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A New Subspecies of Microtus montanus from
Montana and Comments on Microtus
canicaudus Miller

BY

E. RAYMOND HALL and KEITH R. KELSON

University of Kansas Publications
Museum of Natural History
Volume 5, No. 7, pp. 73-79
October 1, 1951

University of Kansas
LAWRENCE
1951


UNIVERSITY OF KANSAS PUBLICATIONS, MUSEUM OF NATURAL HISTORY

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

Volume 5, No. 7, pp. 73-79
October 1, 1951

UNIVERSITY OF KANSAS
Lawrence, Kansas

PRINTED BY
FERD VOILAND, JR., STATE PRINTER
TOPEKA, KANSAS
1951

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A New Subspecies of Microtus montanus from Montana and Comments on
Microtus canicaudus Miller

BY

E. RAYMOND HALL AND KEITH R. KELSON


In 1949, for the Museum of Natural History of the University of Kansas,
Mr. John A. White collected two specimens of the species _Microtus
montanus_ in the Bitterroot Valley of Montana, that did not fit the
description of any named subspecies. These were laid aside until we
could examine the additional specimens from Montana in the Biological
Surveys collection in the United States National Museum, some of which
previously had been reported by Bailey (N. Amer. Fauna, 17:31, June 6,
1900) under the name _Microtus nanus canescens_ Bailey [=_Microtus
montanus canescens_]. Our examination reveals that the animals from the
Bitterroot and Flathead valleys belong to an heretofore unrecognized
subspecies which is named and described below.

     Microtus montanus pratincolus new subspecies

     _Type._--Female, adult, skull and skin, No. 34004, Univ. Kansas,
     Mus. Nat. Hist.; from 6 mi. E Hamilton, 3700 ft., Ravalli County,
     Montana; obtained on August 14, 1949, by John A. White; original
     number 477.

     _Geographic distribution._--Flathead and Bitterroot valleys of
     western Montana.

     _Diagnosis._--Size small for the species (see measurements). Color:
     Essentially as in _Microtus montanus nanus_. Skull: Small, slender,
     and comparatively smooth; rostrum moderately depressed distally;
     nasals moderately inflated distally and extending posteriorly not
     quite to tips of premaxillary tongues; nasals usually truncate
     posteriorly, but rounded in some individuals; premaxillary tongues
     terminating posteriorly in a short medial spine; zygomatic arches
     lightly constructed and usually more widely spreading posteriorly
     than anteriorly; interparietal comparatively long and terminating
     in a small, but distinct, medial spine, otherwise approximately
     rectangular in shape; exposed parts of upper incisors short and,
     for the species, only slightly procumbent; molar dentition weak
     and, in most specimens, especially so posteriorly; tympanic bullae
     large and well inflated, especially ventrolaterally; basioccipital
     narrow owing to the encroachment of the tympanic bullae.

     _Comparison._--Among named forms, _Microtus montanus pratincolus_
     most closely resembles _Microtus montanus nanus_. The geographic
     range of _M. m. nanus_ adjoins that of _M. m. pratincolus_ on three
     sides; there is no conspecific subspecies adjoining the range of
     _M. m. pratincolus_ on the north. From _M. m. nanus_, _M. m.
     pratincolus_ differs as follows (measurements are all of males,
     those of _M. m. nanus_ being of nine topotypes and near topotypes
     from central Idaho): size smaller (149 mm. as opposed to 165), tail
     shorter (37 as opposed to 39), hind foot shorter (19 as opposed to
     20), upper molar series shorter (expressed as a percentage of
     basilar length, 25.5 as opposed to 26.3), mastoidal region broader
     (expressed as a percentage of basilar length, 48.6 as opposed to
     46.7), braincase slightly more vaulted (depth of braincase
     expressed as a percentage of basilar length, 31.3 as opposed to
     30.4) and more inflated laterally; tympanic bullae more inflated,
     this inflation being the most conspicuous difference between the
     two subspecies. The tympanic bullae of _M. m. pratincolus_ have
     approximately a fourth more volume than those of _M. m. nanus_.

_Remarks._--Northwardly in the Bitterroot Valley, specimens of _M. m.
pratincolus_ morphologically approach _M. m. nanus_, especially in the
reduced degree of inflation of the tympanic portion of the bullae. On
geographic grounds we think that the geographic range of _M. m.
pratincolus_ extends southward to the southern end of the Bitterroot
Valley; we have not seen specimens from that area. Although we have not
examined the specimen reported upon by Davis (Murrelet, 18:26, September
4, 1937) from Canyon Creek, "a few miles west of Hamilton", Montana, we
think that it will be found to belong to _M. m. pratincolus_.

