Tamias obscurus

Geographic Range

California chipmunks, Tamias obscurus , can be found throughout the San Bernardino and San Jacinto mountains of southern California in a series of disjunct populations. Their range also extends southward, across desert ranges into Baja California, reaching as far south as the Sierra de San Francisco.

• Biogeographic Regions
• nearctic nearctic
  • native native

Habitat

They are typically found at elevations between 760 and 600 m (Callahan, 1977). These chipmunks occupy lower Sonoran, upper Sonoran, transition, and Canadian life zones (Best and Granai, 1994). Their habitat can also be described by the botanical wildlife in the areas; usually these are pinyon-juniper or pine-oak forests, often with manzanita or sage, and nearby rocky outcroppings (Best and Granai, 1994). North of San Gorgonio Pass, T. obscurus is replaced by Tamias merriami at elevations above pinyon-juniper habitat. However, the opposite occurs in communities south of San Gorgonio Pass. Tamias obscurus occurs alone in the Santa Rosa Mountains (Callahan, 1977).

• Habitat Regions
• temperate temperate
• terrestrial terrestrial

• Terrestrial Biomes
• forest forest
• scrub forest scrub forest
• mountains mountains

Physical Description

Through much of their range, California chipmunks are indistinctly colored. During the warmer summer months, the head is pale gray shaded with cinnamon, bordered on the sides with snuff brown, extending down to the snout as clay-redbrown. The facial stripes are dark brown, with blackish stripes around the eyes, offset by paler-gray stripes. On the dorsal side of the trunk, pelage has dark russet-brown stripes offset by a median pair of the pale gray stripes. The ventral pelage is creamy white. During the winter the pelage is very similar, but the dorsal stripes are more pronounced and the sides of the chipmunk become a pale brown (Best and Granai, 1994).

Average total length of these animals is 208 to 240 mm, of which the tail comprizes 91 to 99 mm. The hindfoot varies between 33 and 35 mm, and the weight varies betweeen 56 and 90 g (Callahan, 1977). Females are typically larger than males in cranium length, rostral length, zygomatic breadth, and several characters, but males have wider nasals than females (Best and Granai, 1994).

Tamias merriami , which has an overlapping range with California chipmunks, is superficially similar to T. obscurus . However, T. obscurus may be readily distinguished by the shape of the ossa genitalia, a longer hind foot, and a more rounded cranium. In the summer, T. obscurus also has paler adult pelage with less yellow with more reddish dorsal stripes than T. merriami (Callahan, 1977).

Unlike many other chipmunks, T. obscurus does not hibernate. If it does not become torpid, it is probably homoiothermic. All mammals are endothermic.

• Other Physical Features
• endothermic endothermic
• homoiothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• female larger

Reproduction

Not much is known about the mating behavior of T. obscurus . Males approach the female hesitantly, only after making the chip sound, and copulate several times often for more than a week (Best and Granai, 1994). If the pattern of other species in the genus holds for these animals, mating is likely to by polygynous.

The breeding season of T. obscurus is long, starting in January and extending into July (Best and Granai, 1994). During this season, a female can have more than two litters of 3 or 4 young each (Best and Granai, 1994). The gestation period for these chipmunks is approximately one month. The mothers often do not molt their winter pelage until after the young are independent (Callahan, 1976). Young are typically independent by the age of 8 weeks (Best and Granai, 1994).

Although there are no data for this species, in other members of the genus Tamias , the young reach independence during the season of birth, and are capable of breeding in the following breeding season. It is likely that T. obscurus is similar to other members of the genus in this regard.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• viviparous viviparous

Tamias obscurus males generally return to their burrows after the breeding season, and stay there until fall (Best and Granai, 1994). They play no role in parental care. Females, however, provide the young with protection and nourishment. They often move their young to a tree den or an underground burrow and often leave their young before they are 8 weeks old (Best and Granai, 1994).

