Coloration of adult male: Uniform glossy Bluish Black;
inner webs of primaries except innermost pair with middle portion
White; bill, legs, and feet Black. Coloration of adult female: Plain
Olivaceous Black, longer feathers of crest Black, edged with Gull
Gray; remiges and rectrices Dusky Drab to Black; rectrices and coverts
margined by White; bill and feet Brownish Drab to Dusky Brown.
Coloration of young: Like adult female but more Brownish Drab.

_Measurements._--No specimens examined; larger than _P. n. lepida_
(Van Tyne, 1925).

_Range._--Central and southern Mexico, in states of Coahuila, San Luís
Potosi, Durango, Guanajuato, México, Puebla, and Veracruz.


=Phainopepla nitens lepida= Van Tyne

Phainopepla

  _Phainopepla nitens lepida_ Van Tyne, Occ. Pap. Bost. Soc. Nat.
    Hist., 5:149, 1925.

_Diagnosis._--Coloration same as _P. n. nitens_; separated by smaller
size.

_Measurements._--Wing 91.0, tail 90.3, culmen 11.5, tarsus 17.6.

_Range._--Southwestern United States, from central California,
southern Utah, and central western Texas southward to Cape San Lucas
in Baja California, and into northwestern Mexico (Sonora and
Chihuahua).


Subfamily =Bombycillinae=

_Diagnosis._--Wings long and pointed, reaching almost to tip of tail;
first primary spurious; second primary longest; tail short and even;
rictal vibrissae few and short; secondaries generally, and sometimes
also rectrices, tipped with red, corneous appendages; nasal fossa
partly filled with short, antrorse, close-set velvety feathers;
plumage soft, silky; tail tipped with yellow band (red in _B.
japonica_); sexes alike; humerus short with large external condyle;
caudal muscles and pygostyle not well developed; bill flared widely at
base; one genus, three species.

_Range of subfamily._--Holarctic breeding area; wanders nomadically
south in winter to Central America and West Indies, southern Europe
and Asia.


Genus =Bombycilla= Brisson

  _Bombycilla_ Brisson, Orn. ii, 1760:337. Type _Bombycilla garrula_
    (Linnaeus).

_Diagnosis._--As described for the subfamily.


=Bombycilla cedrorum= Vieillot

Cedar Waxwing

  _Bombycilla cedrorum_ Vieillot, Hist. Nat. Amer., 1:88, Sept. 1, 1807

_Diagnosis._--Coloration of adults: Shading from Saccardo's Umber on
dorsum to Bister on top of head; upper tail coverts and proximal
rectrices Gull Gray; underparts shade through pale Lemon Yellow wash
on belly into White on under tail coverts; forehead, lores, and
eye-stripe Black; chin same, soon shading into Blackish Mouse Gray and
into color of breast; side of under jaw with sharp White line; narrow
line bordering forehead, and lores, White; lower eyelid White; quills
of remiges Dark Mouse Gray, darkening at tips; inner quills tipped
with red horny wax appendages; tail feathers like primaries, but
tipped with Lemon Yellow, and occasionally showing also red horny wax
appendages; bill and feet Black. Coloration of young: Dorsum as in
adult, but lightly streaked with White; head concolor with dorsum;
forehead White; lores Black; eye stripe Black anterior to eye and
White posterior to eye; throat Light Buff; belly with alternate
streaks of Dresden Brown and light Ochraceous Buff but posteriorly
White; tail tipped with Lemon Yellow bar; bill black at tip, shading
to Sepia at base.

_Measurements._--Wing 92.9, tail 55.5, culmen 10.9, tarsus 16.8.

_Range._--Breeds from central British Columbia, central Alberta and
Manitoba, northern Ontario, southern Quebec and Cape Breton Island
south to northwestern California, northern New Mexico, Kansas,
northern Arkansas, North Carolina, and northern Georgia. Winters south
to Louisiana, Mississippi, Texas, Arizona, Colorado, Florida,
Honduras, Costa Rica, Jamaica, Little Cayman Island, Haiti, and
Panamá.


=Bombycilla garrula= (Linnaeus)

Bohemian Waxwing

  _Bombycilla garrula_ (Linnaeus), Syst. Nat., 10th Ed., 1758:55.

_Diagnosis._--Coloration of adults: General color Olive-Brown, shading
insensibly from clear Smoke Gray of upper tail coverts and rump to
Cinnamon-Drab anteriorly, heightening on head and forehead to Hazel;
narrow frontal line, lores, broader mask through eye, chin, and upper
throat, Sooty Black; under tail-coverts Cinnamon-Brown; tail Smoke
Gray, deepening to Blackish Mouse Gray distally, and tipped with Lemon
Yellow; wings Blackish Mouse Gray; primaries tipped with sharp spaces
of Lemon Yellow or White, or both; secondaries with White spaces at
ends of outer web, shafts usually ending with enlarged, horny red
appendages; primary coverts tipped with White; bill Blackish Slate and
paler at base; feet Black. Coloration of young: Much like adult, but
general color duller; some streaking on venter and back; chin, throat,
and malar region dull White. Three subspecies.


=Bombycilla garrula garrula= (Linnaeus)

Bohemian Waxwing

  _Bombycilla garrula garrula_ (Linnaeus), Syst. Nat., 10th Ed.,
    1758:55.

_Diagnosis._--Coloration: As described for the species, but darkest of
the three subspecies; tending to be more Vinaceous dorsally than
either _pallidiceps_ or _centralasiae_.

_Measurements._--Wing 113.5, tail 63.1, culmen 12.5, tarsus 20.7.

_Range._--Europe; breeds north to northern Russia and Norway, south to
about 65° N latitude; winters south to England and Ireland, southern
France, northern Italy, and Turkey.


=Bombycilla garrula centralasiae= Poljakov

Bohemian Waxwing

  _Bombycilla garrula centralasiae_ Poljakov, Mess. Orn. vi:137, 1915.

_Diagnosis._--Coloration: As described for the subspecies _garrula_,
but less Vinaceous dorsally, and more Cinnamon; venter lighter gray
than _garrula_, and much paler than _pallidiceps_.

_Measurements._--Wing 114.7, tail 63.0, culmen 12.2, tarsus 21.0.

_Range._--Asia; breeds northern Siberia south to Vladivostok; winters
to Turkestan and central eastern China and Japan.


=Bombycilla garrula pallidiceps= Reichenow

Bohemian Waxwing

  _Bombycilla garrula pallidiceps_ Reichenow, Orn. Monats. 16:191, 1908.

_Diagnosis._--Coloration: As described for the species, but more
grayish above and below than _B. g. garrula_; darker gray than in
_centralasiae_.

_Measurements._--Wing 115.1, tail 71.7, culmen 12.6, tarsus 21.1.

_Range._--Breeds from western Alaska to northern Mackenzie and
northwestern Manitoba south to southern British Columbia, southern
Alberta, northern Idaho, and possibly Colorado (Bergtold 1924) and
Montana (Burleigh 1929); winters east to Nova Scotia and irregularly
over much of Canada, and south irregularly to Pennsylvania, Ohio,
Michigan, Indiana, Kansas, Colorado, California, Arizona, and Texas.


=Bombycilla japonica= (Siebold)

Japanese Waxwing

  _Bombycilla japonica_ (Siebold), Nat. Hist. Jap., St. No. 2:87, 1824.

_Diagnosis._--Coloration: Dorsum generally Brownish Drab shading to
Light Brownish Drab on lower back, rump, and upper tail coverts;
secondary and tertiary coverts Pale Brownish Drab, washed on outer web
with Carmine; primary coverts Blackish Slate, with White edging; tail
feathers Slate-Gray, broadly tipped with Carmine, bordered anteriorly
by subterminal Black bar; head crested, forehead Chestnut; lores,
frontals, and stripe extending around eye and nape, Black; throat
Black, narrowing on lower throat; breast, sides of flanks Light Drab;
venter pale Sulphur Yellow; thighs Brownish Drab; under tail coverts
Carmine; bill, legs, and feet Black.

_Measurements._--Wing 108.3, tail 53.6, culmen 11.2, tarsus 19.4.

_Range._--Breeds eastern Siberia, northern China; winters south in
China, and to Japan (Hokkaido, Kyushu), Taiwan, and Korea.


Subfamily _Dulinae_

_Diagnosis._--Bill deep and compressed, culmen strongly depressed;
nostrils circular, wholly exposed; tail even, and shorter than wing;
tenth primary less than half length of ninth; under parts streaked;
plumage hard and harsh; rictal bristles minute; wing rounded; humerus
long and with small external condyle; pygostyle and caudal muscles not
well developed; one genus, one species.

_Range of subfamily._--Islands of Haiti and Gonave, Greater Antilles.


Genus _Dulus_ Vieillot

  _Dulus_ Vieillot, Analyse, 1816:42.

_Diagnosis._--Like the subfamily.


=Dulus dominicus dominicus= (Linnaeus)

Palm-chat

  _Dulus dominicus dominicus_ (Linnaeus), Syst. Nat., 12th Ed.,
    1766:316.

_Diagnosis._--Coloration: Dorsum Olive, back, scapulars, and wing
coverts more Brownish Olive; lower rump and upper tail coverts
Olive-Green; pileum and hindneck with indistinct streaks of Brownish
Olive; tail Brownish Drab, edged with Light Olive Gray; lores,
suborbital region, and auricular regions Dusky Brown; malars Dusky
Brown and streaked with Sooty Black, streaks narrower on abdomen,
broader and paler on under tail coverts, bill Light Brownish Drab;
legs and feet Brownish Drab.

_Measurements._--Wing 85.0, tail 68.8, culmen 15.0, tarsus 24.7.

_Range._--Island of Haiti, Greater Antilles.


=Dulus dominicus oviedo= Wetmore

Palm-chat

  _Dulus dominicus oviedo_ Wetmore, Proc. Biol. Soc. Wash., 42:117,
    1929.

_Diagnosis._--Coloration: Like _D. d. dominicus_, but averaging more
Grayish Olive; rump and tail coverts with less greenish wash.

_Measurements._--Wing 90.1, tail 71.3, culmen 16.2, tarsus 25.1.

_Range._--Gonave Island, off Haiti, Greater Antilles.




COLORATION


The general coloration of waxwings is cryptic, that is to say,
concealing or blending. The lighter color of the venter, especially of
the belly, contrasts with the duller, darker vinaceous color of the
dorsum. Several ruptive marks tend to obliterate the outline of the
body. The crest of the head, when elevated, tends to elongate the
body, making the outline less like that of a normal bird. The facial
mask effectively breaks up the outline of the head, and conceals the
bright eye, which would otherwise be strikingly distinct. The white
spots on the distal ends of the secondaries of _B. garrula_ and the
yellow color on the distal ends of the rectrices (red in _B.
japonica_) are also ruptive. These ruptive marks on an otherwise
blending type of plumage might be important to waxwings, and probably
are more effective when the birds remain motionless in either a
well-lighted area or in one that is partly in shadow, rather than in
one that is wholly in shadow.

The red wax tips on the secondaries of the flight feathers, and
sometimes found on the ends of the rectrices in _Bombycilla_, are
puzzling and no wholly convincing reason has been suggested for their
occurrence. Two instances are known of yellow instead of red-colored
wax tips in _B. cedrorum_ (Farley, 1924). It is well known that many
individuals, especially of _B. cedrorum_, do not possess these tips;
they are absent in a smaller proportion of individuals of _B.
garrula_. Of the 53 skins of _B. cedrorum_ available in the University
of Kansas Museum of Natural History, which might be taken as a
sampling at random of the general population of this species, only 17
possess wax tips. A few specimens are unilateral, and the tips are of
varying sizes in different individuals. Of these 17 birds, 6 are
female and 7 male, the others being unsexed at the time of skinning.
This proportion is, roughly, half and half. Of the seven skins of _B.
garrula pallidiceps_ in the same Museum, five possess the tips, and
two that are females have no trace of the red tips at all. Of the five
which do have the tips, two are males, two are females, and one is
unsexed. In a series of 13 specimens of the three subspecies of _B.
garrula_, loaned by the United States National Museum, all but two
individuals possess the tips on the secondaries, and, in addition,
four specimens, equally divided between the two sexes, have color on
the rachis of some rectrices, and small appendages of pigment extend
beyond the feathers. Stevenson (1882) found that among 144 specimens
of _B. garrula garrula_ killed by storms in England in the winter of
1866-67, 69 individuals had wax tips. Of these, 41 were males and 27
were females; the remaining one was of uncertain sex. Among 38
definitely sexed _B. garrula pallidiceps_ in the California Museum of
Vertebrate Zoölogy, Swarth (1922:276) lists tips in 22 males and 16
females. These data indicate that the proportion of birds with the wax
tips is higher in _B. garrula_ than in _B. cedrorum_. The potentiality
for wax tips is possibly inherited according to Mendelian ratio.

_Bombycilla japonica_ is of interest in that the adults, at least,
seldom have the waxy appendages. Nevertheless, in the specimens
observed, the entire distal ends of the feathers normally possessing
the tips in other species are suffused with red color. This may be the
original condition of all waxwings, or perhaps, instead, this species
is in a transitional stage in the development of the tips. Swarth
(1922:277) says concerning the probable derivation of the wax tips in
_B. garrula_ (and in _B. cedrorum_): "the ornamentation, in fact, may
well have begun with the coloring of the shaft, spreading later over
adjoining feather barbs. The last stage would have been the coalescing
of the barbs, forming the waxlike scale as is now seen. Various steps
of this hypothetical development are supplied in the wing and tail
feathers of different birds of this series." _Bombycilla japonica_
thus may be close to the ancestral condition in the waxwing stock in
the development of the waxy appendage.

