Mammals of the Grand Mesa, Colorado.

by Sydney Anderson.

The Grand Mesa of Colorado is a westward extension of the mountains of central Colorado, standing more than five thousand feet above the valleys of the Colorado and the Gunnison rivers. To certain montane mammals the mesa is a peninsula of cool, moist, forest surrounded by inhospitable, hot, dry, barren lowland.

Few mammals previously have been preserved or reported from the Grand Mesa. Of the species here reported, Warren (1942, The Mammals of Colorado, Univ. Oklahoma Press) mentioned only four from the counties in which the Grand Mesa is located. Twenty-two species are here recorded from the Grand Mesa, and two localities below the rim of the Mesa on the north slope, on the basis of specimens preserved, and five additional species on the basis of observations. Many of these species are limited to a montane habitat or find their optimum conditions there. The known geographic ranges of some subspecies are extended westward.

Specimens and notes were obtained by members of a field party from the Museum of Natural History led by Dr. Harrison B. Tordoff. The party, including also R. Gordon Cliffgard, John M. Legler, Olin L. Webb, and Glen E. Woolfenden, was in the area from June 17 to July 5, 1954, and obtained all of the specimens listed excepting those from 28 miles east of Grand Junction (Sect. 29, T. 11S, R. 95W), Mesa County, that were obtained from June 13 to July 2, 1956, by Phillip M. Youngman, and those from Land's End Road that were obtained on May 13 and 14, and on October 1, 1948, by D. A. Sutton.

Localities designated by numbers in the accounts to follow are listed in the legend for Figure 1. Localities 1 and 3 lie below the rim of the Mesa on the north side. Catalogue numbers are of the Museum of Natural History of the University of Kansas, unless noted otherwise.

=_Sorex cinereus cinereus_= Kerr.--Two male (59642-59643) Masked Shrews weighing 4.8 and 4.9 grams were trapped on June 17 at locality 10, and a nonpregnant female (59644) was trapped on June 26 at locality 6.

_Sorex cinereus_ seemed to be less abundant on the Mesa than _Sorex vagrans_; more individuals of _S. vagrans_ than of _S. cinereus_ were trapped on June 17 at locality 10 and on June 26 at locality 6, and _S.

vagrans_ was trapped at three localities where no _S. cinereus_ was obtained.

[Ill.u.s.tration: FIG. 1. Map of the Grand Mesa (for purposes of this paper the area above 7500 feet on each side of the northern boundary of Delta County). The inset of the western three-fourths of Colorado shows the Grand Mesa in relation to the larger areas of mountains in the state (areas above 9000 feet are stippled). The following collecting localities are indicated by numbered, black dots:

(1) 2 mi. N, 9 mi. E Collbran, 7000 ft., Mesa County.

(2) Land's End Road to Grand Mesa, 6800 to 8050 ft., Mesa County.

(3) 3 mi. E, 4 mi. S Collbran, 6800 ft., Mesa County.

(4) 3 mi. E, 9 mi. S Collbran, 10,200 ft., Mesa County.

(5) 5-1/2 mi. E, 11-1/2 mi. S Collbran, _in_ Delta County.

(6) 5-1/2 mi. E, 12 mi. S Collbran, 9600 to 10,400 ft., _in_ Delta County.

(7) 28 mi. E Grand Junction (Sec. 29, T. 11S, R. 95W), Mesa County.

(8) 6 mi. E Skyway, 10,000 to 10,500 ft., _in_ Delta County.

(9) 7 mi. E Skyway, _in_ Delta County.

(10) 8 mi. E, 1/2 mi. S Skyway, 9500 to 10,200 ft., _in_ Delta County.

(11) 8 mi. E, 3/4 mi. S Skyway, 10,200 ft., _in_ Delta County.

(12) 8 mi. E, 1 mi. S Skyway, 10,000 to 10,200 ft., _in_ Delta County.

(13) 8 mi. E, 1-1/2 mi. S Skyway, 8500 to 9600 ft., _in_ Delta County.

(14) 8 mi. E, 2 mi. S Skyway, 9000 ft., _in_ Delta County.

