Geographic Variation in Red-Backed Mice (genus Clethrionomys) of the Southern Rocky Mountain Region

Part 1

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Geographic Variation in Red-backed Mice (Genus Clethrionomys) of the Southern Rocky Mountain Region

E. LENDELL COCKRUM and KENNETH L. FITCH

University of Kansas Publications Museum of Natural History

Volume 5, No. 22, pp. 281-292, 1 figure in text November 15, 1952

UNIVERSITY OF KANSAS LAWRENCE 1952

~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. 22, pp. 281-292, 1 figure in text November 15, 1952

~University of Kansas~ Lawrence, Kansas

PRINTED BY FERD VOILAND, JR., STATE PRINTER TOPEKA, KANSAS 1952 [Illustration: Union Label] 24-4369

Geographic Variation in Red-backed Mice (Genus Clethrionomys) of the Southern Rocky Mountain Region

E. LENDELL COCKRUM and KENNETH L. FITCH

In the course of the preparation of a synopsis of the North American terrestrial microtines by one of us (Cockrum), and the completion of a Master's thesis on the geographical variation of the red-backed mice of Wyoming by the other (Fitch) we had occasion to study the red-backed mice of the southern Rocky Mountain region (see figure 1). Results of these studies are the recognition of two heretofore unnamed subspecies of the red-backed mouse in the southern Rocky Mountain region, and a clarification of the taxonomic status of two additional kinds.

+Clethrionomys gapperi galei+ (Merriam)

1890. Evotomys galei Merriam, N. Amer. Fauna, 4:23, October 8.

1931. Clethrionomys gapperi galei, Hall, Univ. California Publ. Zool., 37:6, April 10.

1897. Evotomys gapperi galei, Bailey, Proc. Biol. Soc. Washington, 11:126, May 13.

Type locality.--Ward, 9500 feet, Boulder County, Colorado.

Range.--The Rocky Mountains of extreme southern Alberta, Montana, northwestern and southern Wyoming, and north and central Colorado.

Remarks.--C. g. galei, with the largest geographic range of any of the Rocky Mountain subspecies, is also the most variable. Three principal areas of geographic variation were found. These areas are: The mountains of north-central Colorado and southern Wyoming (this area includes the type locality); the Big Horn area probably northwest into Montana (no adult specimens from Montana or Alberta examined); and the Teton area which includes the mountains east and southeast of Yellowstone National Park. Specimens from these areas have noticeable differences in pelage, but no constant cranial differentiation could be detected. Specimens from the Medicine Bow Mountains of southern Wyoming have a more reddish dorsal stripe, and more buff and less gray on the sides than either of the northern geographic variants. The dorsal stripe continues farther anteriorly and is better defined through its entire length. There are fewer differences between the two northern geographic variants than between either one of them and the southern variant. Specimens from the Teton Mountains, however, have grayer sides, and the outer margin of the ear is tipped with chestnut (little or no chestnut shows on the ears of the specimens from the Big Horn Mountains); the dorsal stripe is less distinct (with slightly more gray throughout) than in either of the other geographic variants of the one subspecies.

Three specimens (two adults) are available from the Little Medicine Range in Converse County (22 miles south and 24.5 miles west of Douglas, 7600 feet), Wyoming. Although red-backed mice probably are found in the mountains of Natrona and Albany counties, the population, in the Little Medicine Range is somewhat isolated. In coloration these mice are lighter than any of the three geographic variants described above; the dorsal stripe is narrower; the sides are more buffy; the dorsal stripe does not project anteriorly beyond the ears as it does in the specimens from the Medicine Bow Mountains; and the face is grayer. These specimens resemble the population in the Big Horn Mountains to the north more than the population in the Medicine Bow Mountains.

The specimens from the Little Medicine Range, the Big Horn Range, and the Tetons are possibly subspecifically distinct from the southern specimens. Examination of specimens now allocated to galei from Montana and Alberta should aid in revealing whether the northern animals are an unnamed subspecies.

Specimens examined.--Total, 167, distributed as follows and unless otherwise stated, in the collection of the University of Kansas Museum of Natural History:

+Wyoming+: Park County: 28 mi. N and 3 mi. W Cody, 7200 ft., 1. Big Horn County: Medicine Wheel Ranch, 28 mi. E Lovell, 9000 ft., 22; 17-1/2 mi. E and 4-1/2 mi. S Shell, 1. Teton County: Moran, 6244 ft., 4; Moran, 3 (James Findley Collection); 2-3/4 mi. E Moran, 6300 ft., 1; 3-3/4 mi. E and 1 mi. S Moran, 6200 ft., 10. Washakie County: 9 mi. E and 9 mi. N Tensleep, 8200 ft., 3; 9 mi. E and 4 mi. N Tensleep, 7000 ft., 1. Johnson County: 4 mi. W and 1 mi. S Klondike, 6500 ft., 1; 6-1/2 mi. W and 2 mi. S Buffalo, 5620 ft., 1. Lincoln County: 3 mi. N and 11 mi. E Alpine, 5650 ft., 1. Sublette County: 31 mi. N Pinedale, 8025 ft., 1. Fremont County: Togwotee Pass, 5 (James Findley Collection); 20-1/2 mi. W and 2 mi. S Lander, 1; Mocassin [=Moccasin] Lake, 19 mi. W and 4 mi. N Lander, 10,100 ft., 3; 18 mi. W and 3 mi. N Lander, 1; Mosquito Park Ranger Station, 17-1/2 mi. W and 2-1/2 mi. N Lander, 9500 ft., 10; 6-1/2 mi. W and 17 mi. S Lander, 8450 ft., 4; 5-1/2 mi. W and 22 mi. S Lander, 8800 ft., 3. Converse County: 22 mi. S and 24-1/2 mi. W Douglas, 7600 ft., 3. Carbon County: 18 mi. SW Rawlins, 7500 ft., 2; 19 mi. E and 8 mi. N Encampment, 9150 ft., 4; 19-1/2 mi. E and 6 mi. N Savery, 8800 ft., 1; 11 mi. E and 6 mi. N Savery, 8400 ft., 1; 14 mi. E and 6 mi. N Savery, 1. Albany County: 3 mi. ESE Browns Peak, 10,000 ft., 59.

+Colorado+: Rio Blanco County: 9-1/2 mi. SW Pagoda Peak, 7700 ft., 2. Boulder County: 2-1/2 mi. S Estes Park, 8400 ft., 2; 3 mi. S Ward, 8. Clear Creek County: 2 mi. S Idaho Springs, 8000 ft., 1. Gunnison County: Gothic, 8 mi. N Crested Butte, 6 (James Findley Collection).

Additional records.--+Colorado+: Rio Blanco Co.: 25 mi. NE Meeker (Cary, N. Amer. Fauna, 33:120, 1911). El Paso Co.: Lake Moraine, 10,250 ft. (Warren, Mammals of Colorado, p. 224, 1942).

~Fig. 1.~--Geographic ranges of the subspecies of Clethrionomys gapperi in the southern Rocky Mountains.

Part 2

+Clethrionomys gapperi brevicaudus+ (Merriam)

1891. Evotomys gapperi brevicaudus Merriam, N. Amer. Fauna, 5:119, July 30.

1897. Evotomys brevicaudus, Bailey, Proc. Biol. Soc. Washington, 11:129, May 13.

1942. Clethrionomys gapperi brevicaudus, Bole and Moulthrop, Sci. Publ. Cleveland Mus. Nat. Hist., 5:153, September 11.

Type locality.--Three miles N Custer, 6000 ft., South Dakota.

Range.--The Black Hills of South Dakota and Wyoming.

Remarks.--Merriam (N. Amer. Fauna, 5:119, July 30, 1891) named this subspecies on the basis of two specimens collected in the Black Hills of South Dakota in July, 1888, and assigned it to the species Evotomys [= Clethrionomys] gapperi. He reported the diagnostic characteristics as: "Similar to E. gapperi, but with larger ears and shorter tail. The hazel of the dorsal area is not so bright as in gapperi; the sides are the same golden brown." Of the cranial and dental characteristics he wrote: "Much as in E. gapperi."

Bailey (Proc. Biol. Soc. Washington, 11:129, May 13, 1897), in his "Revision of the American voles of the genus Evotomys," with one additional specimen available, raised the Black Hills population to specific status, re-emphasizing the shortness of the tail, and pointing out a few slight cranial differences ("zygomatic arches low and flaring out, so that the inner instead of the outer side shows in top view; auditory bullae as large as in gapperi, but less rounded").

Bailey (loc. cit.) remarked that: "though based on so scanty material, the characters distinguishing the species are fairly pronounced. Its range is isolated and widely separated from that of any other members of the genus by open prairie country and a wide belt of the Transition zone. There seems to be no valid reason for considering it a subspecies."

Additional specimens have been taken in recent years from the Black Hills of South Dakota and northeastern Wyoming. This material has shed light on the relationships and morphological characteristics of the red-backed mice of this region. Bole and Moulthrop (Sci. Publ. Cleveland Mus. Nat. Hist., 5:153, September 11, 1942) listed, as comparative material, eight specimens from Bull Springs, Custer County, South Dakota, under the name Clethrionomys gapperi brevicaudus (Merriam). They gave no reason for arranging brevicaudus as a subspecies of C. gapperi.

Twenty adults (11 skins and skulls, 9 skulls only) from Pennington County, South Dakota (specimens in the University of Michigan Museum of Zoology), have the following measurements (averages of external measurements based on 11 specimens only): Total length, 142 (123-155); tail, 35 (30-39); hind foot, 19.5 (18.6-21.0); basal length, 23.3 (21.7-24.5); condylobasilar length, 23.3 (21.9-24.5); zygomatic breadth, 13.7 (12.9-14.7); lambdoidal breadth, 11.7 (11.3-12.9); alveolar length upper cheek-teeth, 5.5 (5.2-5.8); interorbital breadth, 3.9 (3.6-4.1); length of nasals, 7.7 (7.1-8.5); breadth of rostrum, 3.2 (2.9-3.6); and length of incisive foramina, 5.0 (4.6-5.3).

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