The rectrices of all three species of waxwings seldom possess the wax
tips, unless the secondaries have the maximum number of tips. In these
individuals, the pigment seems to "spill over" onto the tail feathers.
Eight is the maximum number of tips found on the secondaries.
Rectrices with wax tips are more frequently found in _B. garrula_, and
only occasionally in _B. cedrorum_. The pigment in the tip of the tail
of _B. japonica_ is red rather than yellow as it is in the other two
species, and some individuals of the Japanese Waxwing show a slight
amount of coalescence of wax in the tail feathers as well as in the
secondaries.

If the tips were present in all members of the two species, it could
be postulated, in line with recent investigational work by Tinbergen
(1947), that the tips are in the nature of species "releasers,"
facilitating species recognition. Such recognition is now regarded as
of prime importance in the formation of species. It is improbable that
sex recognition may be aided, as there is no evidence to indicate that
the tips are found predominantly in either sex.

The wax tips are not limited to the adult birds in the species _B.
garrula_. Swarth (_op. cit._) mentions the capture of several young
Bohemian Waxwings, and describes them as "possessing all the
distinctive markings of the most highly developed adult." This
includes wax appendages, and several citations are given (Wolley 1857,
Gould 1862) to indicate that this is the rule rather than the
exception, not only for the American subspecies _pallidiceps_, but at
least for the European subspecies _garrula_ as well. On the other
hand, the young of _B. cedrorum_ lack the wax tips, at least as far as
available data show.

Some characteristics of living animals are of the "relict" type; that
is to say, they were developed in ancient times when some unknown
ecological factor was operative which is no longer demonstrable, and
the characteristic is now neutral or at least not detrimental,
although of no positive value to the organism. Possibly the wax tips
of waxwings are thus to be explained. I am more inclined to the
opinion that the wax tips are adaptations to present-day ecological
conditions for the birds.

The wax tips are ruptive in effect, since the birds, especially in
winter, are habitués of bushes and trees that have berries, and the
tips, on the otherwise dull body, suggest berries. The red tips tend
further to disrupt the body outline at the midline, or slightly
posterior to this. Perhaps the wax tips on the rectrices emphasize the
end of the tail, the region of the body that is the least vital and
that may be expendable in times of pursuit by an enemy.

Any characteristic is of survival value to an organism if in any way
the characteristic enhances the chances of survival up to the time
when the organism can successfully raise even a few young to maturity.
If that character, as for example, the red wax tips on the
secondaries, helps to maintain the individual until it can raise to
independence a greater number than merely a few young, such a
character can be said to be of greater survival value. The character
may be effective for a brief period of time and may be uncommon; it
might be effective for a split second in time, and only at a
particular stage in the life history.

The winter period probably is the most hazardous for waxwings, in that
they then depend at times upon long flights to find food. The food is
vegetable, and thus is comparatively low in food value; the birds must
ingest large quantities of berries or dried fruits to maintain
themselves. In winter, in northern latitudes at least, predators are
more apt to prey upon those species which, like waxwings, do not
migrate south. The winter months are those in which waxwings frequent
berry bushes, and it may well be that in these months, the wax tips
that appear like berries, are especially valuable to the birds, and
operate selectively.

It is suggested, therefore, that the wax tips are of positive value to
waxwings, rather than being relict characters. Coalescence of pigment
has taken place in the formation of the wax tips. _B. japonica_ is
closer to the ancestral stock insofar as wax tips are concerned, and
generally lacks the tips. _B. cedrorum_ has the tips in approximately
half of the adults, and not at all in the young. _B. garrula_ has the
tips in almost all the adults, and in a like proportion of the young,
and probably has evolved further in the development and retention of
the wax tips than has either of the other two species.

The streaked plumage of _Dulus_ is decidedly generalized, and is
probably more nearly like the color of the ancestral stock. In this
connection it is notable that young Cedar Waxwings are streaked, and
young Bohemian Waxwings are streaked to a lesser degree. This
streaking is apparently a recapitulation of the feather color of the
stock. Perhaps the color of _Dulus_ has not changed, as the streaking
would not be a disadvantage to the birds in their environment of light
and shadow. In joining together in groups and in the construction of
large communal nests, _Dulus_ has evidently gained sufficient
protection against predators; other birds solve this problem by
modifying their coloration.

_Ptilogonys_ is ruptively colored, but in a different fashion than
_Bombycilla_. The tail markings, the distinct yellow on the under tail
coverts, the sharply marked pileum, are all examples of ruptive
coloration. The generally lighter venter (especially under tail
coverts), the crest that may be elevated, and the generally drab
bluish dorsum, are cryptic and serve to hide the animal insofar as is
possible considering its habits. The very conspicuous coloration of
the male, in contrast to the more drab color of the female, however,
would lead one to believe that in _Ptilogonys_, following the pattern
of many passerine birds, the male leads a predator from the nest,
leaving the drab female to incubate the eggs, and thus preserve the
young.

It is difficult to suggest reasons for the brilliant coloration of the
male _Phainopepla_, unless it is for decoying predators away from the
nest. Possibly some birds survive not because of, but in spite of,
their coloration, and _Phainopepla_ may be a case of this sort. Anyone
who has observed _Phainopepla_ in life will agree, certainly, that the
male makes no attempt at concealment, and flaunts his color to all
comers.

The coloration of _Phainoptila_, in contrast to _Phainopepla_, is much
more plain, and is suited to its habits of brush dwelling; in a brush
habitat the drab coloration is difficult to detect. The Yellowish
Olive under tail-coverts and the Olivaceous dorsum are all evidences
of cryptic coloration, and undoubtedly, this bird depends upon hiding
for escape from its enemies, since it is a bird of the dense forest
cover.

Coloration, which varies relatively rapidly in response to differing
ecological conditions, has become more different in the species of
Bombycillidae than is true in many other families of passerine birds.
The explanation lies in early geographical isolation of the three
subfamilies, with consequent radiation in three directions. Waxwings
have become adapted by possessing a thick protective layer of feathers
and drab coloration broken by ruptive marks. They still retain the
streaked plumage, which is probably ancestral, in the juveniles; this
is lost at the first molt in the fall. In its evolution, _Dulus_ has
developed large feet, heavy decurved beak, and the large communal nest
that affords protection from enemies; as a consequence, perhaps
_Dulus_ did not need a plumage different from the primitive and
streaked one. The survival of _Dulus_ may not have depended on either
ruptive marks or on brilliant and outstanding plumage. The large feet
and large bill seem to be responses to particular ecological
requirements, as will be shown later.

The Ptilogonatinae, with habits paralleling those of the flycatchers,
probably are considerably modified from the ancestral stock; the
coloration probably is more brilliant and conspicuous. Perhaps this
type of coloration and the habit of capturing insects from a perch are
correlated. Some amount of territoriality is characteristic of this
subfamily and dimorphism in color--the plumage of the male is
outstandingly conspicuous--possibly is of selective value to the race.
In a tropical forest community, a duller pattern possibly would be
more visible and thus would be selectively disadvantageous.




COURTSHIP


Waxwings are gregarious birds and individuals establish no
well-defined territories as do many birds. The nest itself is the only
defended territory, and as Crouch (1936) has shown, the Cedar Waxwing
will nest in close proximity to others of the same species. Swarth
(1932:275) mentions that the Bohemian Waxwing is tolerant of the nests
of other pairs near by. The extreme condition is that found in
_Dulus_, in which the territory is not limited even to the nest, but
to the individual compartment of the community nest. _Phainopepla_, a
less gregarious bird than _Dulus_ and waxwings, has a much more
definite territory, although individuals of _Phainopepla_ are tolerant
of others of the same species; no feeding territory is established,
and small flocks of birds feed together at any time of the year.

In birds whose territories lack well-defined boundaries, it would be
expected that elaborate song would not have evolved, and that most of
the recognition of kind and sex would be dependent upon the behavior
of the birds. This is the fact; song, as such, is lacking in the three
subfamilies Bombycillinae, Ptilogonatinae, and Dulinae. Waxwings utter
(1) notes that serve to keep the flock together, (2) calls used by the
young in begging for food, and (3) some low notes that Crouch (_op.
cit._:2) considered as possibly concerned with courtship.
_Phainopepla_ has various call notes, and in addition, a succession of
notes which are run together. _Ptilogonys_ utters a note which Skutch
(MS) characterizes as a loud, not unmusical "tu-whip" that is used as
the birds "fly in straggling parties which keep in contact by their
constant chatter." _Dulus_ is described by Wetmore and Swales
(1931:349) as having only a variety of rather harsh chattering notes
in chorus.

The most notable behavior pattern associated with courtship in
Waxwings, in the absence of song, is the so-called "mating dance"
described by Crouch (1936), and observed by me in Lawrence, Kansas, in
the spring of 1948. This consists of one bird of a pair (presumably
the male) hopping along a branch toward the other bird (the female),
then away again, repeating the procedure for some little time. The
female remains motionless until, as the male approaches, mutual
fondling of the head and neck feathers takes place, or the birds may
peck at each other's bill. A berry may be passed from bill to bill,
although generally the berry is not utilized for food, and this can be
interpreted as a nervous reaction of the birds. It may be an instance
of "false feeding" as is seen in many birds, in which the female begs
for food, as a nestling would beg, as a preliminary to the sexual act.
I am of the opinion that these reactions are in the nature of
behavioristic patterns that bring the birds into the emotional balance
for copulation, as copulation follows the "dance." Sometimes, however,
copulation is preceded by a "nuptial flight" around the nesting area,
at which time the birds utter loud calls. Armstrong (1924:183) is of
the same opinion, citing numerous instances in which nuptial flights
and elaborate displays have evolved for just this purpose. The birds
are then in the proper physiological balance to initiate the
complicated sequence of copulation, nesting, incubation, feeding, and
brooding of the young.

It would be valuable to know more concerning the life histories of the
other birds considered in this paper, since behavior is inherent, and
probably can be cited as evidence of close relationship or the
opposite. All that I have been able to learn is that _Phainopepla_ has
a nuptial flight in which the male chases the female, and that _Dulus_
(Wetmore and Swales, 1931:347) seeks the company of others of its kind
at all times, and that two birds, presumably paired, will sidle up to
one another when they are perched.




NEST BUILDING


There are numerous papers concerning the nesting of waxwings. _B.
garrula_, owing to its nesting in the far north, where observers are
few, has received less attention than _B. cedrorum_. There is, on the
other hand, no literature that deals with the nesting habits of the
majority of the Ptilogonatines, with the exception of _Phainopepla_,
on which there is considerable literature (Merriam, 1896; Myers, 1907,
1908). No detailed study of the nesting of _Dulus_ has been reported,
although Wetmore and Swales (1931) have described carefully the large
communal nest of this genus.

In _Bombycilla_, both members of a pair apparently aid in the
construction of the nest (Crouch, 1936; Swarth, 1932). Although the
sexes are alike in plumage and general appearance, most students of
the nesting of waxwings agree that one bird, assumed to be the female,
does most of the arranging of the material, and does the shaping of
the nest, whereas both birds carry materials to the nest site. As is
characteristic of many passerine birds, both members of the pair
gather materials and fly back to the nest site, where the female takes
the more active part in the construction of the nest itself.

Both species of American waxwings build bulky nests, with the base or
platform composed of a large amount of twigs and sticks, from which
there often trails a mass of sticks and moss or string. Softer
materials such as moss, plant fibers, and string, are placed inside
the platform; moss is readily available to, and preferred by, _B.
garrula_ according to Swarth (_op. cit._:271), and various plant
fibers and string are used by _B. cedrorum_. The inner lining consists
of soft plant fibers or down, dry grasses, and feathers. The nest is
usually unconcealed in a tree either adjacent to a trunk or on a main
side branch, but sometimes in a fork. Nest building by both Cedar and
Bohemian waxwings is rapid, taking from three to five days, and is
followed immediately by egg laying.

Nesting by waxwings is late in the season; June is the month in which
the nest is usually started. This is readily explainable in Bohemian
Waxwings, since adverse weather would prohibit earlier nesting in the
area in which they spend the summer. Crouch (_op. cit._:1) remarks
that _B. cedrorum_ possibly evolved in the far north where it was
impossible for it to start nesting earlier, and that the habit has
been retained. Perhaps, on the other hand, nesting is delayed until
the berry crop is ripe, to insure sufficient food for the young.

Desertion of the nest is not uncommon in waxwings, despite the
tolerance to other animals that is shown by the birds. A new nest may
suddenly be begun before the first one is finished, and all the
materials from the first nest may be removed, or the nest may be
abandoned before it is completed. The eggs may be left at any time up
to hatching, and the young may be deserted, especially in the earlier
stages of development.

