Perognathus inornatus
San Joaquin pocket mouse

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)

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)

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)

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)

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)

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

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)

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)

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)

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)

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

There are no adverse effects of P. inornatus on humans.

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)