Perognathus inornatusSan Joaquin pocket mouse

Geographic Range

San Joaquin pocket mice are found in California's central valleys, including the San Joaquin, Sacramento, and Salinas valleys, as well as the surrounding foothills of the western Sierra Nevada mountains and the western Mojave desert. (Hafner, et al., 1998; Linzey and Hammerson, 2009)


San Joaquin pocket mice are found in open grasslands, savanna, and desert shrub communities. They are most abundant in uncultivated areas and often live in areas with sandy washes and finely textured soils. Agriculture and urban development have displaced San Joaquin pocket mice from much of their native habitat. ("California Wildlife Habitat Relationships System", 1990; "Terrestrial Mammal Species of Special Concern in California", 1998; Hafner, et al., 1998)

  • Range elevation
    350 to 600 m
    1148.29 to 1968.50 ft

Physical Description

San Joaquin pocket mice have silky pelage without bristles and spines. The dorsal pelage is pale to pinkish, overlaid with blackish brown hairs. The ventral pelage is white and there are orange markings around the eyes. The tail, which is slightly larger than 50% of the total length, is bi-colored and relatively non-penicillate. Tail hairs extend less than 6 mm beyond the end of the tail. The antitragus of the ear is unlobed. San Joaquin pocket mice get their name from the fur-lined pockets in their cheeks that are used to store and transport seeds. Subspecies of P. inornatus differ in size of body, length of tail, coloration, and skull characteristics. ("San Joaquin Pocket Mouse", 2009; "Terrestrial Mammal Species of Special Concern in California", 1998; Best, 1993; Reid, 2006)

  • Sexual Dimorphism
  • male larger
  • Range mass
    7 to 12 g
    0.25 to 0.42 oz
  • Range length
    130 to 149 mm
    5.12 to 5.87 in


During estrus, females are involved in rushing, chasing, fighting, sunbathing, marking, digging, kicking, naso-anal contact, grooming, mounting, and escape leaping. Interaction between the sexes changes as the female passes through estrus. Mating involves one bout of mounting, afterwards the female twists onto her side and throws the male off. It is likely that males and females have multiple mates, but there is little information on the mating strategy. ("San Joaquin Pocket Mouse", 2009; Best, 1993)

The breeding season occurs from March to July, with the female having at least 2 litters of 4 to 6 offspring per year. The estrus cycle is 5 to 6 days in length. ("San Joaquin Pocket Mouse", 2009; Best, 1993)

  • Breeding interval
    Females have at least two litters per breeding season.
  • Breeding season
    San Joaquin pocket mice breed between March and July.
  • Range number of offspring
    4 to 6

The young are born in a burrow near the base of shrubs. They remain in the birthing den until mature. The length of time to maturity is unknown. Females invest heavily in offspring through gestation and lactation. Males are unlikely to contribute to offspring care. ("Stanislaus River Report", 1995; Linzey and Hammerson, 2009)

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


San Joaquin pocket mice have been observed living up to 10 years. Most probably live only one to a few years and most mortality probably occurs when individuals are less than 1 year old. (Reid, 2006)


San Joaquin pocket mice are nocturnal, foraging at night on the ground and spending the day below ground in a burrow. It is common to find some individuals active on the surface searching for food while most of the population is inactive. San Joaquin pocket mice hibernate in phases during autumn, winter, and spring. These phases depend on changes in the duration in torpor, which is influenced by the animals initial supply of energy. Episodes of euthermia between these phases are 2 to 3 times longer in the spring than in the winter. One of their most noticeable behaviors is the practice of sunbathing. Sunbathing involves digging at the ground with the forepaws, then lowering the cheek and extending the body. They alternate side rubs when sunbathing. Sunbathing spots of one animal, often located in one area, affect the behavior of the others and may have originated from a movement for spreading scent. A peri-anal drag, for scent marking, is accomplished by depressing the anal-genital area against the ground and walking forward. Seed gathering, transportation, burrowing, and den making are also behaviors of these animals. ("Terrestrial Mammal Species of Special Concern in California", 1998; Best, 1993)

Home Range

Information on home range sizes in San Joaquin pocket mice are unavailable.