The very large and bulky communal nest of _Dulus_ is not radically
different from the nest of waxwings. In the absence of sufficient
nesting sites, a pair of gregarious birds such as _Dulus_ could
combine their nest with those of other pairs, retaining for their own
territory only the nest cavity, and in this way communal nests might
have evolved. The nest of _Dulus_ is communal probably because of the
lack of suitable trees for nesting sites, and only incidentally does
this type of nest afford better protection from natural marauders.
Large numbers of Palm-chats work together in the construction of the
nest platform, and both sexes probably take part in the work.

In _Phainopepla_ the nest is built mostly by the male (Merriam, 1896;
Myers, 1908), although the female does some of the work, especially in
the shaping and lining of the nest. In this genus, the nest is usually
a compact structure, but exceptional nests are of considerable bulk.
The nest is commonly placed in a fork near the main trunk of a tree,
in a conspicuous location, and generally is 10 to 20 feet from the
ground. In shape and location, the nest closely corresponds to that of
_Bombycilla_, but the materials used for a base are stems of annual
plants, whereas _Bombycilla_ uses more woody twigs. The finer
materials used by _Phainopepla_ are more readily obtainable in the
ecological association inhabited by _Phainopepla_ than would be
heavier twigs such as _Bombycilla_ uses.




FOOD


Waxwings are typically frugivorous; berries are the staple food. The
birds are known to catch insects, especially in the spring and summer,
and their insect gathering technique has been likened to that of
Tyrannid flycatchers. Nice (1941) experimented with a young captive
Cedar Waxwing and found that it had a decided preference for red or
blue berries, and that meal worms were utilized as food only when the
birds became educated by other captive birds of other species as to
the food value of the worms. Post (1916) indicates that the food given
to the nestlings of Cedar Waxwings is entirely animal for the first
three days, and that a mixed diet of berries and insects is
subsequently offered.

In feeding of the young, regurgitation of partly digested food does
not take place, according to Wheelock (1905). Rather, the adults
"store" food in the form of berries in the expanded esophagus or crop,
feeding them whole to the young. Digestion is an unusually rapid
process, involving merely minutes for the passage of berries and
cherries. This is correlated with a short intestinal tract, which is
unusual for a frugivorous bird. Nice's (1940) experiments with Cedar
Waxwings revealed that cherries would pass through the digestive tract
in 20 minutes, blueberries in 28 minutes, and chokecherries in 40
minutes. Heinroth (1924) states that berries pass through the
digestive tract of Bohemian Waxwings in the space of a "few minutes."
This rapid digestion is obviously adaptive, since the value of the
food is slight and therefore large quantities of it must be ingested;
the large seeds would hamper further ingestion until they were
eliminated, since they seem not to be regurgitated.

Members of the subfamily Ptilogonatinae are both insectivorous and
frugivorous insofar as available data show, although again there is
relatively little information available concerning them. Skutch (MS)
has found that the Guatemalan _Ptilogonys cinereus_ catches insects by
repeated sallies into the air from a perch, after the manner of
flycatchers. He notes also that the birds feed on berries of _Eurya
theoides_ and _Monnina xalapensis_. It is well known that
_Phainopepla_ catches insects when these are available, and its liking
for berries is so apparent that in parts of its range, it is known as
the "pepper bird," since it frequents pepper trees (_Schinus molle_)
and feeds on the small red berries. The preserved specimens of
_Ptilogonys_ and _Phainoptila_ available for this study contain only
berries in the digestive tract. _Dulus_ feeds mostly, if not wholly,
on plant food. According to Wetmore and Swales (1931:349), berries,
fruits, and parts of flowers are eaten.




SKELETON


A critical analysis of the skeletons provides evidence that aids the
student in estimating which differences are merely the result of
habits developed in relatively recent geological time as opposed to
those which owe their existence to more ancient heritage. Stresses
caused by the action of different sets of muscles can apparently
stimulate changes in bones to meet new needs, and the evidence from
genetics is that such mutations in wild birds are minute and
cumulative, rather than of large degree and of sudden appearance. Once
adaptive mutations have occurred, if genetic isolation from one source
or another accompanies it, a new population different from the
parental stock may become established. Study of the skeleton of any
species of living bird may indicate those characters identifiable as
modifications fitting it to a particular environment. If no
distinguishing characters are discovered that may be attributed to
environmental factors, such a species can be spoken of as generalized;
the inference then is that such a species is not modified for a
single, particular ecological niche.

Some parts of the skeleton, obviously, are more adaptable or plastic
than others. The beak seems to be the most adaptable part. Probably
this results from its frequent use; it is the part of the bird to
capture the food. The long bones, meeting the environment as legs
which serve as landing mechanisms or as locomotory appendages, and as
wings which provide considerable locomotion for most birds, probably
come next in order as regards plasticity. In these parts, then, one
may look for the most change in birds, which, within relatively recent
geologic times, have been modified to fit a particular set of
conditions. From the beak and long bones of a species in which habits
are unknown, one can infer the habits and habitat from a comparison
with the skeletal features of species of known habits.


_Skull._--The skulls in all three subfamilies have essentially the
same general appearance and structure, the most marked differences
being, as would be expected, in the bills and associated bones.

The most specialized bill is to be found in _Dulus_; its bill is
decurved, and the associated bones are correspondingly changed for
support of the bill. For example, the palatines and "vomer" are much
wider, the palatines are more concave from below and have longer
posterior processes than the corresponding bones in _Bombycilla_.
Moreover, the "vomer" in _Dulus_ and in _Phainoptila_ is larger and
heavier than in _Bombycilla_, and the quadrate and pterygoid bones are
relatively large for support of the beak. The palatines, however, are
weak in _Phainoptila_. In the Ptilogonatinae, with the exception of
_Phainoptila_, the wings of the palatines flare more than in
_Bombycilla_, but not to the extent that they do in _Dulus_, nor does
the palatine bone present a concave appearance in the Ptilogonatinae.
The premaxilla is a relatively weak bone in _Bombycilla_ and
_Phainopepla_, stronger in _Ptilogonys_, and is notably heavy in
_Phainoptila_ and _Dulus_, and in these latter two genera shows a
sharply-ridged tomium. The maxillae connect to somewhat widened nasal
and naso-lateral processes in all the genera, and the premaxillae
narrow abruptly from this point forward. In the family, _Phainopepla_
and _Phainoptila_ show the least flaring in this region.


  [Illustration: Figs. 1-7. Skulls in lateral view of five genera of
                 Bombycillidae. Natural size.

     1. _Phainoptila m. melanoxantha_, sex?, MNH no. 26493, 15 mi.
        SE Cartago, Costa Rica.

     2. _Ptilogonys caudatus_, male, MNH no. 24492, 15 mi. SE Cartago,
        Costa Rica.

     3. _Phainopepla nitens_, male, MNH no. 24752, Pima Co., Arizona.

     4. _Ptilogonys cinereus_, female, Louisiana State University
        no. 297, Xilitla Region, San Luís Potosi, Mexico.

     5. _Dulus dominicus_, female, USNM no. 292652, Don Don, Haiti.

     6. _Bombycilla cedrorum_, male, MNH no. 15331, Bexar Co., Texas.

     7. _Bombycilla garrula_, sex?, USNM no. 223895, Bozeman, Montana.]


  [Illustration: Figs. 8-14. Skulls in ventral view of five genera of
                 Bombycillidae. Natural size.

     8. _Phainoptila m. melanoxantha_, sex?, MNH no. 26492, 15 mi.
        SE Cartago, Costa Rica.

     9. _Ptilogonys caudatus_, male, MNH no. 24492, 15 mi. SE Cartago,
        Costa Rica.

    10. _Phainopepla nitens_, male, MNH no. 24754, Pima Co., Arizona.

    11. _Ptilogonys cinereus_, female, Louisiana State University
        no 297, Xilitla Region, San Luís Potosi, Mexico.

    12. _Dulus dominicus_, female, USNM no. 292652, Don Don, Haiti.

    13. _Bombycilla cedrorum_, male, MNH no. 15331, Bexar Co., Texas.

    14. _Bombycilla garrula_, sex?, USNM no. 223895, Bozeman, Montana.]


  [Illustration: Figs. 15-21. Skulls in dorsal view of five genera of
                 Bombycillidae. Natural size.

    15. _Phainoptila m. melanoxantha_, sex?, MNH no. 26493, 15 mi.
        SE Cartago, Costa Rica.

    16. _Ptilogonys caudatus_, male, MNH no. 24492, 15 mi. SE Cartago,
        Costa Rica.

    17. _Phainopepla nitens_, male, MNH no. 24752, Pima Co., Arizona.

    18. _Ptilogonys cinereus_, female, Louisiana State University
        no. 297, Xilitla Region, San Luís Potosi, Mexico.

    19. _Dulus dominions_, female, USNM no. 292642, Don Don, Haiti.

    20. _Bombycilla cedrorum_, male, MNH no. 15331, Bexar Co., Texas.

    21. _Bombycilla garrula_, sex?, USNM no. 223895, Bozeman, Montana.]


This flaring, immediately lateral to the antorbital plate, is common
to all Bombycillids and constitutes a major skeletal characteristic
useful for recognition of the members of the family, since the
swelling is easily discernible both externally and on the cleaned
skulls. In _Phainopepla_ there is much variability in this character;
some specimens have a narrower antorbital bridge than others. Only one
skeleton of _Phainopepla n. nitens_ was available. The flaring in the
skull of this specimen is identical with that in _Ptilogonys_. Among
the skulls of _P. n. lepida_ in the University of Kansas Museum of
Natural History, is No. 19228, a juvenile, taken 5 miles south of
Tucson, Arizona. In this specimen, the flaring in the antorbital
region is clearly evident and equal in amount to that in skulls of _P.
n. nitens_, but the bird had not attained full skeletal growth.
However, the flaring of the antorbital region appears to be common in
the nestlings of many species of passerine birds. Other specimens of
the subspecies _lepida_ show a varying amount of flaring, the least
(in the series available) being in No. 24754, MNH, in which the
proportion of the skull (length divided by width) closely corresponds
to that in _Phainoptila_; the skull of No. 24754 is long and thin, and
the base of the bill is only slightly swollen. The skull of
_Phainopepla nitens lepida_ is more generalized than that of
_Phainopepla n. nitens_, having a longer and narrower bill like the
generalized _Phainoptila_. In _Phainopepla n. nitens_ and in members
of the genus _Ptilogonys_, more flaring occurs in the antorbital
region.

_Phainoptila_, as noted above, has no great amount of flaring in the
antorbital region. When more specimens of _Phainoptila_ are examined,
the base of the bill probably will be found to flare more in some
individuals than in others; this would be expected if we may judge by
the data on _Phainopepla_. The premaxilla and maxilla of _Phainoptila_
are similar to the same bones in _Dulus_, and there is a well-marked
ridge on the tomium (possibly for cutting flower parts). In
_Phainoptila_, the palatines are narrower than in any other genus of
the family and abut the lacrimals. The entire skull appears to be
modified along different lines from those of the skull of _Dulus_; the
skull of _Phainoptila_ seems to be modified for a frugivorous rather
than an insectivorous diet. The skull of _Phainoptila_ probably is
more nearly similar to the ancestral skull than is that of any other
living species in the family. The wide gape characteristic of some
members of the family is undoubtedly a modification for aiding in the
capture of insects, and _Phainoptila_ has progressed less in this
direction than have other species in the family.

The mandibles vary somewhat in the shape and proportionate size of the
bones. The mandible is proportionately, as well as actually, highest
in _Dulus_. The medial condyle varies to some extent, being slightly
flattened mediad in _Bombycilla_, and less so in the other genera. The
mandible of _Bombycilla_ narrows to the symphysis much more gradually
than it does in the other genera.

The antorbital plate is large and divides the orbital chamber from the
nasal chamber. The small lacrimal bone anterior to the plate
articulates with the maxilla and the premaxilla. Shufeldt (1889)
states that the free lacrimal ossicle might be of some taxonomic
importance in the passerines, since it is found in the generalized
Corvids and in nestling Turdids. I find it well developed and
identical, with a double articulation and free ends, in all the
Bombycillids. There is no significant variability in the family, and
this is more evidence of close taxonomic relationship between the
members of the family.

The size of the crania is somewhat variable, although the differences
seem to be primarily those of proportion. Ptilogonatinae have long
crania, whereas the crania of the Bombycillinae and Dulinae are
shorter but deeper. I regard the longer cranium as primitive, and it
is longest in _Phainoptila_. In order of decreasing relative length of
the cranium, _Phainoptila_ is followed by _Ptilogonys caudatus_, _P.
cinereus_, and _Phainopepla_. _Bombycilla garrula_ has the deepest
cranium in the family.

The measurements of the lengths and widths of the skulls are given in
Table 9. The relative length of the bill and relative width of the
skull are given in Table 10. These relative measurements are
calculated by using the actual measurements in Table 9 as numerators,
the length of the skull from the lacrimal bone to the posteriormost
end of the skull being used as the denominator. The data indicate that
_Phainoptila_ has a slightly narrower cranium.


_Humerus._--Certain families of passerine birds have a noticeable
variation in the characteristics of the humerus; the bone varies in
length, in diameter, and in the complexity of the processes at either
end. In the Bombycillids, however, the amount of variation is
relatively small, and the diaphysis of the bone is somewhat twisted,
especially so in _Dulus_. The deltoid tuberosity is variable, being
shorter but more elevated in _Bombycilla_ than it is in the
Ptilogonatinae and in the Dulinae. The tendon from the pectoralis
major muscle, which inserts on this process, probably finds better
insertion on a higher process than on a lower but longer one.