(15) 8 mi. E, 2-1/2 mi. S Skyway, 9600 ft., _in_ Delta County.

(16) 1 mi. S, 4 mi. W Skyway, 10,200 ft., Mesa County.]

=_Sorex vagrans obscurus_= Merriam.--Fifteen specimens of the Vagrant Shrew (59645-59655, 59665-59668) were trapped in Delta County from localities 6, 10, 12, 13, and 14. The fourteen specimens having skulls fell into two distinct age-cla.s.ses based on wear of the teeth as described by Findley (1955, Univ. Kansas Publ., Mus. Nat. Hist., 9:8); 5 were in the younger group and 9 in the older group. Weights in grams of the younger shrews were 4.6, 5.5, 5.7, 5.8, and 6.4; weights of the older shrews were 6.4, 6.8, 7.3, 7.4, 7.5, 8.0, 8.3, and 8.8. One of the seven females was lactating; none contained embryos.

=_Sorex pal.u.s.tris navigator_= (Baird).--Six Water Shrews (59633-59638) were trapped in Delta County at localities 10, 13, 14, and 15. The one specimen from locality 10 was trapped on June 17; all others were taken on June 21. None was pregnant or lactating. Two are young, weighing 11.0 and 12.9 grams; the other four are older, weighing 16.6, 17.0, 19.2, and 21.5 grams.

=_Myotis evotis evotis_= (H. Allen).--One female Long-eared Myotis (59671), containing no embryos, was shot at dusk on July 2, at locality 3, which is below the rim of the Mesa.

=_Myotis volans interior_= Miller.--One female Long-legged Myotis (70016), containing no embryos, was shot at locality 7 on July 1, 1956.

=_Ochotona princeps figginsi_= J. A. Allen.--Six specimens of the Pika (59672-59675, 70018-70019) from localities 5, 6, 7, 8, and 9 extend the known range of the subspecies approximately 55 miles to the westward from Irwin in Gunnison County. Each of two females taken on June 18 and 26 contained three embryos, which measured 20 millimeters in the latter; a third female on June 29 contained two embryos 35 millimeters in length.

=_Lepus america.n.u.s bairdii_= Hayden.--No Snowshoe Rabbit was taken, but one individual was observed by H. B. Tordoff on June 18, 1954, at locality 8. Droppings of a large lagomorph were seen in the woods, and tracks were seen in the snow.

=_Marmota flaviventris luteola_= A. H. Howell.--The seven specimens of the Yellow-bellied Marmot (59731-6, 70022, four adult and two young, each a skin and skull, and one skull only of an adult) are referable on the basis of size, color, and locality as discussed by Warren (1936, Jour. Mamm., 17:394) to _M. f. luteola_. The total lengths in millimeters are as follows: young male 582; adult males 640, 655; young females 460, 520; adult female 630. The color and condition of the pelage is the same in all the specimens except that the two largest males are much more worn and show irregular patches of new hair on the back, and the two young females are paler especially on the back and tail. These marmots were taken at localities 4, 7, 8, 10, and 16.

=_Spermophilus lateralis lateralis_= (Say).--Eleven specimens of the Golden-mantled Ground Squirrel (59748-59756, 59763-59764) were taken at localities 1, 3, and 4. Young were born before late June; three young of the year were taken at locality 3 on June 29 and 30, and none of the adult females taken at locality 1 (1 female) and at locality 4 (3 females) was pregnant. Most adults of both s.e.xes at all elevations represented (6800 to 10,200 ft.) showed molt in progress and proceeding from anterior to posterior. All specimens were obtained from June 25 to July 4.

=_Spermophilus variegatus grammurus_= (Say).--Three Rock Squirrels (59738-59739, 59742) were obtained at locality 3. One of these specimens was a skull found near a wood rat nest. The other two were nonpregnant females; the adult measured 485 millimeters in total length, and the younger individual measured 413 millimeters. The two skins are characteristic of _S. v. grammurus_ in their paleness.