Our examination of specimens from localities in Montana east of the
range here ascribed to _M. m. pratincolus_ indicates that, among named
kinds of _Microtus_, those specimens are best referred to _M. m. nanus_.
These specimens are listed below under comparative materials. It should
be mentioned here that although Bailey (_loc. cit._) applied the name
_Microtus nanus canescens_ to Montanan specimens from Flathead Lake and
Hot Springs Creek, the subspecies _M. montanus canescens_ now is thought
to be restricted to Washington and the adjoining part of British
Columbia; _M. m. canescens_ does not occur so far east as Montana.

Grateful acknowledgment is made to those persons in charge of the
Biological Surveys collection for permission to study the specimens in
that collection, and to the Kansas Endowment Association for support of
the field work which yielded the specimens from six miles east of
Hamilton, Montana. The study here reported upon was aided also by a
contract between the Office of Naval Research, Department of the Navy,
and the University of Kansas (NR 161-791).

     _Measurements._--The following measurements in millimeters are
     those of the holotype and the average, maximum, and minimum,
     respectively, of eleven adult males from various places in the
     range of the subspecies. Except as noted below, we are unable to
     detect significant morphological differences in the populations
     sampled and believe that pooling of the measurements is justifiable
     in this case. Measurements are: Total length, 129, 149 (156-141);
     length of tail-vertebrae, 27, 37 (39-31); length of hind foot, 18,
     19 (20-18) (all preceding measurements are those of the
     collectors); basilar length, 22.2, 24.5 (25.7-23.4); greatest
     length of nasals, 6.7, 6.9 (7.4-6.4); zygomatic breadth, 14.2, 14.6
     (14.9-13.9); mastoidal breadth, 11.3, 11.8 (12.3-10.8); alveolar
     length of upper molar series, 6.0, 6.2 (6.5-5.9); depth of
     braincase (shortest distance from ventral surface of
     basioccipito-basisphenoidal suture to the dorsal surface of the
     cranium, and not perpendicular to the long axis of the skull), 7.7,
     7.7 (7.9-7.5); width of rostrum, 4.7, 4.8 (5.0-4.6); interorbital
     breadth, 3.2, 3.4 (3.6-3.2). Measurements of females, other than
     those of the holotype, are not given owing to the lack of
     sufficient material. Females, however, do not appear to differ
     appreciably in measurements from males.

     _Specimens examined_ (in U.S. Nat. Mus., Biol. Surv. Coll., except
     as otherwise indicated).--Total, 26, all from Montana, as follows:
     _Sanders Co._: Hot-springs Cr., 4. _Lake Co._: end of W arm
     Flathead Lake, 5; Ravalli, 8. _Ravalli Co._: Florence, 2; 8 mi. NE
     Stevensville, 4000 ft., 1; Corvallis, 4; 6 mi. E Hamilton, 3700
     ft., 2(K.U.).

     _Comparative materials_ (in U.S. Nat. Mus., Biol. Surv.
     Coll.).--_Microtus montanus nanus_: Total, 72, as follows: IDAHO:
     _Lewis Co._: Nez Perce, 3. _Idaho Co._: Seven Devils Mts., 3550
     ft., 3. _Custer Co._: Challis, 7; Pahsimeroi Mts. (9300 ft., 8;
     9700 ft., 4), 12. _Butte Co._: Lost River Mts., 1. _Canyon Co._:
     Nampa, 1; Bowmont, 1. _Ada Co._: Boise, 1. _Blaine Co._: Sawtooth
     Lake, 2; Alturas Lake, 3. _Owyhee Co._: Three Cr., 3. _Minidoka
     Co._: Heyburn, 2. _Bannock Co._: Pocatello, 4. _Bear Lake Co._:
     Montpelier Cr., 3. MONTANA: _Fergus Co._: Big Snowy Mts., 11.
     _Gallatin Co._: West Fork of West Fork, Gallatin River, 1. _Park
     Co._: Lamar River, 7000 ft., 2; Gardiner, 1. _Sweetgrass Co._:
     "near" head Big Timber Cr., Crazy Mts., 1; Big Timber Cr., 5200
     ft., Crazy Mts., 1; 14 mi. S Big Timber, 1; West Boulder Cr., 18
     mi. SE Livingston, 2; McLeod, 1. _Carbon Co._: Beartooth Mts., 2;
     Beartooth Lake, 1. WYOMING: _Park Co._: N end Lake, Yellowstone
     Nat'l Park, 2.