  [Illustration: Figs. 22-28. Humeri of five genera of Bombycillidae.
                 Natural size.

    22. _Phainoptila m. melanoxantha_, sex?, MNH no. 26493, 15 mi.
        SE Cartago, Costa Rica.

    23. _Ptilogonys caudatus_, male, MNH no. 24492, 15 mi. SE Cartago,
        Costa Rica.

    24. _Phainopepla nitens_, male, MNH no. 24754, Pima Co., Arizona.

    25. _Ptilogonys cinereus_, female, Louisiana State University
        no. 297, Xilitla Region, San Luís Potosi, Mexico.

    26. _Dulus dominicus_, female, USNM no. 292652, Don Don, Haiti.

    27. _Bombycilla cedrorum_, male, MNH no. 15331, Bexar Co., Texas.

    28. _Bombycilla garrula_, sex?, USNM no. 223895, Bozeman, Montana.]


Distally, the two major condyles and the intercondylar groove or
olecranon fossa that make efficient articulation with the ulnar
process, are not variable. The external condyle, however, is
significantly variable in the family. This condyle is longest and most
pronounced in birds in which the humerus is short in relation to the
trunk, as for example in _Tachycineta_. In the Bombycillidae the
condyle is smallest in _Phainoptila_, where it is a mere suggestion of
a process. In the remainder of the Ptilogonatinae, the condyle is
larger but rounded, and shows a double process in _Ptilogonys
caudatus_, and a slightly pointed process in _P. cinereus_. The
external condyle in _Dulus_ is not specialized, being low and rounded,
but in _Bombycilla_, it is noticeably elongated, indicating a better
attachment distally for the deltoid muscle. (No measurements are
tabulated for this condyle, as the percentage of error in measuring
this small structure is great.) Table 1 gives lengths of humeri, and
Table 2 gives lengths of the humeri expressed as percentages of the
length of the trunk, a standard measurement.

The area of insertion of the deltoid muscle is elongated in those
birds with shortened humeri; these birds have also greater flight
power than do birds with longer humeri and therefore a shorter
external condyle.


  Table 1. Lengths of Arm Bones in cm.

  =========================+=========+========+======+=======
           Species         | Humerus | Radius | Ulna | Manus
  -------------------------+---------+--------+------+-------
  Ptilogonys caudatus      |   2.39  |  2.57  | 2.79 |  2.25
  Ptilogonys cinereus      |   2.24  |  2.48  | 2.78 |  2.38
  Phainopepla nitens       |   2.21  |  2.59  | 2.82 |  2.39
  Phainoptila melanoxantha |   2.40  |  2.51  | 2.70 |  2.25
  Dulus dominicus          |   2.23  |  2.38  | 2.63 |  2.31
  Bombycilla garrula       |   2.35  |  2.58  | 2.88 |  2.67
  Bombycilla cedrorum      |   2.06  |  2.34  | 2.60 |  2.38
  -------------------------+---------+--------+------+-------


  Table 2. Arm-trunk Ratios (in percent)

  =========================+=========+========+======+=======+=======
           Species         | Humerus | Radius | Ulna | Manus | Total
  -------------------------+---------+--------+------+-------+-------
  Ptilogonys caudatus      |    85   |   92   |  93  |   80  |  2.58
  Ptilogonys cinereus      |    84   |   90   | 103  |   89  |  2.76
  Phainopepla nitens       |    84   |   98   | 107  |   91  |  2.82
  Phainoptila melanoxantha |    73   |   77   |  82  |   69  |  2.31
  Dulus dominicus          |    78   |   83   |  92  |   81  |  2.51
  Bombycilla garrula       |    69   |   75   |  87  |   78  |  2.34
  Bombycilla cedrorum      |    67   |   76   |  85  |   77  |  2.29
  -------------------------+---------+--------+------+-------+-------


  Table 3. Arm-trunk Ratios (in percent)

  =========================+=========+========+======+=======+=======
           Species         | Humerus | Radius | Ulna | Manus | Total
  -------------------------+---------+--------+------+-------+-------
  Corvus brachyrynchos     |    90   |  101   | 111  |  106  |  307
  Dendroica audubonii      |    68   |   82   |  90  |   77  |  237
  Setophaga ruticilla      |    69   |   82   |  91  |   75  |  235
  Myadestes townsendi      |    71   |   84   |  96  |   81  |  248
  Sialia sialis            |    72   |   84   |  98  |   86  |  256
  Hylocichla mustelina     |    75   |   81   |  92  |   80  |  247
  Parus atricapillus       |    85   |   90   | 106  |   81  |  272
  Tachycineta thalassina   |    71   |   95   | 107  |  128  |  306
  Myiarchus crinitus       |    83   |  105   | 115  |   92  |  290
  Dumetella carolinensis   |    76   |   75   |  89  |   78  |  243
  Polioptila caerulea      |    85   |   93   | 105  |   71  |  261
  Eremophila alpestris     |    91   |   99   | 110  |   95  |  296
  Muscivora forficata      |    85   |  111   | 120  |  108  |  313
  -------------------------+---------+--------+------+-------+-------


_Pygostyle._--This part of the skeletal system is variable in the
species dealt with, not so much in size as in complexity. It reflects,
of course, the character of the caudal muscles and their size, as well
as the length of the rectrices and the corresponding force necessary
to hold these feathers upright and in a useful position. Firm
attachment is important even in flight, because the tail is used as a
rudder, and in the Ptilogonatinae as a brake. The pygostyle is most
modified in this subfamily.

In lateral aspect, the pygostyles of the species of the Ptilogonatinae
are similar. The crest of the bone is flattened dorsally, and has a
broad anterior surface that is thin and bladelike. This is widest in
_Ptilogonys caudatus_, and narrowest in _Phainoptila_, in which genus,
however, the entire bone is of small size. The centrum is widest in
_Ptilogonys caudatus_, and is progressively narrower in _P. cinereus_,
_Phainopepla_, and _Phainoptila_. Greater width provides a larger area
of attachment for the larger rectrices and also more area for
insertion of the lateralis caudae muscle, the size of which varies
more than that of the other caudal muscles in the different species of
the Bombycillidae.


  [Illustration: Figs. 29-35. Pygostyles in posterior view of five
                 genera of Bombycillidae. × 2.

    29. _Phainoptila m. melanoxantha_, sex?, MNH no. 26493, 15 mi.
        SE Cartago, Costa Rica.

    30. _Ptilogonys caudatus_, male, MNH no. 24492, 15 mi. SE Cartago,
        Costa Rica.

    31. _Phainopepla nitens_, male, MNH no. 24754, Pima Co., Arizona.

    32. _Ptilogonys cinereus_, female, Louisiana State University
        no. 297, Xilitla Region, San Luís Potosi, Mexico.

    33. _Dulus dominicus_, female, USNM no. 292652, Don Don, Haiti.

    34. _Bombycilla cedrorum_, male, MNH no. 15331, Bexar Co., Texas.

    35. _Bombycilla garrula_, sex?, USNM no. 223895, Bozeman, Montana.]


In proportionate size (see Table 7), the pygostyle of _Bombycilla_ is
the smallest in the family. The dorsal spinous portion is acutely
pointed instead of flattened as in the Ptilogonatinae. In _Dulus_, the
spinous portion is extremely thin, and shows a decided curve dorsad
from the centrum, and there is no flattened area anterior to the
spinous portion as is seen in _Ptilogonys_.

The centrum in cross section varies considerably. In _Bombycilla_ the
walls are indented, with definite terminal knobs; both knobs and
indentations are more pronounced in _B. garrula_ than in _cedrorum_,
however. The spinous portion is enlarged in both species, and the rest
of the neck region is constricted (Figs. 29-35).

The centrum of _Dulus_ in posterior aspect presents the appearance of
a simple shield; little of the indentation seen in _Bombycilla_ is
present. The spinous portion is plain, with no constriction nor
terminal enlargement in the neck. The centrum in _Phainopepla_ is
similar to that in _Dulus_, but has a small expansion at the base of
the spine, the entire centrum being wider in proportion to its
over-all size than in any of the other species mentioned previously.
The centrum in _Ptilogonys_ shows great width, and the spine is in a
large expanded tip as in _Bombycilla_. The lateral edges of the
centrum in _P. cinereus_ are "winged" and in two separate halves;
whereas the centrum of _P. caudatus_ is fairly plain, its
specialization being reflected primarily in breadth and flatness. In
cross section of the centrum, _Phainoptila_ is similar to
_Phainopepla_, although, in the former, the bone is smaller in
proportion to the size of the animal, and the lateral wings are more
angular than in _Phainopepla_.


  [Illustration: Figs. 36-42. Pygostyles in lateral view of five
                 genera of Bombycillidae. × 2.

    36. _Phainoptila m. melanoxantha_, sex?, MNH no. 26493, 15 mi.
        SE Cartago, Costa Rica.

    37. _Ptilogonys caudatus_, male, MNH no. 24492, 15 mi. SE Cartago,
        Costa Rica.

    38. _Phainoptila nitens_, male, MNH no. 24754, Pima Co., Arizona.

    39. _Ptilogonys cinereus_, female, Louisiana State University
        no. 297, Xilitla Region, San Luís Potosi, Mexico.

    40. _Dulus dominicus_, female, USNM no. 292652, Don Don, Haiti.

    41. _Bombycilla cedrorum_, male, MNH no. 15331, Bexar Co., Texas.

    42. _Bombycilla garrula_, sex?, USNM no. 223895, Bozeman, Montana.]


In specialization for muscle attachment, the centra of the pygostyles
of the Ptilogonatinae have more area for muscle attachment than do the
centra in the Bombycillinae and Dulinae; the centrum is wide, the
spinous portion is long, and the bone is flattened anteriorly. The
most generalized pygostyle is in _Phainoptila_, and that of _Dulus_
differs only slightly. In _Bombycilla_ the pygostyle is
proportionately small, but is complex in shape; there is seemingly not
the need for greatly expanded areas since the caudal muscles are less
specialized in this genus.


_Sternum._--The sternum in Bombycillids is typically passerine in
general shape and in having a long and deep carina or sternal crest.
The caudal process of the bone is broad, with the terminal ends
flattened, forming dorsally a graceful V-shaped outline, whereas the
outline of the posterior end of the sternum is broad and convex.

In lateral aspect, the carina is deeper in _Bombycilla_ than in other
genera of the family, and is deepest in _B. garrula_. In this species,
the manubrium is more extended and comparatively larger than in the
other species of the family. The anterior edge of the keel forms the
sharpest angle in _B. cedrorum_. In _Dulus_, the keel is moderately
deep, the manubrium short, and there is a distinct indented curve
between the manubrium and the anterior angle of the keel.

In ventral aspect the lateral processes of the sternum tend to flare
outwards in adult Ptilogonatines on almost the same plane as the rest
of the bone, whereas in _Bombycilla_ and _Dulus_ the same process is
closer to the body of the sternum. In _Bombycilla_ the xiphoid process
is more dorsal in position than in other species in the family, and in
_Dulus_ an upward curve is very noticeable. The process in these two
genera is narrower than in the Ptilogonatinae, and lacks the heavy
distal terminal enlargement which is apparent in _Ptilogonys_.


_Relative Lengths of Bones._--In instances where the animals being
compared are obviously different in over-all size, it is useful to
express the size of a given part in relation to some other part of the
same individual organism if the aim is to obtain clues as to
differences in functions of the parts being compared. Differences in
actual lengths of corresponding bones in two kinds of animals often,
of course, reflect only the difference in over-all size of the
animals. Consequently, the relative size of the part is expressed as a
percentage in this paper. In computing a percentage it is well, of
course, to select some relatively stable part of the animal to use as
a denominator in the mathematical expression that yields the
percentage. The thoracic region of the vertebral column is thought to
be such a part. For example, the length of the humerus divided by the
length of the thoracic region yields, in _Phainopepla_ and
_Ptilogonys_, respective percentages of .84 and .85. These are roughly
the same, whereas the actual lengths of the humeri are 2.21 and 2.39
cm.


  Table 4. Lengths of Leg Bones in cm.

