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San Joaquin pocket mouse

Perognathus inornatus

What do they look like?

San Joaquin pocket mice have silky soft fur that doesn't have any bristles or spines. The fur on their back is pale or pinkish, with dark brown hairs on top. The fur on their bellies is white, and they have orange markings around their eyes. Their tail is longer than the rest of its body, and is two colors. San Joaquin pocket mice get their name from the fur-lined pockets in their cheeks where they store and transport seeds. Their subspecies have different body sizes, tail lengths, colors, 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

Where do they live?

San Joaquin pocket mice live in the river valleys of central California, including the San Joaquin, Sacramento, and Salinas valleys. They also live at the bottom of the western Sierra Nevada mountains and the western Mojave desert. (Hafner, et al., 1998; Linzey and Hammerson, 2009)

What kind of habitat do they need?

San Joaquin pocket mice live in open grasslands, grasslands with trees called savanna, and areas with desert shrubs. They are most common in places that haven't been farmed. They live in places with sandy or fine soils. Farming and building more buildings have taken over a lot of their original 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

How do they reproduce?

During the time when females can mate, females chase, fight, sunbathe, mark territory, dig, kick, and groom themselves. Males and females probably both have more than one mate, but there isn't a lot of information available. ("San Joaquin Pocket Mouse", 2009; Best, 1993)

San Joaquin pocket mice breed from March to July. Females have at least 2 sets of 4 to 6 young every year. Females are able to mate during certain times, which usually last 5 to 6 days. ("San Joaquin Pocket Mouse", 2009; Best, 1993)

  • How often does reproduction occur?
    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

Young San Joaquin pocket mice are born in a burrow near the base of a shrub. They stay in their burrow until they mature. Females feed their young milk after they are born, so they invest a lot of effort in their young. Males probably don't contribute to caring for the young. ("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

How long do they live?

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 can live up to 10 years. Most of them probably live 1 to 3 years, and most of the deaths are before age 1. (Reid, 2006)

How do they behave?

San Joaquin pocket mice are active at night when they hunt, and spend the day underground in a burrow. Some of them will be searching for food above ground while others are inactive underground. They hibernate in phases during fall, winter, and spring, depending on how much energy they have. In the spring, they have a normal body temperature much more often than they do in winter. San Joaquin pocket mice sunbathe by digging in the ground with their forepaws, lowering their cheeks, and laying down. They switch back and forth between sides and choose their spot to sunbathe based on what others are doing. This means it may have started as a way to spread their scent. They also scent-mark on purpose. San Joaquin pocket mice can also be found gathering seeds, traveling, and making burrows or nests. ("Terrestrial Mammal Species of Special Concern in California", 1998; Best, 1993)

Home Range

Scientists haven't don't have much information about the home range of San Joaquin pocket mice.

How do they communicate with each other?

San Joaquin pocket mice communicate by growls, squawls, and low-pitched grunts. They also chatter their teeth and drum their feet. They also use scent marking and touching to communicate during mating. They have senses of sight, touch, hearing, and chemicals. (Best, 1993)

What do they eat?

San Joaquin pocket mice mostly eat seeds of grasses, shrubs, and other flowering plants. They also eat animals with soft bodies like insects, cutworms, earthworms, and even grasshoppers. In captivity, they eat parakeet seeds, rolled oats, sunflower seeds, and small amounts of leaves. They can be caught with seeds and oats. San Joaquin pocket mice 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

What eats them and how do they avoid being eaten?

San Joaquin pocket mice are eaten by birds of prey, foxes, snakes, and feral cats. They have the same color as the sandy soil around them, so they have good camouflage. They seek safety if they sense a predator and reduce their risk by being active at night. ("Terrestrial Mammal Species of Special Concern in California", 1998)

  • These animal colors help protect them
  • cryptic

What roles do they have in the ecosystem?

San Joaquin pocket mice are both predators and prey. They have lost a lot of their habitat, so scientists don't know much about how they relate to their ecosystems. They may disperse seeds and help aerate the soil when they burrow in the ground. ("Terrestrial Mammal Species of Special Concern in California", 1998)

Do they cause problems?

San Joaquin pocket mice aren't known to have any negative impacts on humans.

How do they interact with us?

San Joaquin pocket mice eat insects, which are pests to farmers.

Are they endangered?

San Joaquin pocket mice are listed as a species of least concern on the IUCN Red List. Although agricultural and urban development have led to habitat loss, degradation, and fragmentation, they are currently considered secure throughout much of their range. Most of the population decline has been in the northern part of the range. It is thought that up to 90% of the original habitat has been destroyed. Official threats include; agriculture, annual and perennial non-timber crops, and industrial farming and ranching. Rodenticides used to control ground squirrel populations also threaten San Joaquin pocket mice. ("Terrestrial Mammal Species of Special Concern in California", 1998; Linzey and Hammerson, 2009)

San Joaquin pocket mice are not endangered, even though up to 90% of their original habitat has been destroyed. Farming and building buildings have destroyed, damaged, and broken up their habitat. They are threatened by farming, ranching, and chemicals used to control numbers of ground squirrels. ("Terrestrial Mammal Species of Special Concern in California", 1998; Linzey and Hammerson, 2009)


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.


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 generate their own body heat through metabolic processes.

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.


animals that have little or no ability to regulate their body temperature, body temperatures fluctuate with the temperature of their environment, often referred to as 'cold-blooded'.


the state that some animals enter during winter in which bodily functions slow down, reducing their energy requirements so that they can live through a season with little food.


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 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

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

University of Michigan Museum of ZoologyNational Science Foundation

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LaMasters, J. 2012. "Perognathus inornatus" (On-line), Animal Diversity Web. Accessed April 23, 2014 at

BioKIDS is sponsored in part by the Interagency Education Research Initiative. It is a partnership of the University of Michigan School of Education, University of Michigan Museum of Zoology, and the Detroit Public Schools. This material is based upon work supported by the National Science Foundation under Grant DRL-0628151.
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