     Microtus montanus canicaudus Miller

     1897. _Microtus canicaudus_ Miller, Proc. Biol. Soc. Washington,
     11:67, April 21, type from McCoy, Willamette Valley, Polk County,
     Oregon.

In 1938 when one of us (Hall, Proc. Biol. Soc. Washington, 51:131-134,
August 23, 1938) arranged several nominal species of _Microtus_ as
subspecies of the species _Microtus montanus_, _Microtus canicaudus_ was
not included because that writer had not examined representative
specimens. In the U.S. Biological Surveys collection in the U.S.
National Museum we have examined specimens of _M. m. canicaudus_, all
from Oregon, as follows: Hood River (Catalogue Nos. 262583-262586);
Canby (262577, 262578); Wapinitia (79985-79988); Sheridan (69779,
69780); McCoy (75834-75842, 77744); Salem (246736); Albany (161554); and
Corvallis (242552). The four specimens from Wapinitia seem to be those
that Bailey (N. Amer. Fauna, 17:29, June 6, 1900) listed as _Microtus
montanus_. The diagnostic characters mentioned by Miller in the
original description (Proc. Biol. Soc. Washington, 11:67, April 21,
1897) included the following: size approximately the same as in
_Microtus [montanus] nanus_; upper parts yellowish; tail usually nearly
uniform grayish above and below; auditory bullae much inflated; lateral
pits at posterior edge of bony palate unusually shallow. Because the
tails of the original series were understuffed and variously rotated,
they seemed to be less sharply bicolored than is the case, as shown by
subsequently collected specimens. Otherwise we find that the characters
mentioned above differentiate _canicaudus_ from its nearest relatives,
_Microtus montanus canescens_ to the northward, _M. m. nanus_ to the
eastward, and _M. m. montanus_ to the southward. In _canicaudus_ we have
noted one additional differential character; the interpterygoid space is
acuminate anteriorly. In this feature and in each of the other features
mentioned above, intergradation with _Microtus montanus nanus_ is seen
in the specimens from Hood River and Wapinitia. In the specimens from
Hood River the auditory bullae are only slightly less inflated than in
those topotypes of _canicaudus_ having the smallest bullae; there is
appreciable variation in size of the bullae in the topotypes. Even so,
the minimum size of bullae among the topotypes is larger than the
maximum size in the specimens from Wapinitia. The four specimens from
Wapinitia have the yellowish color of _canicaudus_ to a considerable
degree, and show intergradation between _canicaudus_ and _nanus_ in
depth of the palatal pits and shape of interpterygoid space. The
slightly larger size of these specimens from Wapinitia suggests
intergradation with _M. m. montanus_. The tympanic bullae in the
specimens from Wapinitia seem to be smaller than in specimens of
_canicaudus_, _nanus_, or _montanus_.

Because of the intergradation described above between _Microtus montanus
nanus_ and _M. canicaudus_, the latter should stand as _Microtus
montanus canicaudus_.

      *      *      *      *      *

Bailey (N. Amer. Fauna, 55:206, August 29, 1936) recorded _canicaudus_
from Warm Springs in the Deschutes Valley of Oregon and from the state
of Washington. Other authors also have recorded _canicaudus_ from the
state of Washington. Our examination of specimens leads us to conclude,
as did Dalquest (Univ. Kansas Publ., Mus. Nat. Hist., 2:348, 349, April
9, 1948), that _canicaudus_ does not occur in Washington. The reported
occurrence of _M. canicaudus_ at Warm Springs, Deschutes Valley, Oregon,
seems to be the result of an error in identification. The specimens
concerned seem to be two _Microtus longicaudus mordax_ (Nos. 207060 and
207082 U.S.N.M.). They are labeled as collected at "Warm Springs (Mill
Cr.--20 Mi. W of)". Bailey's (_op. cit._, fig. 46, p. 209) map showing
the distribution in Oregon of _Microtus mordax mordax_ [=_Microtus
longicaudus mordax_] has a locality-dot at Warm Springs itself. Bailey
seems to have erred; he should have placed this dot 20 miles farther
west, we think. When preparing his map (_op. cit._, fig. 43, p. 205)
showing the geographic distribution of _Microtus canicaudus_, Bailey
seems to have misidentified these same two specimens as _M. canicaudus_,
and for them placed a locality-dot on his map 20 miles east (instead of
west) of Warm Springs. In brief, Bailey probably did not see any
specimens of _canicaudus_ or specimens of any other subspecies of
_Microtus montanus_ from Warm Springs.

_Transmitted February 15, 1951._


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