  =========================+=======+=============+=================
           Species         | Femur | Tibiotarsus | Tarsometatarsus
  -------------------------+-------+-------------+-----------------
  Ptilogonys caudatus      |  2.04 |     3.10    |       1.94
  Ptilogonys cinereus      |  1.89 |     2.90    |       1.77
  Phainopepla nitens       |  1.76 |     2.78    |       1.72
  Phainoptila melanoxantha |  2.43 |     3.77    |       2.58
  Dulus dominicus          |  2.09 |     3.34    |       2.09
  Bombycilla garrula       |  2.32 |     3.46    |       1.99
  Bombycilla cedrorum      |  1.92 |     2.95    |       1.64
  -------------------------+-------+-------------+-----------------


  Table 5. Leg-trunk Ratios (in percent)

  ====================+=======+=============+=================+=======
           Species    | Femur | Tibiotarsus | Tarsometatarsus | Total
  --------------------+-------+-------------+-----------------+-------
  Ptilogonys caudatus |   73  |     110     |        69       |  252
  Ptilogonys cinereus |   71  |     109     |        66       |  246
  Phainopepla nitens  |   69  |     106     |        65       |  240
  Phainoptila         |   74  |     115     |        60       |  249
       melanoxantha   |       |             |                 |
  Dulus dominicus     |   73  |     119     |        73       |  265
  Bombycilla garrula  |   68  |     101     |        59       |  228
  Bombycilla cedrorum |   63  |      96     |        53       |  212
  --------------------+-------+-------------+-----------------+-------


  Table 6. Leg-trunk Ratios (in percent)

  =======================+=======+=============+=================+======
          Species        | Femur | Tibiotarsus | Tarsometatarsus | Total
  -----------------------+-------+-------------+-----------------+------
  Corvus brachyrynchos   |   71  |     120     |       77        |  268
  Corvus corax           |   73  |     139     |       78        |  290
  Dendroica audubonii    |   62  |     109     |       81        |  252
  Setophaga ruticilla    |   66  |     127     |       94        |  287
  Myadestes townsendi    |   61  |      99     |       60        |  220
  Sialia sialis          |   66  |     111     |       72        |  249
  Hylocichla mustelina   |   75  |     133     |       97        |  305
  Parus atricapillus     |   78  |     138     |       99        |  315
  Tachycineta thalassina |   61  |      97     |       56        |  214
  Myiarchus crinitus     |   68  |     106     |       74        |  248
  Dumetella carolinensis |   73  |     136     |       94        |  303
  Polioptila caerulea    |   75  |     144     |      113        |  332
  Eremophila alpestris   |   73  |     113     |      115        |  301
  Muscivora forficata    |   62  |      98     |       61        |  221
  -----------------------+-------+-------------+-----------------+------


  Table 7. Actual Length and Width in mm. of Pygostyle and Proportionate
  Length and Width of Pygostyle in percent of Lacrimal Length

  =========================+========+=======+=========+=========
                           |        |       | Length, | Width,
           Species         | Length | Width | percent | percent
  -------------------------+--------+-------+---------+---------
  Ptilogonys caudatus      |   9.8  |  3.9  |    45   |    18
  Ptilogonys cinereus      |   8.8  |  4.1  |    41   |    19
  Phainopepla nitens       |   8.4  |  3.9  |    41   |    19
  Phainoptila melanoxantha |   8.5  |  3.5  |    35   |    14
  Dulus dominicus          |   8.5  |  2.9  |    38   |    13
  Bombycilla garrula       |   7.0  |  3.5  |    31   |    15
  Bombycilla cedrorum      |   7.1  |  2.9  |    35   |    14
  -------------------------+--------+-------+---------+---------


  Table 8. Length of Sternum and Depth of Carina expressed as
  percentages of the Length of the Trunk

  =========================+=========+========
           Species         | Sternum | Carina
  -------------------------+---------+--------
  Ptilogonys caudatus      |    85   |   28
  Ptilogonys cinereus      |    91   |   32
  Phainopepla nitens       |    81   |   26
  Phainoptila melanoxantha |    76   |   25
  Dulus dominicus          |   107   |   28
  Bombycilla garrula       |    88   |   33
  Bombycilla cedrorum      |    82   |   31
  -------------------------+---------+--------


  Table 9. Skull and Sternum, Length and Width in mm.

  =========================+========+=======+=========+=========
                           | Length | Width | Length  |  Width
           Species         |   of   |  of   |   of    |   of
                           | Skull  | Skull | Sternum | Sternum
  -------------------------+--------+-------+---------+---------
  Ptilogonys caudatus      |  34.9  |  15.6 |   23.9  |   7.8
  Ptilogonys cinereus      |  33.4  |  14.7 |   24.3  |   8.5
  Phainopepla nitens       |  33.3  |  15.1 |   21.3  |   6.9
  Phainoptila melanoxantha |  39.7  |  16.0 |   24.8  |   8.2
  Dulus dominicus          |  36.4  |  16.6 |   30.5  |   8.0
  Bombycilla garrula       |  37.0  |  16.8 |   30.0  |  11.2
  Bombycilla cedrorum      |  34.0  |  15.5 |   25.3  |   9.6
  -------------------------+--------+-------+---------+---------


The length of the trunk was taken as the distance from the anterior
tip of the neural crest of the last cervical vertebra to the anterior
edge of an acetabulum. The number of free thoracic vertebra was five
in each specimen; consequently, there was no error from this source.
In the cranium, a measurement was taken from the anterior edge of the
lacrimal bone to the posteriormost end of the cranium, and the
resultant figure was employed for a constant in cases in which small
bones were compared.


  Table 10. Relative Length and Width of Skull (in percent)

  =========================+========+=======
                           | Length | Width
           Species         |   of   |  of
                           | Skull  | Skull
  -------------------------+--------+-------
  Ptilogonys caudatus      |   160  |   72
  Ptilogonys cinereus      |   158  |   69
  Phainopepla nitens       |   162  |   73
  Phainoptila melanoxantha |   161  |   65
  Dulus dominicus          |   164  |   75
  Bombycilla garrula       |   164  |   74
  Bombycilla cedrorum      |   162  |   74
  -------------------------+--------+-------


  [Illustration: Fig. 43. Part of skeleton of _Bombycilla cedrorum_
                 showing method of measuring the length of the trunk.
                 Natural size.]


_Leg-trunk Percentages._--Table 4 shows the relative lengths of the
legs and of the separate bones in the legs of the different species of
the Bombycillids. Table 5 shows corresponding lengths for other
passerine birds. The total length of the leg was computed by adding
the figures obtained for the lengths of the femur, tibiotarsus and
tarsometatarsus. The lengths of the toes were disregarded. Length of
leg was recorded in this same way by Richardson (1942:333), who
thought that only in swimming and running birds do the toes contribute
to the functional length of the hind limb.

Table 4 shows that of the birds compared in this paper, _Dulus_ has
the longest legs. In order of decreasing length the others are the
Ptilogonatinae, and finally the Bombycillinae, which have the shortest
legs of all. In Waxwings the length of the legs, expressed as
percentages of the body-lengths, are identical with those birds that
are similar in habits, that is to say, birds which do not use the hind
limb except in perching. It can be noted by reference to Table 5 that
_Tachycineta_ and _Myadestes_ fall into this category. This shortness
of limb is obviously adaptive, and each of the segments of the limb
has been correspondingly shortened, with no element reduced at the
expense of the other two. The short leg can be more easily folded
against the body while the bird is in flight, than can a long leg
which is more unwieldy. It may be noted from tables 4 and 5 that birds
which spend much time on the ground, or that hop a great deal in the
underbrush, have longer legs than do birds which spend much time in
flight. Two birds with noticeably long legs are _Hylocichla
mustelina_, a typical ground dweller, and _Parus atricapillus_, which
hops about in the trees and underbrush.

Insofar as the lengths of the legs show, _Dulus_ and _Phainoptila_ are
the most generalized of the Bombycillidae, since the relative length
of leg is approximately the same as that of more generalized birds
such as warblers, crows and thrushes of similar locomotory habits. In
other words, _Dulus_ and _Phainoptila_ have remained unspecialized, in
contrast to the waxwings in which adaptive changes fitting them for a
perching habit have taken place. _Ptilogonys_ and _Phainopepla_ are
intermediate in length of leg between _Phainoptila_ and _Bombycilla_,
and _Ptilogonys_ and _Phainopepla_ have progressed from life on the
ground toward the perching habit. _Bombycilla cedrorum_ is more
specialized than is _B. garrula_ in shortness of leg, and the
reduction is comparable, as is noted above, to that in the legs of
_Tachycineta_.

In birds which have the legs much modified for walking or for hopping
in the brush, such as _Polioptila_ and _Eremophila_, it is noteworthy
that the distal segment, the tarsometatarsus, is the longest, whereas
in birds such as _Myiarchus_ and _Tachycineta_, that do not utilize
the limbs in this manner, the tibiotarsus, the middle segment, is the
longest. Mammals much modified for walking or hopping likewise have
the proximal segment, the femur, short, and the distal segment long
(Howell, 1944). The waxwings have all of the segments short; these
birds are modified for strong and sustained flight. Their hind limbs
are used principally for landing devices and for perching. No one
element of the leg has been shortened much, if any, more than any
other.


  [Illustration: Fig. 44. Graph showing relative lengths of bones of
                 the leg. The percentage values are shown on the axis
                 of the ordinates.

    A. _Bombycilla cedrorum_; B. _Bombycilla garrula_;
    C. _Dulus dominicus_; D. _Phainoptila melanoxantha_;
    E. _Phainopepla nitens_; F. _Ptilogonys cinereus_;
    G. _Ptilogonys caudatus_.
    a. femur; b. tibiotarsus; c. tarsometatarsus; d. total.]


_Arm-trunk Percentages._--Tables 1 and 2 show the total length of the
arm, and lengths of the separate arm elements, relative to the trunk.
Table 3 gives the corresponding lengths for birds other than the
Bombycillidae. Total length of arm was obtained by adding together the
lengths of the humerus, ulna, and manus, and by dividing the figure
thus obtained by the length of the trunk as was done for leg lengths
in tables 4 and 5. The method of adding together the component parts
does not give the entire length of the wing, since the length of the
feathers, which add effectively to the total length, as well as do the
lengths of the small carpal elements, is lacking.


  [Illustration: Figs. 45-46. Outlines of wings. × 1/2

    45. _Ptilogonys caudatus_, showing relation of outline of wing
        to bones of arm.

    46. _Bombycilla cedrorum_, showing relation of outline of wing
        to bones of arm.]


It may be noted that _Phainoptila_ and _Bombycilla_ have the shortest
arm in the family Bombycillidae. The humerus, radius and ulna are
comparable to the same elements in thrushes and the catbird, and it is
only the extremely short manus in _Phainoptila_ that affects the
total. The manus in _Phainoptila_ is comparatively smaller than in any
other genus of the family Bombycillidae, and this indicates poor
flight power. _Bombycilla_ has a total length corresponding closely to
that in warblers, but the lengths of the distal elements correspond
closely to those in the catbird and thrushes. Of the three segments,
the humerus is, relatively, the most shortened. Next in order of
increasing length of arm is _Dulus_; measurements for it are roughly
the same as those of _Myadestes_. The wing bones of the
Ptilogonatinae, other than _Phainoptila_, are the longest in this
series, and they most nearly resemble the same bones in flycatchers,
Parids, and gnatcatchers.


  [Illustration: Fig. 47. Graph showing relative lengths of bones of
                 the arm. The percentage values are shown on the axis
                 of the ordinates.

    A. _Bombycilla cedrorum_; B. _Bombycilla garrula_;
    C. _Dulus dominicus_; D. _Phainoptila melanoxantha_;
    E. _Phainopepla nitens_; F. _Ptilogonys cinereus_;
    G._ Ptilogonys caudatus_.
    a. humerus; b. radius; c. ulna; d. manus; e. total.]


It is notable that, in general, birds with long and narrow wings
appear to have relatively the shortest humeri, with the distal bones,
especially the manus, variable in length and seemingly correlated with
the manner of feather attachment. Those birds with rounded and short
wings have the longest humeri. In swallows, for example, the humerus
is short, whereas the other arm bones are long, and the manus is
unusually large and heavy. A short humerus gives better lever action
in the flight stroke than a long humerus does.




MUSCULATURE


Dissections showed the same muscles to be present in all genera of the
Bombycillidae. There are, nevertheless, differences in the size of the
muscles in the various species, and these differences have been
investigated primarily as a check on differences noted in the
structure of the bones. Even slight differences in mass can be
important functionally, but the difficulty in accurately measuring the
mass prevents wholly reliable conclusions. The method first used in
the attempt to determine the mass of a given muscle was that of
immersing the muscle in a liquid-filled graduated tube, and then
measuring the amount of liquid displaced. This method, although
adequate for large muscles, was subject to a great amount of error in
the case of small muscles, and consequently was abandoned. The
technique eventually used was that previously employed by Richardson
(1942). It consisted of dissecting out the muscle, placing it in
embalming solution, leaving it there until a later period, and
finally, weighing the muscle on scales, accurate to a milligram, after
the muscle had been out of the liquid for a period of one minute.
After being weighed, the muscle was measured by the displacement
method in a graduated tube, as a check. The results indicate that,
although the two methods give the same general results, weighing is
accurate to one-hundredth of a gram, whereas the displacement method
was accurate to only a tenth of a gram.

In determining the percentage of the weight of a muscle in relation to
the total weight of the bird, the weight of the muscle was used as the
numerator, and the weight of the preserved specimen was used as the
denominator. Before weights were taken, all specimens were plucked in
identical fashion.


_Caudal Muscles._--The muscles of the caudal area that were used for
comparison were the levator caudae and the lateralis caudae. These
muscles are used by the living bird to maintain the position of the
pygostyle and therefore the rectrices; these muscles are especially
important to those birds that utilize the tail as a rudder in flight
and as a brake. As may be seen by reference to Table 11, the two
muscles are largest in proportion to body weight in the
Ptilogonatinae, in which subfamily the species have long rectrices and
must have correspondingly well-developed muscles in order to utilize
the rectrices to best advantage in flight. The lateralis caudae
differs more according to species than does the levator caudae,
showing that rudder action of the tail is of primary importance in the
adaptation for capturing insects. It will be remembered that the
pygostyle in this subfamily has a flattened lateral surface for
attachment of the levator caudae muscle, and it is therefore to be
expected that this muscle will be larger in the Ptilogonatinae than it
is in either the Bombycillinae or the Dulinae. The levator coccygis,
together with the two muscles mentioned above, is responsible for
elevation of the tail. The levator coccygis is less altered in
different species of the family than is the lateralis caudae. It may
be noted that the caudal muscles of _Dulus_ and _Bombycilla_
constitute a smaller percentage of the total weight of the bird than
in any of the genera in the subfamily Ptilogonatinae.