=_Eutamias minimus consobrinus_= (J. A. Allen).--The 63 specimens of the Least Chipmunk (59770-59824, 60105-60108, 70024-70025, and nos.

5194 and 5196 in Univ. of Colorado Museum) were taken at localities 2, 3, 4, 6, 7, 8, 10, 13, and 15. The reproductive condition at time of death had been noted for 20 females obtained from June 17 to July 2 at elevations from 9500 to 10,400 feet. Eleven of these had no embryos, but six have mammae that are still prominent on the dried skins and may have had litters prior to their capture. Nine females contained embryos, numbering 3 in two specimens, 5 in four specimens, 6 in two specimens, and 7 in one specimen.

=_Eutamias quadrivittatus hopiensis_= Merriam.--Four specimens of the Colorado Chipmunk were obtained by D. A. Sutton at locality 2, at 6800, 6900, 7175, and 8050 feet elevation. All are males taken on May 13 and 14, 1949; the specimens bear numbers 5197, 5198, 5199, and 5201 in the collection of the University of Colorado Museum.

=_Th.o.m.omys talpoides fossor_= J. A. Allen.--The 27 specimens of the Northern Pocket Gopher (59840-59849, 70086-70102) were trapped at localities 3, 6, 7, 10, 11, and 13. The eight skins from locality 7 differ from those from the other localities on the Mesa in being uniformly duller in color dorsally. No significant difference in size or cranial characters was observed. Specimens a.s.signed to _T. t.

fossor_, in the collection of the Museum of Natural History, from other localities in Colorado differ in color from any of the specimens from the Grand Mesa. Until larger numbers of _Th.o.m.omys talpoides_ from other localities in Colorado and from the type locality of _T. t. fossor_, stated to be at Florida, in southern Colorado, have been studied, the specimens from the Grand Mesa seem best referred to _T. t. fossor_.

Three females from localities 7, 10, and 11 contained embryos (2, 4, and 5 in number), and seven other females from localities 6 and 7 show distinct mammae on the dried skins or were recorded by the collectors as lactating.

=_Castor canadensis concisor_= Warren and Hall.--Dams constructed by beavers were seen at locality 4 on June 23, 1954. No specimen was taken.

=_Peromyscus maniculatus rufinus_= (Merriam).--The 36 specimens of the Deer Mouse (59921-59956) are from seven localities (3, 4, 6, 10, 12, 14, and 15). The mice vary considerably in color; most of them are like mice of the highlands of Colorado and unlike the paler mice inhabiting the lower areas immediately to the west of the Grand Mesa. Young individuals trapped on June 20, 21, and 22 and judged to range from a month through two months in age, and females containing embryos, attest to a somewhat protracted breeding season on the Grand Mesa.

=_Neotoma cinerea arizonae_= Merriam.--Two immature Bushy-tailed Wood Rats (60000-60001) were obtained at locality 3 on July 3.

=_Clethrionomys gapperi galei_= (Merriam).--The 22 specimens (60005-60025, 70133) of Gapper's Red-backed Vole were taken at localities 6, 7, and 10, and are clearly referable to _C. g. galei_, rather than to _Clethrionomys gapperi gauti_ to the south, on the basis of generally dark dorsal pelage, indistinctly bordered broad dorsal stripe, and cranial features. _C. g. gauti_ was described by c.o.c.krum and Fitch (1952, Univ. Kansas Publ., Mus. Nat. Hist., 5:289) on the basis of 14 specimens from southern Colorado and northern New Mexico.

