PACIFIC POCKET MOUSE } Perognathus longimembris pacificus
HABITAT: This mouse lives on fine-grain, sandy substrates and historically inhabited coastal dunes, river alluvium, and sage scrub habitats growing on marine terraces within approximately 2.4 miles of the ocean.
RANGE: The Pacific pocket mouse is endemic to coastal southwestern California; the mouse formerly occurred at a minimum of eight locales encompassing 29 sites from Los Angeles County south to San Diego County.
MIGRATION: The Pacific pocket mouse is nonmigratory.
BREEDING: Breeding season generally peaks in spring but varies with temperatures, food supply, and plant growth. Females typically produce one or occasionally two litters per year, with two to eight young per litter. Gestation takes 22 to 23 days; young are weaned in 30 days. The Pacific pocket mouse reaches sexual maturity in two to five months, though reproduction may not take place in years with below-average precipitation.
LIFE CYCLE: Young are born in a nest in an underground burrow and are capable of breeding in the same season they’re born. In captivity, Pacific pocket mice may live four to six years; in the wild, mice may live one to two years. Adults may hibernate from roughly September to April and stay in their burrows continuously for up to five months in winter, alternating between periods of dormancy and feeding on stored seeds. A low food supply likely induces winter hibernation behavior; during winters of abundant food, mice will remain active.
FEEDING: Mice feed primarily on seeds of grasses and forbs, as well as on green vegetation in spring and sometimes on insects. The Pacific pocket mouse stores food in underground burrows.
THREATS: The pocket mouse faces severe and continuing loss of habitat to urban and agricultural use; remaining mouse populations are imminently threatened by land development, fuel modification for fire protection, and domestic- and feral-cat predation.
POPULATION TREND: The population of the Pacific pocket mouse has declined markedly from severe and continuing loss of habitat due to urban and agricultural expansion. NatureServe notes that the “remaining population consists of a few dozen individuals.”