  [Illustration: Fig. 48. Caudal musculature, of _Phainopepla nitens
                 lepida_, in dorsal view. × 2.

    a. Levator coccygis; b. Levator caudae; c. Lateralis caudae;
    d. Lateralis coccygis; e. oil gland; f. dorsal tip of pygostyle.]


  Table 11. Caudal Muscles (Actual and Relative Weights)

  =============================================
          Species         | Levator | Lateralis
  ------------------------+---------+----------
  Ptilogonys caudatus     | .145g.  |  .022g.
                          | .092%   |  .045%
                          |         |
  Ptilogonys cinereus     | .030g.  |  .010g.
                          | .076%   |  .026%
                          |         |
  Phainopepla nitens      | .025g.  |  .008g.
                          | .096%   |  .029%
                          |         |
  Phainoptila melanoxantha| .040g.  |  .015g.
                          | .063%   |  .014%
                          |         |
  Dulus dominicus         | .028g.  |  .006g.
                          | .063%   |  .014%
                          |         |
  Bombycilla garrula      | .034g.  |  .010g.
                          | .048%   |  .014%
                          |         |
  Bombycilla cedrorum     | .026g.  |  .008g.
                          | .050%   |  .014%
  ---------------------------------------------


  Table 12. Weights of Muscles (These percentages expressed in terms
  of weights of the body)

  Key to Table
  A) Deltoid
  B) Thigh
  C) Peronus
  D) Gastrocnemius

  ====================================================================
     Species     |P. major|P. minor|   A    |   B    |   C   |   D
  ---------------+--------+--------+--------+--------+-------+--------
  Ptilogonys     | 2.42g. |  .29g. |  .55g. |        |       |
    caudatus     | 4.94%  |  .59   | 1.12%  |  .43g. | .15g. |
                 |        |        |        |  .88%  | .31%  |    .96%
  Ptilogonys     | 2.19g. |  .28g. |  .53g. |        |       |
    cinereus     | 5.57%  |  .71%  | 1.35%  |  .30g. | .08g. |
                 |        |        |           .71%  | .21%  |   1.02%
  Phainopepla    | 1.30g. |  .20g. |  .30g. |        |       |
    nitens       | 4.99%  |  .77%  | 1.15%  |  .28g. | .10g. |
                 |        |        |        | 1.12%  | .40%  |   1.42%
  Phainoptila    | 3.93g. |  .44g. |  .92g. |        |       |
    melanoxantha | 6.18%  |  .69%  | 1.45%  | 1.09g. | .48g. |
                 |        |        |        | 1.61%  | .75%  |   2.97%
  Dulus          | 2.09g. |  .22g. |  .50g. |        |       |
    dominicus    | 4.81%  |  .50%  | 1.15%  |  .73g. | .18g. |
                 |        |        |        | 1.68%  | .41%  |   1.01%
  Bombycilla     | 3.85g. |  .45g. |  .55g. |        |       |
    garrula      | 5.31%  |  .62%  |  .76%  |  .50g. | .15g. |
                 |        |        |        |  .69%  | .18%  |    .59%
  Bombycilla     | 2.58g. |  .35g. |  .50g. |        |       |
    cedrorum     | 5.00%  |  .68%  |  .97%  |  .37g. | .10g. |
                 |        |        |        |  .73%  | .19%  |    .83%
  ---------------+--------+--------+--------+--------+-------+--------


_Pectoral Muscles._--The pectoral set of muscles varies but little in
the family; flight power is seemingly not dependent upon size of
either the pectoralis major or pectoralis minor. The data indicate
that the insertion on the humerus, with consequent changes in the
relative length of that bone, is more significant in type of flight
and over-all flight power than is the actual size of the muscle mass.
The deltoid muscle, for example, is smaller in _Bombycilla_ than in
members of the other two subfamilies. The humerus in _Bombycilla_ is
shortened, and the muscle therefore does not need to be large to
accomplish the same powerful stroke that would be accomplished by a
longer humerus and a larger, more powerful deltoid muscle. In the case
of the deltoid, the shortening of the humerus and the more complex
arrangement of the points of insertion have obviated the necessity of
enlarging the muscle.


_Leg Musculature._--The muscles of the thigh are noticeably larger in
birds that have long leg bones. (See Table 12 for size of muscles.) On
the tibiotarsus, the peroneus and gastrocnemius muscles were measured.
When expressed as a percentage of the weight of the bird, the peroneus
has much the same relative weight in all but one of the species,
whereas the gastrocnemius varies much. The peroneus is proportionately
large only in _Phainoptila_, in which genus all the leg muscles are
well developed, but the gastrocnemius is larger in all the
Ptilogonatinae and in _Dulus_ than it is in the specialized
_Bombycilla_, in which it has probably been reduced as the leg bones
and other muscles have been reduced.

The volume of the muscles of the hind limb changes more readily in
response to saltation and running than do the muscles of the forelimb
to flying.




DIGESTIVE TRACT


The digestive tract is relatively uniform in all genera of the family;
there are only slight differences between the species. The degree of
compactness of the visceral mass varies, _Phainoptila_ and _Ptilogonys
caudatus_ having the folds of the digestive tract loosely arranged,
whereas _Ptilogonys cinereus_ and _Phainopepla_ have folds which
adhere more tightly to the ventriculus and liver. In _Dulus_ and
_Bombycilla_, as compared with the Ptilogonatinae, the visceral mass
(primarily liver and ventriculus) is situated more posteriorly in the
body cavity, and is more compact, and the intestine is more tightly
coiled.

The coiling of the intestine, if its degree of compactness is
disregarded, is nearly identical in the birds of the family; there are
four major loops between the ventriculus and the anus. The length of
this section of the tract is, however, somewhat variable, as can be
seen by reference to Table 13, in which the actual and relative
lengths of the intestine are given. It may be seen that in
_Bombycilla_ and in _Phainopepla_, the tracts are much shortened. This
is notable, since these are frugivorous birds, and in many frugivorous
birds, the tract is lengthened for better extraction of edible
portions of the food. Possibly the action of the digestive juices is
correspondingly more rapid in _Bombycilla_ and _Phainopepla_, thereby
permitting the necessary nutriment to be extracted by a short
digestive tract.

In a migratory bird, or one that depends on flight power to find food
and escape capture by predators, as in the case of the waxwings, the
compacted and shortened visceral mass would seem to be advantageous,
because of the consequent reduction in weight. I consider the longer
intestine to be the ancestral condition, and that the intestine has
become shorter to meet new environmental conditions.


  Table 13. Digestive Tract: Actual Length, and Length Relative to
  Thoracic Length

  =========================+========+==============
                           |        |   Relative
           Species         | Length |    length
                           | in mm. | (in percent)
  -------------------------+--------+--------------
  Ptilogonys caudatus      |   134  |    476.9
  Ptilogonys cinereus      |   111  |    415.6
  Phainopepla nitens       |    94  |    357.5
  Phainoptila melanoxantha |   150  |    457.1
  Dulus dominicus          |   130  |    451.0
  Bombycilla garrula       |   102  |    298.2
  Bombycilla cedrorum      |    95  |    309.5
  -------------------------+--------+--------------


Beddard (1898:30) states that caecae in the tract may be highly
variable in a single family of birds. The Bombycillidae is no
exception in this regard. At the junction of the cloaca and the large
intestine, there are two small caecae, the function of which is
unknown to me. The caecae are largest in the Ptilogonatinae, smaller
in the Bombycillinae, and smallest in the Dulinae. There may be a
correlation between large caecae and more insectivorous diet and small
caecae and frugivorous diet; however, the data are not conclusive in
this regard.




ORIGIN OF THE SPECIES


It is here postulated that the center of origin for the ancestral
stock of the Bombycillidae was in a region of North America, which at
the time concerned was temperate or possibly even semi-tropical in
climate. Probably Northern Mexico was the place and probably the
climate was temperate. It is reasonably certain, because of the
distribution of the species of the family, that they originated in the
Americas. In the absence of paleontological data (_Bombycilla_ alone
is reported, in essentially its modern form, from the late
Pleistocene--Wetmore, 1940a), the place and time of origin cannot
certainly be determined.

The distribution of the family is such that the more primitive groups
are in the south. These are the Ptilogonatinae in Central America and
Mexico, and the isolated Dulinae in Haiti and the Dominican Republic.
This distribution would support the view that the origin was in the
south. However, the Holarctic Bombycillinae are so typically birds of
northern latitudes that, were it not for such close relatives south of
their range, it would appear logical to infer a northerly origin with
a subsequent shifting of populations both southward and northward. The
phyletic age of the family is probably great, however, as evidenced by
the spotty distribution of the birds.

In the evolution of this family, population pressure possibly played
the initial role in forcing members of the primitive, southern stock
to seek habitable areas on the periphery of the range. Some birds
also, being possessed of the "adventuresome spirit", aided the
northerly movement, thus effecting an extension of the breeding ranges
to the north. So far as is now known, this family did not seek living
space in South America. By extending its range, a species might find
more abundant food and nesting sites. This process of extending the
range probably would be costly to the species concerned, because only
those individuals best able to adapt themselves to the new
environmental conditions would be able to survive long enough to
reproduce their kind.

The return flight to the south could, in time, be dispensed with,
except in the coldest weather or when the local berry- and fruit-crop
failed. Birds such as waxwings are, of course, able to subsist on
dried fruits and berries in the critical winter season when strictly
insectivorous birds, not so catholic in their food habits, must return
south. It appears that waxwings are descendants of migratory birds
that have adjusted themselves to a life in the north; and they are
judged not to have evolved from year-round residents of the north.

Even a short migratory journey in spring by part of a population of
birds, while the other part remained in the original range, would
quickly isolate one breeding population from the other, resulting in
the formation of different genetic strains that lead to subspecies,
species, and finally to genera and families. Any variation away from
the ancestral, "sedentary" stock would become established more quickly
because of such isolation at the breeding period. By the same token,
the parental stock can, and no doubt does, become modified to suit its
environment more perfectly, thus accelerating the tempo of this type
of divergent evolution.

The original "split" of the Bombycillines is thought then to have been
the result of migration on the part of some of the ancestral stock,
with subsequent loss of regular migration because the need to return
south was lost. Early in development, and before the migrational
tendency was entirely lost, an isolated population, which later became
sedentary, as it was an island population, diverged to give rise to
the Dulinae. The Dulinae are a homogeneous group since on the islands
now inhabited by the birds, they have not been isolated sufficiently
long to produce even well-marked subspecies.


  [Illustration: Fig. 49. Hypothetical family tree of the
                 Bombycillidae.]


The present day _Phainoptila_ is most nearly like the ancestral group,
and the remainder of the Ptilogonatinae have diverged to fit
conditions similar to those to which the Tyrannid flycatchers, which
parallel them, are also fitted.

In comparatively recent geological time, two basic lines developed
from the Bombycilline stock, the future _B. garrula_ and _B.
cedrorum_. Possibly _garrula_ originally was isolated in Europe and
Asia, and later came into contact with _B. cedrorum_, following the
time at which the two species were genetically well differentiated. It
appears certain that _B. japonica_ was an offshoot of the Bombycilline
stock at an early time, since it has characteristics that seem
relatively unspecialized. It possibly was isolated in the Orient.

Structural affinities of _Dulus_ and _Bombycilla_ are more pronounced
than are those of _Dulus_ and _Ptilogonys_, for example. Many of the
structural features of _Dulus_ parallel those of _Phainoptila_, and it
seems likely that the Dulinae were separated early in the history of
the family, perhaps as an isolated offshoot of the early migratory
Bombycillinae.




CONCLUSIONS


Nomenclature, as used by a taxonomist, should of course indicate
affinities as well as apply a name, and the rank of the family should
be applied to a structural unit based on common anatomical characters
that are more fundamental than, in my opinion, are those used by
Ridgway (1904) in proposing family status for the silky flycatchers
and the palm-chats. The characters in the diagnosis (page 478) of the
family Bombycillidae are common features regarded as warranting a
single family unit for the waxwings, silky flycatchers, and
palm-chats. The differences in morphology used by previous workers to
characterize each of these groups: (1) the silky flycatchers; (2)
waxwings and; (3) palm-chats are regarded as more properly characters
of only subfamily rank.

The existing coloration of the species of the Bombycillidae appears to
have been acquired relatively late, geologically speaking. The three
subfamilies responded to ecological stimuli in three different ways,
and the resulting color patterns are unlike in the three groups.
Dulinae to this day have a color pattern that is most like the
ancestral color pattern, and this is recapitulated in the juvenal
plumage of the Bombycillinae before they attain their adult plumage.

