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Peromyscus Genetic Stock Center

Peromyscus californicus California mouse

*Information adapted from Mammalian Species, No. 85, The American Society of Mammalogists.


Peromyscus californicus is the largest species of the genus in the United States. P. californicus is restricted to central and southern California.


Pelage: Long and lax. Color varies; upper mixed with black; sides much paler; under creamy white, except base of tail which is russet; tail bicolored not sharply contrasted; manus and feet white (Osgood, 1909).

Size: Overall very large, with very large ears, tail longer than head and body (Osgood, 1909).

Weight: Ranges from 33.2 to 54.4 g (Allen, 1896; Grinnell and Orr, 1934; Burt and Grossenheider, 1964; Ingles, 1965).

Measurements: Total length is 220 to 285 mm; length of tail, 117 to 156; hind foot, 24 to 31; ear from notch, 20 to 27; greatest length of skull, 28.1 to 32.1; basilar length, 21 to 25.8; zygomatic width, 13.5 to 16.2; interorbital constriction, 4.3 to 5.1; length of nasals, 10.2 to 12.4; shelf of bony palate, 3.9 to 5.1; length of palatine slits, 5.3 to 6.9; diastema, 7 to 8.4; postpalatal length, 10.2 to 12.6; and length of maxillary toothrow, 4 to 5.1 mm. External and cranial dimensions increase in a stepped cline from 30°29' N to 38° N latitude (Grinnell and Orr, 1934).

*All measurements and descriptions refer to adult specimens unless otherwise stated.

Dorsal, ventral, and lateral views of skull, and lateral view of lower jaw of Peromyscus californicus insignis, CU 9393, female, from Pasadena, California.  Collected by J. Grinnell, 1904.  From Mammalian Species, No. 85.


Total length is 220 to 285 mm; tail is longer than head and body, commonly indistinctly bicolored, and well haired, but the annulations are not thoroughly concealed. Color is geographically variable, generally blackish brown above, sides ochraceous-tawny, venter pale olive-gray to buffy-brown (Osgood, 1909). Pelage is long and lax. For photographs and additional information, see Bond (1942), Eisenberg (1962), and Ingles (1965). 

The skull is large and the braincase well-inflated; tympanic bullae are large and inflated (figure 1). Molars are robust, no accessory cusps are on Ml; upper molars typically lack both lophs and styles, whereas lower molars may possess these structures; well developed ectostylid is often present, and low ectolophid on ml; occasional subspecific variation of lophs and styles was reported by Hooper (1957:19). Dental formula is i 1/1, c 0/0, p 0/0, m 3/3, total 16.

Baculum is vase shaped; its base is broad, flat, widest near middle, and has distal and proximal depressions; its shaft is relatively thick and has no protrusible tip; bacular length is 12.6 to 15.4 mm, mean 13.7 mm; width of base is 1.7 to 2.7 mm, mean 2.0 mm (Burt, 1960:51; for other details, description, and illustrations also see Blair, 1942:199 and Hooper, 1958:17). Ceratohyals are short, rectangular, and lacking terminal processes; unique among Peromyscus, but resembling Reithrodontomys megalotis (Sprague, 1941:305). 


P. californicus is restricted to California, occurring from San Francisco Bay southward along the coastal ranges as far as San Quintin, Baja California. It also occupies lower western slopes of the southern Sierra Nevada, from northwestern Mariposa County southward to Kern County, California. Altitudinal range is from sea level to 2440 m (8000 feet) Grinnell and Swarth, 1913:344; Grinnell and Orr, 1934; Hall and Kelson, 1959.



P. californicus has been reported from chaparral and oak woodland near Berkeley (McCabe and Blanchard, 1950; Cook, 1959; Marten, 1970, 1972, 1973), mesic laurel and redwood forests of the Santa Cruz Mountains (Streator, 1931; Rudd, 1948; Merritt, 1974), and chaparral of Monterey County (Linsdale and Tevis, 1951) and the Sierra Nevada foothills (Lawrence, 1966). It also occurs in chaparral and coastal sage scrub communities of southern California (Vaughan, 1954; Murray, 1957a; MacMillen, 1964; M'Closkey, 1970, 1972; Meserve, 1972, 1974), and was trapped in coniferous woodland and chaparral situations by Pequegnat (1951) and Ryan (1968). At its southern limit in Baja California, it is found on brush covered slopes (Huey, 1964).