Communication and Perception

Communication signals include the growl, squawl, and low grunt. Other forms of auditory communication include tooth-chattering and foot-drumming. Scent marking is also used. Touching is a highly used signal during mating. These animals perceive their environment through visual, tactile, acoustic, and chemical channels. (Best, 1993)

Food Habits

San Joaquin pocket mice are mainly granivorous, eating seeds of annual and perennial grasses, shrubs, and forbs. They will also eat soft-bodied insects, cutworms, earthworms, and even grasshoppers. In captivity they have been known to eat a mixture of parakeet seeds, rolled oats, sunflower seeds, and small amounts of leaves. Seeds and oats have been used to catch these animals live. They transport and store their food in fur-lined pockets in their cheeks. ("Stanislaus River Report", 1995; Best, 1993; Linzey and Hammerson, 2009; "Smithsonian National Museum of Natural History", 2009)

  • Animal Foods
  • insects
  • terrestrial worms
  • Plant Foods
  • seeds, grains, and nuts


San Joaquin pocket mice are preyed on by birds of prey, foxes, snakes, and feral cats. They are similar in color to their sandy surroundings, making it difficult for predators to see them. They are vigilant and seek safety when they detect a predator and are active at night to minimize their detection by predators. Through habitat destruction and the use of rodenticides, humans are the biggest threat to this species currently. ("Terrestrial Mammal Species of Special Concern in California", 1998)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Little is known about the ecosystem role of San Joaquin pocket mice because of extensive loss of their natural habitat. They are prey for their predators and they are themselves predators of small invertebrates. They may disperse seeds and help aerate the soil through burrowing. ("Terrestrial Mammal Species of Special Concern in California", 1998)

Economic Importance for Humans: Positive

San Joaquin pocket mice are important members of native ecosystems and their predation on insects may impact agricultural pests.

Economic Importance for Humans: Negative

There are no adverse effects of San Joaquin pocket mice on humans.

Conservation Status


Justin LaMasters (author), University of Oregon, Stephen Frost (editor), University of Oregon, Tanya Dewey (editor), University of Michigan-Ann Arbor, Catherine Kent (editor), Special Projects.



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


uses sound to communicate


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.


uses smells or other chemicals to communicate


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.

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.


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.

female parental care

parental care is carried out by females


Referring to a burrowing life-style or behavior, specialized for digging or burrowing.


an animal that mainly eats seeds


An animal that eats mainly plants or parts of plants.


having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.


the state that some animals enter during winter in which normal physiological processes are significantly reduced, thus lowering the animal's energy requirements. The act or condition of passing winter in a torpid or resting state, typically involving the abandonment of homoiothermy in mammals.


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).


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.


active during the night


the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.


specialized for leaping or bounding locomotion; jumps or hops.

scent marks

communicates by producing scents from special gland(s) and placing them on a surface whether others can smell or taste them


remains in the same area


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

soil aeration

digs and breaks up soil so air and water can get in


lives alone

stores or caches food

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


uses touch to communicate


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).


Living on the ground.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.


A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.


uses sight to communicate


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


California Department of Fish and Game. California Wildlife Habitat Relationships System. 17996. Sacramento, California: California Interagency Wildlife task Group. 1990. Accessed September 24, 2009 at

U.S. Department of the Interior, Bureau of Land Management California. San Joaquin Pocket Mouse. 2929. Bakersfield, California: U.S. Department of the Interior, Bureau of Land Management California. 2009. Accessed September 26, 2009 at

Smithsonian Institution. 2009. "Smithsonian National Museum of Natural History" (On-line). North American Mammals: Perognathus inornatus. Accessed September 24, 2009 at

California Department of Fish and Game. Stanislaus River Report. 4411. Stockton, California: Bay Delta and Special Water Projects Division. 1995. Accessed September 24, 2009 at

California Department of Fish and Game. Terrestrial Mammal Species of Special Concern in California. 31. Sacramento, California: Philip V. Brylski. 1998. Accessed September 24, 2009 at

Best, T. 1993. "The American Society of Mammalogists- Clark Science Center" (On-line pdf). Mammalian Species: Perognathus inornatus. Accessed September 26, 2009 at

Hafner, D., E. Yensen, G. Kirkland, Jr.. 1998. "Google Books" (On-line). North American rodents: status survey and conservation action plan. Accessed September 24, 2009 at

Linzey, A., G. Hammerson. 2009. "IUCN Red List of Threatened Species" (On-line). Perognathus inornatus. Accessed September 24, 2009 at

Reid, F. 2006. "A field guide to mammals of North America, north of Mexico" (On-line). Accessed December 01, 2009 at