California Mouse
Peromyscus californicus is found from San Francisco Bay south and east along the coast ranges and in the eastern Sierra Nevada from Mariposa Co. south to Kern Co. in California south to Bahia San Quintin on the Pacific coast of northwestern Baja California. Peromyscus californicus is generally restricted to dense chaparrel and broad-sclerophyll woodland. The limiting factor for its small geographic range may be the need for naturally occurring burrow holes of the proper size for these larger animals, as they are poor natural burrowers. The co-occurrence of woodrat houses and a distributional association with the California laurel complex have also been noted as potential limiting factors, although there is no direct evidence to implicate any of these.
California Mouse
Peromyscus californicus is the largest species in its genus. Its total length is between 220-285 mm, with tail length ranging from approximately 117-156 mm. It is distinctly bicolored. Adults have a yellowish brown or gray mixed with black dorsal coloring, and a white underside, and feet. Many individuals have a distinctly fulvous throat patch and a fulvous lateral line separating dorsal from ventral pelage in the shoulder region, sometimes extending to the thigh. Juveniles are gray on top with a white underside. The tail matches the dorsal pelage and is not sharply bicolored. The ears are large, ranging from 20-25 mm.
Reproduction
Mating may occur year round, but mainly from March to September. In the lab P. californicus can have up to 6 litters per year, but in the wild the average is 3-4 . Gestation is from 21-25 days and average litter size is 2, with a slight increase in litter size with the age of the female. Compared to other species of Peromyscus, P. californicus young are rather precocious, although weaning is not completed for about 5 weeks. They also have a long period before reaching sexual maturity, approximately 11 weeks for females and even longer for males.
Behavior
Peromyscus californicus is nocturnal, with a slight activity peak just before dawn. Usually a docile mouse, it will actively defend its nest from conspecifics of the same sex. A poor burrower, Peromyscus californicus readily uses woodrat (Neotoma fuscipes) houses for dens, and where found together, P. californicus actively excludes its conspecific P. truei from these woodrat houses. Unlike most mice P. californicus is truly monogamous, and once mated will stay paired for life. The male may help raise the young.
Food Habits
Peromyscus californicus specializes on the fruits, seeds and flowers of shrubs. In woodland habitat the seeds of California bay are the major food. Arthropods may make up a small percentage on the diet but these are not actively hunted. Water is most likely obtained from the food that it eats and supplimented with dew; P. californicus is not as good at water conservation as other species in the genus. In captivity they should be offered a complete diet of rodent lab blocks, and rat or mouse mix, with bits of fruit or veggies regularly. Cheerios or wheat bread are great treats, in small quantities. Do NOT feed chocolate, fried foods, salted foods, candy or junk food! They may enjoy crickets and mealworms if they are captive bred, never feed wild insects as they may carry parasites. Vitamins, like Nutri-Cal are a good addition to their diet, and added calcium during nursing and growth due to demands on their systems at those times, but take care not to overdo it. Water bottles should be used to proved constant, clean water. Ceramic or stoneware food dishes work well for keeping seeds or fresh foods off the floor, and a wire mesh hopper that allows them to eat the lab blocks through without extra waste.
