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.
23–7438