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Chaetodipus intermediusrock pocket mouse

By John Maggirias

Geographic Range

Rock pocket mice occur in rocky habitats in the southwestern United States, from south-central Utah through much of Arizona, New Mexico, Texas (western Sonora, Chihuahua and Trans-Pecos), as well as northwestern Mexico (Wilson and Ruff, 1999; Weckerly et. al., 1985; Weckerly et. al., 1988).

Habitat

Rock pocket mice inhabit desert and are particularly associated with rocky areas. (Wilson and Ruff, 1999). Average home range size is 400 meters (Krebs et al., 1990).

Physical Description

Rock pocket mice range from 157 to 188mm in total length, with a tail length from 84 to 112mm. They weigh between 10.5g. and 19.9g. The tails are long and tufted at the tip (Wilson and Ruff, 1999). Their relative size is small in contrast to other members in their genus (Vaughn, 2000). Body size varies regionally (Weckerly et. al., 1988) Pelage is grayish brown on the back with pale orange brown lines on the sides and white underneath. Hairs are coarse with weak "spines" on the rump (Wilson and Ruff, 1999). The bottoms of their hind feet are bare to the heels (Wilson and Ruff, 1999). Dental formula is 1/1 0/0 1/1 3/3=20 and cheek teeth of are ever growing (Vaughn, 2000). Sexual dimorphism is observed, with males being larger overall and in certain morphological features such as mastoid width, nasal length, and mandible length (Wilson and Ruff, 1999; Weckerly et al., 1988).

  • Range mass
    10.5 to 19.9 g
    0.37 to 0.70 oz

Reproduction

The breeding season begins in February or March and progresses into July. Litter size varies from three to six (Wilson and Ruff, 1999). Similar to other species of pocket mice, rock pocket mice live for a maximum of three years (Paulson, 1988). Van de Graff (1975) observed that males tend to be in reproductive condition for longer periods each year than females. In southeastern Arizona all males captured from February until September were fertile. Females are reproductively active from February until the end of July. Males in reproductive condition averaged 2.3g. heavier than those that were not (Van de Graff, 1975). During prolonged droughts reproduction is often delayed and survivorship of young is 7.3% (Paulson, 1988).

  • Key Reproductive Features
  • gonochoric/gonochoristic/dioecious (sexes separate)
  • sexual

Behavior

Rock pocket mice are nocturnal. During colder periods they become torpid but may remain active for a period of two hours when temperatures are below freezing. They accomplish this by altering basal metabolic rate to be higher in colder temperatures (Wilson and Ruff, 1999).

Communication and Perception

Food Habits

Rock pocket mice are granivorous, feeding on a variety of seeds depending on availability (Rebar, 1995; Wilson and Ruff, 1999). They are capable of collecting seeds in fur-lined cheek pouches. Cheek pouch volume is directly proportional to body size (Vander-Wall et al., 1998).

Economic Importance for Humans: Positive

No literature available to identify positive economic importance to humans.

Economic Importance for Humans: Negative

No literature available to identify negative economic importance to humans.

Conservation Status

Contributors

John Maggirias (author), University of Toronto.

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

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

desert or dunes

in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.

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.

motile

having the capacity to move from one place to another.

native range

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

sexual

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

tactile

uses touch to communicate

References

Krebs, J., S. Healy, S. Shettleworth. 1990. Spatial memory of Rodents:Comparison of a storing and non-storing species.. Animal Behaviour, 39: 1127-1137.

Lee, T., M. Engstrom, J. Bickham. 1991. Banded chromosomes of four species of pocket mice (Rodentia: Heteromyidae). Texas J. of Sci., 43: 33-38.

Paulson, D. 1988. Chaetodipus baileyi. Mammalian Species, 297: 1-5.

Rebar, C. 1995. Ability of Dipodomys merriami and Chaetodipus intermedius to locate resource distributions. J. of Mammalogy, 76: 437-447.

Van de graff, K. 1975. Reproductive ecology of some Sonoran desert rodents. J. Mammalogy, 59: 503-507.

Vander-Wall, S., W. Pyare, J. Veech. 1998. Cheek pouch capacities and loading rates of heteromyid rodents. Oecologia, 113: 21-28.

Vaughn, R. 2000. Mammalogy 4th Edition. Canada: Harcourt Brace and Company.

Weckerly, F., T. Best. 1985. Morphological variation among rock pocket mice (Chaetodipus intermedius) from New Mexico lava fields. Southwestern Naturalist, 30: 491-501.

Weckerly, F., A. Gennaro, T. Best. 1988. Description of a new rock pocket mouse, Chaetodipus intermedius, from New Mexico. Southwestern Naturalist, 33: 100-102.

Wilson, D., S. Ruff. 1999. The Smithsonian Book of North American Mammals. Canada: UBC Pres..

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