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Tamias obscurusCalifornia chipmunk

By Faith Chinnock and Rebecca Cole

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. (Best and Granai, 1994)

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). (Best and Granai, 1994; Callahan, 1977)

  • Range elevation
    760 to 2600 m
    2493.44 to 8530.18 ft

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. (Best and Granai, 1994; Blankenship, 1999; Callahan, 1977)

  • Sexual Dimorphism
  • female larger
  • Range mass
    56 to 90 g
    1.97 to 3.17 oz
  • Range length
    208 to 240 mm
    8.19 to 9.45 in

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. (Best and Granai, 1994; Blankenship, 1999)

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. (Best and Granai, 1994; Callahan, 1976)

  • Breeding interval
    These animals may breed twice during a year.
  • Breeding season
    Breeding season extends from January until July.
  • Range number of offspring
    3 to 4
  • Average gestation period
    1 months
  • Average time to independence
    8 weeks

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). (Best and Granai, 1994)

  • Parental Investment
  • 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).

  • Range lifespan
    Status: captivity
    10 (high) years

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). (Blankenship and Brand, 1987; Callahan, 1977)

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. (Blankenship, 1999)

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. (Blankenship and Brand, 1987)

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. (Blankenship, 1999; Callahan, 1977)

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

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

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. (Blankenship, 1999)

  • 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.

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.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

acoustic

uses sound to communicate

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chemical

uses smells or other chemicals to communicate

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

diurnal
  1. active during the day, 2. lasting for one day.
endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

frugivore

an animal that mainly eats fruit

granivore

an animal that mainly eats seeds

herbivore

An animal that eats mainly plants or parts of plants.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

motile

having the capacity to move from one place to another.

mountains

This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

native range

the area in which the animal is naturally found, the region in which it is endemic.

scrub forest

scrub forests develop in areas that experience dry seasons.

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

stores or caches food

places a food item in a special place to be eaten later. Also called "hoarding"

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

References

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

Blankenship, D. 1999. California chipmunk| Tamias obscurus . Pp. 369-370 in D Wilson, S Ruff, eds. 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.

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