• Parental Investment
• altricial altricial
• pre-fertilization
  • provisioning
  • protecting
    • female
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female
• pre-weaning/fledging
  • provisioning
    • female
  • protecting
    • female
• pre-independence
  • protecting
    • female

Lifespan/Longevity

There is little information published regarding longevity in this species, but one T. obscurus is known to have lived in captivity for 10 years (Best and Granai, 1994).

Behavior

This diurnal chipmunk is active throughout the year. The greatest amount of foraging and activity takes place in early morning and late afternoon. (Callahan, 1977). Tamias obscurus often creates burrows in logs or steep hillsides that are protected by the use of large boulders (Best and Granai, 1994).

• Key Behaviors
• terricolous
• diurnal diurnal
• motile motile
• sedentary sedentary

Home Range

Data are not available on the home range size of these animals. However, if they are like other members of the genus Tamias , males have slightly larger ranges than females.

Communication and Perception

Tamias obscurus uses vocalizations such as the chuck, trill, chatter, and chip (Blankenship and Brand, 1987). Calls are thought to be somewhat species specific, and may be a way for T. obscurus to recognize potential mates. Species specific vocalizations might play a role in reproductive isolation of sympatric species. (Blankenship adn Brand, 1987).

Although not specifically reported for this species, it is likely that California chipmunks use visual cues such as body positioning, tail position, and tail flicking in their communication, as these behaviors are common in most species in the genus. It can also be assumed that tactile communication occurs, especially during mating and between mothers and their offspring.

• Communication Channels
• visual visual
• tactile tactile
• acoustic acoustic

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

Food Habits

Similar to other chipmunks, T. obscurus likely subsists on a variety of seeds and fruits of grasses, forbs, and shrubs. Some of these items may include pinyon nuts, acorns, along with manzanita and juniper berries. They forage mostly along the ground and in shrubs, and often they will set up "feeding stations" perched on top of logs or rocks. Their food is probably also their main water source. (Callahan, 1977) These chipmunks are also known to cache food in their dens or burrows.

• Primary Diet
• herbivore herbivore
  • frugivore frugivore
  • granivore granivore

• Plant Foods
• seeds, grains, and nuts
• fruit

• Foraging Behavior
• stores or caches food stores or caches food

Predation

Reports of predation on these small mammals are not available. However, California chipmunks can use nearby rocks, logs, brush, and trees for cover and to hide from predators. Predation is likely to come from carnivorous animals such as hawks, foxes, and coyotes (Best and Granai, 1994).

• Anti-predator Adaptations
• cryptic cryptic

Ecosystem Roles

These chipmunks probably play some role in seed dispersal, as they transport seeds from the places they are found to feeding stations and food caches. They are likey to be important in local food webs, also, although the extent to which various predatory animals may depend upon them is not known.

• Ecosystem Impact
• disperses seeds

Economic Importance for Humans: Positive

These chipmunks have no known impact on humans.

Economic Importance for Humans: Negative

These chipmunks have no known negative impact on humans.

Conservation Status

These animals have a very limited distribution. As such, it is especially important to protect their habitat to ensure that the species will survive into the future.

Additional Links

Encyclopedia of Life

Contributors

Faith Chinnock (author), California State Polytechnic University, Pomona, Rebecca Cole (author), California State Polytechnic University, Pomona, John Demboski (editor, instructor), California State Polytechnic University, Pomona.

Nancy Shefferly (editor), Animal Diversity Web.

References

Best, T., N. Granai. 1994. Tamias obscurus . Mammalian Species , 472: 1-6.

Blankenship, D. 1999. California chipmunk| Tamias obscurus . Pp. 369-370 in The Smithsonian Book of North American Mammals . Washington and London: The Smithsonian Institution Press in Association with the American Society of Mammalogists.

Blankenship, D., L. Brand. 1987. Geographic Variation in Vocalizations of Tamias obscurus and T. merriami . Bulletin of Southern California Academy of Sciences , 86: 126-135.

Callahan, J. 1977. Diagnosis of Eutamias obscurus (Rodentia: Sciuridae). Journal of Mammalogy , 58: 188-201.

Callahan, J. 1976. Systematics and Biogeography of Eutamias obscurus . University of Arizona: Department of General Biology.