Consideration of the geographic distribution of the species of the
family indicates that the center of origin of the family Bombycillidae
was south of the present range of the waxwings (subfamily
Bombycillinae). Waxwings probably are the descendants of a migratory
population that diverged from the primitive population at an early
time in the history of the family. Owing to their adaptations to
survive in the north, waxwings no longer return south in the autumn.
Palm-chats (subfamily Dulinae) are descendants of an isolated
population of the family stock that developed communal living habits
as one specialization. Silky Flycatchers (subfamily Ptilogonatinae)
became modified to catch insects, and have specializations that
roughly parallel those of the Tyrannid flycatchers.

Osteologically, the various species of the Bombycillidae are
remarkably similar. Small variations do exist, but these are primarily
differences in relative size. The modifications of the beak enable
palm-chats to feed on parts of plants, and the beak of _Phainoptila_
shows some similarity in this respect. Rounded wings, which cause a
bird to fly by means of short, relatively weak strokes, are correlated
with a comparatively long humerus, whereas long and pointed wings,
which enable a bird to fly with more powerful strokes of the wing, are
correlated with a relatively short humerus. There is a positive
correlation between a short humerus and a long external condyle, and
between a long humerus and the absence or smallness of the external
condyle.

In the Bombycillidae short bones of the leg are adaptive, and long
bones of the leg are the generalized condition. Although all passerine
birds were differentiated relatively late in geologic time, long hind
limbs still could have been present in the immediate ancestors of
passerine birds. As adaptive radiation took place in the class Aves,
some birds, the Bombycillidae included, became more and more adapted
for an arboreal, and eventually an aerial habitat, with consequent
loss of saltatorial and running ability.

Birds, like mammals, have a short femur, the most proximal element in
the leg, if the species is adapted to run fast. If the species is not
adapted to run fast, birds, unlike mammals, have the tibiotarsus
longer than any of the other elements; in mammals that are not adapted
to run fast, the femur and tibia are approximately the same length. In
non-running birds as compared with running birds, the leg element
distal to the tibiotarsus, and the one proximal to it, are
considerably shortened. In waxwings, all three elements of the hind
limb are shortened, indicating that the reduction in length has been,
evolutionarily speaking, a rapid process, in order to reduce the limbs
to a convenient size as soon as possible.

The shape of the pygostyle varies in the Bombycillidae, but the simple
shieldlike bone of _Phainoptila_ is judged to resemble closely the
ancestral type. In _Ptilogonys_ there is a tall dorsal spine, coupled
with a wide and heavy centrum and flattened lateral areas, for support
of the long rectrices. In _Bombycilla_ the bone is small with knobs on
the centrum that have been developed for muscle attachment.

The muscles were carefully dissected in each genus and in most of the
species. The same homologous muscles are present in all species.
Significant differences were found only in the relative size of
certain muscles. No satisfactorily accurate method of measuring these
differences was found. Consequently, less use was made of the results
of the dissections than was originally planned.

The set of pectoral muscles varies but slightly in relative mass, and
the variation is not considered significant. The deltoid muscle was
selected for measurement since its point of insertion is unusually
variable, while the mass of the muscle varies little. We can conclude
that the extent of the area of insertion of the tendon of a muscle can
determine that muscle's relative efficiency, while the muscle itself
remains the same in bulk.

The muscles of the hind limb are notably larger in species that have
long legs, and a good index of the hopping ability may be gained by
study of certain of these muscles. In the Bombycillidae, and in those
Ptilogonatinae that do not use the hind limbs for hopping, the bones
are shortened, and the associated muscles are correspondingly smaller.

The gross anatomy of the digestive tract is practically identical in
the members of the family. The variability noted is mainly in the
degree of compactness of the visceral mass in _Bombycilla_ and in
_Phainopepla_. Also there is a tendency for the Bombycillinae and the
Dulinae to have the mass situated more posteriorly than it is in the
Ptilogonatinae. Moreover, _Bombycilla_ has a shorter intestine than do
the other genera. All of this indicates that the waxwings
(Bombycillinae) have the center of gravity situated more
advantageously for flight than do the birds of the two other
subfamilies.




SUMMARY


1. The silky flycatchers, waxwings, and palm-chats are included in the
family Bombycillidae; the Ptilogonatidae and Dulidae are reduced to
subfamily rank.

2. The coloration of the birds of each subfamily is different because
the ecological needs are different.

3. Waxwings were at one time regularly migratory, but are now nomadic,
since they are adapted to live in northern latitudes for the entire
year.

4. The corresponding bones in different members of the family closely
resemble one another, and the differences which do exist are the results
of responses within relatively recent times to changes in habits.

5. In the Bombycillidae a rounded wing is judged to be the primitive
condition. As the wing becomes more pointed, the humerus becomes shorter
and its external condyle longer.

6. The hind limbs are short in birds that depend most on flight power,
but are longer and the distal elements are disproportionately longer in
birds that depend on saltation or on running.

7. The pygostyle varies in shape and size between genera and even
between some species.

8. The pectoral muscles differ in size only slightly in the different
members of the family, but the insertions are more extensive for these
muscles in birds that fly a great deal.

9. The muscles of the hind limb vary in mass, but not in kind, in the
members of the family Bombycillidae.

10. In the Bombycillidae that depend on flight power, rather than on
saltation or on running power, there is a tendency for the digestive
tract to become shorter and for the whole visceral mass to become more
compact.




BIBLIOGRAPHY


ANDERSON, E. M.

    1915.  Nesting of the Bohemian Waxwing in northern British
           Columbia. Condor, 17(4):145-148, 1915.

ANDERSON, M. P.

    1907.  A collecting trip in Korea. Condor, 9(5):146-147, 1907.

ANDERSON, R. M.

    1909.  Nesting of the Bohemian Waxwing (_Bombycilla garrulus_).
           Auk, 26(1):10-12, 1909.

ARMSTRONG, E. A.

    1942.  Bird display. Cambridge Univ. Press, xvi + 381 pp.,
           22 plates, 1942.

BAIRD, S. F.

    1860.  The birds of North America. J. B. Lippincott Co., lvi
           + 1003 pp., 1860.

BEDDARD, F. E.

    1898.  The structure and classification of birds. Longmans, Green
           & Co., xx + 548 pp., 252 figs., 1898.

BERGTOLD, W. H.

    1917a. A study of the incubation period of birds. Kendrick-Bellamy
           Co., 109 pp., 1917.

    1917b. Regurgitation in the Bohemian Waxwing. Auk, 34(3):341-342,
           1917.

    1924.  A summer occurrence of the Bohemian Waxwing in Colorado.
           Auk, 41(4):614, 1924.

BOULTON, R.

    1926.  Remarks on the origin and distribution of the Zonotrichiae.
           Auk, 18(3):326-332, 1926.

BURLEIGH, T. D.

    1921.  Breeding birds of Warland, Lincoln County, Montana. Auk,
           38(4):552-565, 1921.

BURT, W. H.

    1930.  Adaptive modifications in the woodpeckers. Univ. California
           Publ. Zoöl., 32(8):455-524, 29 figs. in text, 1930.

CARRIKER, M. A., JR.

    1909-1912. An annotated list of the birds of Costa Rica including
           Cocos Island. Ann. Carnegie Mus., 6(1):314-915, 1909-1912.

CORY, C. B.

    1886.  The birds of the West Indies, etc. Auk, 3(2):187-245, 1886.

CROUCH, J. E.

    1936.  Nesting habits of the Cedar Waxwing. Auk, 53(1):1-8, 1936.

    1943.  Distribution and habitat relationships of the Phainopepla.
           Auk, 60(3):319-333, 1943.

ENGELS, W. L.

    1938.  Cursorial adaptations in birds--limb proportions in the
           skeleton of _Geococcyx_. Jour. Morph., 63:207-217, 3 figs.
           in text, 1938.

    1940.  Structural adaptations in Thrashers (Mimidae: Genus
           _Toxostoma_) with comments on interspecific relationships.
           Univ. California Publ. Zoöl., 42(7):341-400, 24 figs.
           in text, 1940.

FARLEY, J. A.

    1924.  Abnormal Cedar Waxwing. Auk, 41(1):160, 1924.

FISHER, H. I.

    1946.  Adaptations and comparative anatomy of the locomotor
           apparatus of New World Vultures. Amer. Midl. Nat.,
           35:545-727, 14 plates, 42 tables, 28 figs. in text, 1946.

FRANK, F.

    1939.  Die Färbung der Vogelfeder durch Pigment und Struktur.
           Jour. für Orn., 87:426-523, 1939.

GARROD, A. H.

    1876.  On some anatomical peculiarities which bear upon the major
           divisions of the passerine birds, Pt. I. Proc. Zoöl. Soc.
           London, 626-647, 1876.

GERONDET, P.

    1948.  Le jaseur boreal en Suisse pendant l'hiver 1946-1947. Der
           Orn. Beob., 45(1):1-5, 1948.

GOULD, J.

    1862.  The birds of Great Britain. London, published by the author,
           5 vols., text unpaged, 367 plates, 1862.

GRINNEL, J.

    1901.  The status of the Cedar Waxwing in California. Condor,
           3(6):146-147, 1901.

    1909.  A new cowbird of the genus _Molothrus_. Univ. California
           Publ. Zoöl., 5:275-281, 6 figs. in text, 1909.

GRISCOM, L.

    1934.  The ornithology of Guerrero, Mexico. Mus. Comp. Zoöl. Bull.
           75:367-422, 1934.

HAMILTON, W. J., JR.

    1933.  A late nesting waxwing in central New York. Auk,
           50(2):114-115, 1933.

HANNA, W. C.

    1931.  Nesting of the Bohemian Waxwing in British Columbia. Condor,
           33(6):253-254, 1 fig., 1931.

HEINROTH, O.

    1924.  Die Vögel Mitteleuropas. Berlin, Huge Bermühler, 1:51-58,
           1924.

HELLMAYR, C. E.

    1935.  Catalogue of the birds of the Americas. Field Mus. Nat.
           Hist. Mus. Publ. 347, 8(pt. 8):vi + 541 pp., 1935.

HOWELL, A. B.

    1938.  Muscles of the avian hip and thigh. Auk, 55(1):71-81,
           2 figs. in text, 1938.

    1944.  Speed in animals, their specialization for running and
           leaping. Univ. Chicago Press, xi + 270 pp., 55 figs. 1944.

HUDSON, G. E.

    1937.  Studies on the muscles of the pelvic appendage in birds.
           Amer. Midl. Nat., 18:1-108, 26 plates, 1937.

    1948.  Studies on the muscles of the pelvic appendages in birds
           II, the heterogeneous order Falconiformes. Amer. Midl. Nat.,
           39(1):102-127, 1948.

KNOWLTON, F. H.

    1909.  Birds of the world. Henry Holt & Co., Ltd., xi + 873 pp.,
           15 plates, 233 figs. in text, 1909.

KONODA, N.

    1943.  A dictionary of animals. Tokyo, 3 + 767 + 50 pp., profusely
           illustrated, 1943.

KOSHANTSCHIKOV, I.

    1930.  Ein Beitrag zur Kenntnis der Okologie, Biologie, und
           Geographie des Zobels (_Martes zibellina_ L.). Zeits. für
           Okol. der Tierre, 19(2):291-320, 2 maps, 1930.

LINSDALE, J. M.

    1928.  Variations in the Fox Sparrow (_Passerella iliaca_) with
           reference to natural history and osteology. Univ. California
           Publ. Zoöl., 30(12):251-392, 4 plates, 38 figs. in text,
           1928.

LITTLEFIELD, M. J., and LEMKAN, F.

    1928.  History of a Cedar Waxwing family. Bull. NE Bird-Band.
           Assoc., 4:85-89, 1928.

LUCAS, F. A.

    1897.  The tongues of birds. U. S. Nat. Mus. Report for 1895,
           1001-1019 pp., 2 plates, 1897.

MCGREGOR, R. C.

    1906.  Notes on birds observed while traveling from Yokohama to
           Manila. Condor, 8(4):98-100, 1906.

MATTHEW, W. D.

    1939.  Climate and evolution. N. Y. Acad. Sci., Spec. Publ.,
           1:xi + 223 pp., 1939.

MAYR, E.

    1942.  Systematics and the origin of species. Columbia Univ. Press,
           xiv + 334 pp., 29 figs. in text, 1942.

    1947.  Ecological factors in speciation. Evolution, 1(4):263-288,
           1947.

MERRIAM, F. A.

    1896.  Nesting habits of _Phainopepla nitens_ in California. Auk,
           8(1):38-43, 1896.

MILLER, A. H.

    1933.  Postjuvenal molt and the appearance of sexual characters of
           plumage in _Phainopepla nitens_. Univ. California Publ.
           Zoöl., 38(13):425-444 pp., 8 pls., 1 fig. in text, 1933.

    1937.  Structural modifications in the Hawaiian Goose (_Nesochen
           sandvicensis_). A study in adaptive evolution. Univ.
           California Publ. Zoöl., 42(1):1-80, 6 plates, 12 figs. in
           text, 1937.

    1941.  Speciation in the avian genus Junco. Univ. California Publ.
           Zoöl., 44(3):173-434, 33 figs. in text, 1941.

MULLER, C. S.

    1915.  A northern winter record of the Phainopepla. Condor,
           17(3):129, 1915.

MYERS, H. W.

    1907.  Nesting habits of _Phainopepla nitens_. Condor, 9(4):101-103,
           1907.

    1908.  Observations on the nesting habits of _Phainopepla_.
           Condor, 10(2):72-75, 1908.

    1909.  Notes on the habits of _Phainopepla nitens_. Condor,
           11(1):22-23, 1909.

NEWTON, A., and GADOW, H.