Twenty-one additional specimens from five miles south and one mile west of Cucharas Camps, Huerfano County, were obtained from the seventh to the fourteenth of July by the field party led by Tordoff after the party left the Grand Mesa. These specimens substantiate the subspecific distinctness of _C. g. gauti_ in that they agree in external and in cranial appearance with the description of typical _C. g. gauti_, and are distinct in appearance from specimens of _C. g. galei_ from the Grand Mesa and from other localities in northern Colorado. The six specimens from two localities in Colorado available to c.o.c.krum and Fitch exhibited evidence of intergradation at one locality, and atypical smallness at the other locality. A specimen (70134) taken on June 26, 1956, by Phillip M. Youngman on the Black Mesa, nine miles WNW of Sapinero, 9500 ft., Gunnison County, Colorado, is almost identical in color to the two specimens from Saguache County regarded by c.o.c.krum and Fitch as intergrades between _C. g. galei_ and _C. g. gauti_, but in small size of auditory bullae and narrowness of braincase resembles _C. g. galei_, to which it seems best referred. The specimens from the Grand Mesa extend the known range of _C. g. galei_ approximately 50 miles westward in central Colorado from Gothic. Three females were pregnant; two trapped on June 17 and June 25 contained 6 embryos each, and one trapped on June 25 contained 5 embryos. Four of the females taken in Huerfano County were pregnant; one contained 3 embryos, two contained 5 embryos, and one contained 7 embryos. Immature individuals are present in the sample from Huerfano County also.

=_Phenacomys intermedius intermedius_= Merriam.--Three Heather Voles (60048, 60049, 70135) were trapped at localities 6, 7, and 10. All were adult females; one, taken on June 25 at locality 6, contained seven embryos five millimeters in length, and one, taken on July 2 at locality 7, contained seven embryos nine millimeters in length. These specimens extend the known range of the species approximately 55 miles west from Gothic (Pruitt, Jour. Mamm., 35:450, 1954).

=_Microtus longicaudus mordax_= (Merriam).--Ten Long-tailed Voles (60070-60079) represent localities 3, 6, 12, 13, 14, and 15.

=_Microtus monta.n.u.s fusus_= Hall.--Ten Montane Voles (60060-60068, 70145) represent localities 3, 6, 7, and 15.

=_Ondatra zibethicus osoyoosensis_= (Lord).--Muskrats were seen daily from June 17 to June 23 in a lake at locality 13. No specimen was obtained.

=_Zapus princeps princeps_= J. A. Allen.--Nineteen Western Jumping Mice (60109-60126, 60137) were trapped at localities 6, 10, 12, 14, and 15.

=_Erethizon dorsatum epixanthum_= Brandt.--A Porcupine skull was seen in the nest of a wood rat by John M. Legler at locality 3 on July 2. On June 20 a porcupine was seen at locality 12. No specimen was obtained.

=_Mustela frenata nevadensis_= Hall.--Seven Long-tailed Weasels (60138-60143, 70152) were taken at localities 1, 4, 7, 8, 13, and 14.

Four are males and three are females. Some of these were attracted by "squeaking" noises and then shot.

=_Taxidea taxus taxus_= (Schreber).--One adult male Badger (60144) was found dead; the skull and baculum were saved. The subspecific identification is on geographic grounds, and is tentative. In this area _T. t. taxus_ and _T. t. fippsi_ may intergrade.

=_Mephitis mephitis estor_= Merriam.--One Striped Skunk (60145) of unknown s.e.x was found dead in the cellar of a cabin at locality 10.

=_Odocoileus hemionus hemionus_= (Rafinesque).--Mule Deer were observed at locality 15; no specimen was obtained.

DISCUSSION

The species here reported from the Grand Mesa may be placed according to their geographic ranges and their restriction to certain habitats in two groups:

BOREAL.--Each of the 12 species listed below is of northern distribution, is dependent, at the lat.i.tude of Colorado, upon the habitat provided by areas of high alt.i.tudes, and is near its southern zonal limit on the Grand Mesa. The 12 species are: _Sorex cinereus_, _Sorex pal.u.s.tris_, _Sorex vagrans_, _Ochotona princeps_, _Lepus america.n.u.s_, _Marmota flaviventris_, _Spermophilus lateralis_, _Clethrionomys gapperi_, _Phenacomys intermedius_, _Microtus longicaudus_, _Microtus monta.n.u.s_, and _Zapus princeps_. _Th.o.m.omys talpoides_ may be considered in this category also, although it is less restricted in range and habitat than most of the other species listed as boreal. These thirteen species make up almost half of the twenty-seven species known from the Grand Mesa.