Tamias umbrinus
Uinta chipmunk

Uinta chipmunks, Tamias umbrinus, are discontinously distributed in eight western states, including Nevada, Utah, northern Arizona, eastern California, northwestern Colorado, western and southern Wyoming, eastern Idaho, and southern Montana. Specific mountain ranges where T. umbrinus is found are the Beartooth Mountains in Montana; Uinta and Wasatch Mountains in Utah and Wyoming; Salt River, Wind River, Teton, and Absaroka Mountain ranges in Wyoming; Big Hole Mountains in eastern Idaho; and the Inyo, White, and Sierra Nevada mountains in eastern California and western Nevada. (Harris, Shellhammer, and Duke, 1988; Howell, 1929; Johnson, 1943b; Kays and Wilson, 2002; Streubel, 2000; Wilson and Ruff, 1999)

Tamias umbrinus inhabits moderate to high elevation coniferous forests (2000 to 3400 m) typically composed of spruce-fir, Douglas-fir, lodgepole pine, bristlecone, whitebark, ponderosa, limber, foxtail, or drier pinyon pine (Harris, 2004; Streubel, 2000; Montana Fish, Wildlife and Parks, 2005). These chipmunks favor locations near logs and brush in exposed timberline slopes and ridges. The species is primarily arboreal, dwelling in tree cavities where they may sleep or even nest. In addition, individuals of the species may burrow underneath shrubs and rock. (Harris, Shellhammer, and Duke, 1988; Johnson, 1943b; Streubel, 2000)

Tamias umbrinus is a medium-sized species of chipmunk with an average total body length of about 225 mm, and an average mass of 59 g. As in other species of Tamias, males are typically somewhat smaller than females. Five subspecies of T. umbrinus have been documented.

It can be difficult to distinguish Uinta chipmunks from other co-occurring species of chipmunks strictly by sight. However, one diagnostic pelage feature is that the light dorsal stripes are white and surround noticeably-broader brown, rather than black, dorsal stripes as in other species of Tamias. In addition, the medial dorsal stripe, unlike several other species of chipmunk, is not black but instead brownish-black. The outermost dark dorsal stripe is very faint or absent. Tamias umbrinus also possesses a dark-brown tail that is held horizontal while running. The ventral pelage is whitish and the flanks are generally brown or cinnamon in color. The species displays smoky gray-brownish pelage on the head and face regions, with blackish ocular stripes, brown submalar stripes, grayish white postauricular patches, and blackish and grayish white coloration on the anterior and posterior part of the ears, respectively. Winter and summer pelage do not differ significantly.

Like other species of chipmunks, T. umbrinus possesses large, fur-lined, cheek pouches for food storage. This enables individuals to gather and store food as they forage and then transport it back to caches for consumption during winter months. This derived characteristic distinguishes chipmunks from the other members of Scuridae. When danger approaches, chipmunks can run at full speed while still retaining the gathered food in their cheek pouches. (Harris, Shellhammer, and Duke, 1988; Howell, 1929; Montana Fish, Wildlife,, and Parks, 2004; Nowak, 1999)

Uinta chipmunks hibernate, and so are heterothermic. An individual's body temperature lowers during hiberation. However, because body temperature remains constant both in hibernation and when individuals are active, they are also homoiothermic. (Nowak, 1999)

The lifespan of Tamias umbrinus has not been recorded. However, most chipmunks do not live very long. A wild Tamias rufucaudus is reported to have lived for 8 years, and a captive Tamias townsendii lived over 10 years. Uinta chipmunks are likely to have maximum lifespans no greater than this. (Nowak, 1999)

Uinta chipmunks are diurnal and predominately tree-dwelling. Hibernation patterns are similar to other chipmunks in that prolonged sleep is not observed. Instead, chipmunks establish food caches and during winter months enter states of torpor from which they awake every several days to eat from the stored food supply. But T. umbrinus, unlike some other species of chipmunks, consumes extra food during the autumn in addition to storing food in caches. This probably increases the chances of surviving the winter months. Months of hibernation are typically from October to May, but may vary with region and elevation. (Harris, Shellhammer, and Duke, 1988; Montana Fish, Wildlife,, and Parks, 2004)

Home Range

Tamias umbrinus is non-migratory, with a home range of 100 to 457 meters. (Harris, Shellhammer, and Duke, 1988; Montana Fish, Wildlife,, and Parks, 2004)

Communication and perception in this species have not been reported. However, it is likely that Uinta chipmunks are like other western chipmunks in these areas. Most chipmunks use a combination of vocalizations and visual cues, such as body posture and tail positioning, in their communication. There is likely to be tactile communication during mating and rearing of young. The role of olfactory cues has not been examined. (Nowak, 1999)

Tamias umbrinus is omnivorous and spends the summer months searching for food in trees, snags, shrubs, and on the ground. In the autumn months, extra food is gathered and stored in underground caches to be used during the winter. Uinta chipmunks feed primarily on fruit, conifer mast, and seeds of maple, juniper, and chokecherry. In addition, fungi obtained by digging are a substantial part of ithe diet. Other items occasionally consumed include pollen, buds, insect larvae, and even bird eggs. (Harris, Shellhammer, and Duke, 1988; Montana Fish, Wildlife,, and Parks, 2004)

Predators of T. umbrinus include carnivorous mammals such as weasels, coyotes, foxes, bobcats, and birds such as raptors. (Harris, Shellhammer, and Duke, 1988)

Because chipmunks carry seeds from their source to caches, it is likely that these animals aid in the dispersal of various seeds. Any burrowing done aids in soil aeration. In addition, these animals provide a host for larval cuterebrid bot flies (Cuterebra fontinella).

Uinta chipmunks are not known to have negative effects on humans.

There is no direct economic impact of this species on humans. However, indirectly, these chipmunks may be beneficial. Because of their role in seed dispersal, they may help forests to regenerate.

Tamias umbrinus is a protected non-game species, but is not in danger of extinction and is fairly abundant where it occurs. (Streubel, 2000)

Several taxonomic changes have occured that are relevant for T. umbrinus. The genus, Tamias as a whole was formerly known as Eutamias. A sub-species once classified as Eutamius quadrivittatus inyoensis is now placed in T. umbrinus as T. umbrinus inyoensis (Johnson, 1943). It has been suggested that the genus be split into three subgenera, Neotamias, Eutamias, and Tamias, and that both T. umbrinus and T. palmeri be classified as subspecies of Neotamias umbrinus as N. u. umbrinus and N. u. palmeri (Piaggio, 2001).

Uinta chipmunks have been a model for study of territoriality, parapatry, and interspecific competitive exclusion. It has been noted that factors affecting the range of the species include its adaptation to arboreal life and social behavior (see Brown, 1971) or its suceptability to a parasite (Bergstrom, 1992). In the former study, competition with the more aggresive Tamias dorsalis was found to be minimal within the arboreal home range of T. umbrinus, whereas in areas of sparse growth T. dorsalis had a much easier time chasing off Uinta chipmunks. In Bergstrom's study, T. umbrinus was described as the more aggressive species, but showed a higher sensitivity to infestations of larval cuterebrid bot fly common in the lower-elevation territories of two other species. (Bergstrom, 1992; Brown, 1971; Johnson, 1943a; Piaggio and Spicer, 2001)