    1893-1896. A dictionary of birds. Adams and Charles Black,
           xii + 1086 pp., 1893-1896.

NICE, M. M.

    1940.  Observations on the behavior of a young Cedar Waxwing.
           Condor, 43(1):58-64, 1940.

OBERHOLSER, H. C.

    1917.  A synopsis of the races of _Bombycilla garrula_ (Linnaeus).
           Auk, 34(3):330-333, 1917.

PEMBERTON, J. R.

    1908.  Northern range of the _Phainopepla_. Condor, 10(6):238, 1908.

PLATH, K.

    1933.  Molt of the Nonpareil. Auk, 50(2):121, 1933.

POST, K. C.

    1916.  The Cedar Waxwing (_Bombycilla cedrorum_) during July and
           August, 1916. Wilson Bull., 28:175-193, 1916.

RAND, A. L., and RAND, R. M.

    1943.  Breeding notes on _Phainopepla_. Auk, 60(3):333-341, 1943.

RICHARDSON, F.

    1942.  Adaptive modifications for trunk foraging in birds. Univ.
           California Pub. Zoöl., 46(4):317-368, 2 plates, 16 figs.
           in text, 1942.

RIDGWAY, R.

    1904.  The birds of North and Middle America, Part III. U. S. Nat.
           Mus. Bull. 50:xx + 801 pp., 19 plates, 1904.

SAUNDERS, A. A.

    1911.  A study of the nesting of the Cedar Waxwing. Auk,
           28(3):323-329, 1911.

    1912.  The probable breeding of the Bohemian Waxwing in Montana.
           Condor, 14(6):224, 1912.

SHARPE, R. B.

    1885.  Catalogue of the birds in the British Museum, Vol. 10,
           British Mus., xiii + 682 pp., 12 plates, 1885.

SHAW, W. T., and CULBERTSON, A. E.

    1944.  A flock of Cedar Waxwings meets tragedy. Condor,
           46(4):205-206, 1944.

SHUFELDT, R. W.

    1887.  A review of the muscles used in the classification of birds.
           Jour. Comp. Med. and Sur., 8(4):321-344, 1887.

    1889a. Comparative osteology of the families of North American
           birds. Jour. Morph., 3(1):81-114, 6 plates, 1889.

    1889b. Studies on the Macrochires, morphological and otherwise,
           with the view of indicating their relationships and
           defining their several positions in the system. Linn. Soc.
           London, Jour., 20(122):299-394, 1889.

    1890.  The myology of the Raven. Macmillan & Co., x + 344 pp.,
           76 figs., 1890.

    1909.  Osteology of birds. New York State Mus. Bull., 130:381 pp.,
           1909.

SKUTCH, A.

    Manuscript--unpublished notes and personal correspondence.

STEVENSON, H.

    1882.  On the plumage of the waxwing, _Ampelis garrulus_, Linnaeus,
           from the examination and comparison of a large series of
           specimens killed, in Norfolk, in the winter of 1866-'67.
           Trans. Norfolk and Norwick Naturalists' Soc., 3:326-344,
           2 figs. in text, 1882.

SUTTON, G. M., and BURLEIGH, T. D.

    1940.  Birds of Las Vigas, Veracruz. Auk, 57(2):234-243, 1940.

    1942.  Birds recorded in the Federal District and States of Puebla
           and Mexico by the 1939 Semple Expedition. Auk,
           59(3):418-423, 1942.

SWARTH, H. S.

    1922.  Birds and mammals of the Stikine River region of northern
           British Columbia and southeastern Alaska. Univ. California
           Publ. Zoöl., 24(2):125-314, 8 plates, 34 figs. in text, 1922.

TAYLOR, W. P.

    1918.  Bohemian Waxwing (_Bombycilla garrulus_) breeding within
           the United States. Auk, 35(2):226-227, 1918.

TAVERNER, P. A.

    1934.  Birds of Canada. Nat. Mus. Canada Bull., 72, series 19,
           445 pp., 77 plates, 488 figs. in text, 1934.

WAYNE, A. T.

    1924.  A remarkable Cedar Waxwing. Auk, 41(3):485, 1924.

WETMORE, A.

    1926.  The migrations of birds. Cambridge, Harvard Univ. Press,
           vii + 217 pp., 1926.

    1932.  Notes from Dr. R. Ciferri on the birds of Hispaniola. Auk,
           49(1):101-108, 1931.

    1940a. A check-list of the fossil birds of North America. Smithson.
           Misc. Coll., 99(4):1-88 pp., 1940.

    1940b. A systematic classification of the birds of the world.
           Smithson. Misc. Coll., 99(7):1-11 pp., 1940.

WETMORE, A., and SWALES, B. H.

    1931.  The birds of Haiti and the Dominican Republic. U. S. Nat.
           Mus. Bull. 155:iv + 482 pp., 26 plates, 1931.

WHEELOCK, I. G.

    1905.  Regurgitation feeding of nestlings. Auk, 22(1):54-71, 1905.

WHITTLE, H. G.

    1928.  The biography of a Cedar Waxwing. Bull. NE Bird-Band. Assoc.,
           4:77-85, 1928.

WOLFSON, A.

    1945.  The role of the pituitary, fat deposition, and body weight
           in bird migration. Condor, 47(3):95-127, 1945.

WOLLEY, J. J.

    1857.  On the nest and eggs of the Waxwing (_Bombycilla garrula_
           Tamm.). Proc. Zoöl. Soc. London, 25:55-56, 1857.


  _Transmitted July 29, 1949._


Mention should be made here of an important paper by Jean Delacour and
Dean Amadon (1949). The Relationships of _Hypocolius_ (Ibis,
91:427-429, plates 19 and 20) which appeared after the present paper
by Arvey was written. Delacour and Amadon stated that _Hypocolius_, a
monotypic Persian genus, should be assigned to the Bombycillidae.
Their conclusions (_op. cit._:429) were as follows: "It might be
advisable to set up three subfamilies in the Bombycillidae, one for
_Bombycilla_, one for _Hypocolius_, and a third for the silky
flycatchers, _Ptilogonys_, _Phainopepla_ and _Phainoptila_. Further
study may show that _Dulus_ can be added as a fourth subfamily.

"Previously the Bombycillidae appeared to be an American group of
which one genus (_Bombycilla_) had reached the Old World. Inclusion of
_Hypocolius_ in the family makes this theory uncertain. Without
obvious affinities to other families, and consisting of a small number
of scattered and rather divergent genera, the Bombycillidae would seem
to be a declining group whose origin cannot safely be deduced from the
distribution of the few existing species."

                                                              --Eds.


                               23-1019




UNIVERSITY OF KANSAS PUBLICATIONS


The University of Kansas Publications, Museum of Natural History, are
offered in exchange for the publications of learned societies and
institutions, universities and libraries. For exchanges and information,
address the EXCHANGE DESK, UNIVERSITY OF KANSAS LIBRARY, LAWRENCE,
KANSAS, U. S. A.

MUSEUM OF NATURAL HISTORY.--E. Raymond Hall, Chairman, Editorial
Committee.

This series contains contributions from the Museum of Natural History.
Cited as Univ. Kans. Publ., Mus. Nat. Hist.


 Vol. 1. 1. The pocket gophers (genus Thomomys) of Utah. By Stephen D.
            Durrant. Pp. 1-82, 1 figure in text. August 15, 1946.

         2. The systematic status of Eumeces pluvialis Cope, and
            noteworthy records of other amphibians and reptiles from
            Kansas and Oklahoma. By Hobart M. Smith. Pp. 85-89.
            August 15, 1946.

         3. The tadpoles of Bufo cognatus Say. By Hobart M. Smith.
            Pp. 93-96, 1 figure in text. August 15, 1946.

         4. Hybridization between two species of garter snakes.
            By Hobart M. Smith. Pp. 97-100. August 15, 1946.

         5. Selected records of reptiles and amphibians from Kansas.
            By John Breukelman and Hobart M. Smith. Pp. 101-112.
            August 15, 1946.

         6. Kyphosis and other variations in soft-shelled turtles.
            By Hobart M. Smith. Pp. 117-124. July 7, 1947.

         7. Natural history of the prairie vole (Mammalian genus
            Microtus). By E. W. Jameson, Jr. Pp. 125-151, 4 figures
            in text. October 6, 1947.

         8. The postnatal development of two broods of great horned
             owls (Bubo virginianus). By Donald F. Hoffmeister and
             Henry W. Setzer. Pp. 157-173, 5 figures in text.
             October 6, 1947.

         9. Additions to the list of the birds of Louisiana.
             By George H. Lowery, Jr. Pp. 177-192. November 7, 1947.

        10. A check-list of the birds of Idaho. By M. Dale Arvey.
            Pp. 193-216. November 29, 1947.

        11. Subspeciation in pocket gophers of Kansas. By Bernardo
            Villa-R. and E. Raymond Hall. Pp. 217-236, 2 figures in
            text. November 29, 1947.

        12. A new bat (genus Myotis) from Mexico. By Walter W. Dalquest
            and E. Raymond Hall. Pp. 237-244, 6 figures in text.
            December 10, 1947.

        13. Tadarida femorosacca (Merriam) in Tamaulipas, Mexico.
            By Walter W. Dalquest and E. Raymond Hall. Pp. 245-248,
            1 figure in text. December 10, 1947.

        14. A new pocket gopher (Thomomys) and a new spiny pocket
            mouse (Liomys) from Michoacán, Mexico. By E. Raymond Hall
            and Bernardo Villa-R. Pp. 249-256, 6 figures in text.
            July 26, 1948.

        15. A new hylid frog from eastern Mexico. By Edward H. Taylor.
            Pp. 257-264, 1 figure in text. August 16, 1948.

        16. A new extinct emydid turtle from the Lower Pliocene of
            Oklahoma. By Edwin C. Galbreath. Pp. 265-280, 1 plate.
            August 16, 1948.

        17. Pliocene and Pleistocene records of fossil turtles from
            western Kansas and Oklahoma. By Edwin C. Galbreath.
            Pp. 281-284, 1 figure in text. August 16, 1948.

        18. A new species of heteromyid rodent from the Middle
            Oligocene of northeastern Colorado with remarks on the
            skull. By Edwin C. Galbreath. Pp. 285-300, 2 plates.
            August 16, 1948.

        19. Speciation in the Brazilian spiny rats (genus Proechimys,
            Family Echimyidae). By João Moojen. Pp. 301-406,
            140 figures in text. December 10, 1948.

        20. Three new beavers from Utah. By Stephen D. Durrant and
            Harold S. Crane. Pp. 407-417, 7 figures in text.
            December 24, 1948.

        21. Two new meadow mice from Michoacán, México. By E. Raymond
            Hall. Pp. 423-427, 6 figures in text. December 24, 1948.

        22. An annotated check list of the mammals of Michoacán,
            México. By E. Raymond Hall and Bernardo Villa R.
            Pp. 431-472, 5 figures in text. December 27, 1949.

        23. Subspeciation in the kangaroo rat, Dipodomys ordii.
            By Henry W. Setzer. Pp. 473-573, 27 figures in text,
            7 tables. December 27, 1949.

        24. Geographic range of the hooded skunk, Mephitis macroura,
            with description of a new subspecies from Mexico.
            By E. Raymond Hall and Walter W. Dalquest. Pp. 575-580,
            1 figure in text. January 20, 1950.

        25. Pipistrellus cinnamomeus Miller 1902 referred to the genus
            Myotis. By E. Raymond Hall and Walter W. Dalquest.
            Pp. 581-590, 5 figures in text. January 20, 1950.

        26. A synopsis of the American bats of the genus Pipistrellus.
            By E. Raymond Hall and Walter W. Dalquest. Pp. 591-602,
            1 figure in text. January 20, 1950.

        Index. Pp. 605-638.


 Vol. 2. (Complete) Mammals of Washington. By Walter W. Dalquest.
         Pp. 1-444, 140 figures in text. April 9, 1948.


 Vol. 3. 1. The Avifauna of Micronesia, its origin, evolution, and
            distribution. By Rollin H. Baker. Pp. 1-359, 16 figures in
            text. June 12, 1951.

         2. A Quantitative study of the nocturnal migration of birds.
            By George H. Lowery, Jr. Pp. 361-472, 46 figures in text.
            June 29, 1951.

         3. Phylogeny of the waxwings and allied species. By M. Dale
            Arvey. Pp. 473-530, 49 figures in text, 13 tables.
            October 10, 1951.

       *       *       *       *       *


Transcriber's Notes:

The text herein presented was derived from scans of the original report
which were OCRed and proofread. Minor typographical errors (genus name
initial not italicized, missing parenthis, missing or superfluous
commas, etc.) were made but are not noted here. With the exception of
those corrections and those noted below, it is the same text.


Typographical Corrections

    Page 481              : Measureemnts => Measurements

    Page 486              : cedorum      => cedrorum

    Page 496, Fig. 11     : Luis         => Luís

    Page 480, 481         : Luis Potosí  => Luís Potosi

    Page 516, Table 12    : Gatrocnemius => Gastrocnemius


Emphasis Notation:

     _text_ : italicized

     =text= : bold

       *       *       *       *       *