A home range of 0.15 ha (0.37 ac) was determined by MacMillen (1964). The vertical component in spatial distribution is also a factor for home ranges of the California mouse (Meserve, 1977). Meserve (1972) found considerable arboreal behavior, primarily on three shrubs in the coastal sage scrub community.

The California mouse is often found inhabiting the abandoned dens of Neotoma.  Ecologists have studied water relations, food requirements, and relationships of P. californicus to the dens of N. fuscipes to elucidate habitat requirements of this mouse. Population estimates coupled with data on habitat preference for moist situations (Merritt, 1974; Meserve, 1974) and critical nutritional and shelter requirements have partially delimited the range of tolerance of the California mouse.


The California mouse is generally slow and passive with a decreased tendency to bite. In addition, it has long, dense, fine fur effective against cold, but ineffective in shedding water. Live-trapping studies of McCabe and Blanchard (1950) and Merritt (unpublished data) have found P. californicus to be completely soaked which resulted in high trap mortality.

P. californicus is a good climber, categorized as semiarboreal by Clark (1936). King et al. (1968) indicated that it is advanced in gnawing ability, but McCabe and Blanchard (1950:20) reported that it could enlarge holes or cracks in hollow logs, but was unable to start a hole in solid material. King et al. (1968) found it to be an inept digger and it has never been observed entering holes in the ground.

The nest of P. californicus is complex, commonly found under debris such as fallen logs. Nests are composed of coarse dry grasses, weeds and sticks and may ``consist of masses up to a bushel in bulk, though usually of less than half that size . . ." (McCabe and Blanchard, 1950:22). The center is a chamber lined with fine grasses. The nest is defended actively and is occupied for prolonged periods of time. Caching behavior was observed by Streator (1931).

Eisenberg (1962, 1963) combined his laboratory data with field and laboratory data from Svihla (1932) and McCabe and Blanchard (1950) to provide a picture of the social organization of P. californicus. Males are aggressive toward one another, and employ a unique fighting technique characterized by much jumping and avoidance, accompanied by a mewing cry thought to inhibit aggressive behavior of another individual. Peromyscus californicus is more strongly territorial than P. maniculatus and both males and females defend the nest site. Eisenberg (1963) showed that females of P. californicus exhibit a pronounced nest site attachment and defense, but other agonistic behavior was confined to males

The California mouse feeds on shrub fruits, seeds, and flowers (Meserve, 1972). A large portion of the diet constituted Rhus integrifolia, Lotus scoparius, and Salva apiana during months of availability. Other foods found periodically were grasses, forbs, fungi, and arthropods. Merritt (1974:108) showed that seeds of California laurel constituted a principal staple in the diet of P. c. parasiticus. Other important food items were unidentified leaf fragments, fungi, endosperm, and smaller quantities of berries, arthropods, and herbaceous stems.

P. californicus is active periodically through the night, a short burst of activity may occur shortly before dawn (Marten, 1970, 1972, 1973).

McCabe and Blanchard (1950), Eisenberg (1962), and Dudley (1973) found the California mouse lives in pairs in nature, even during parturition and lactation. Male and female were observed spending equal amounts of time with pups (Dudley, 1973, 1974x, 1974b).  Califoria mouse is also known to be monogamous (Ribble, 19 ;Gubernick, 19

Litter size means range from 1.87 to 2.5 young per litter (Svihla, 1932; McCabe and Blanchard, 1950; Rood, 1966; Drickamer and Vestal, 1973; MacMillen, 1964). Litters per year range from 2 to 6 (Svihla, 1932:31; McCabe and Blanchard, 1950). The gestation period for laboratory stock of P. californicus ranges from 21 to 25 days (Svihla, 1932).

Lactation is prolonged. Young weaned at about 5 to 6 weeks (Svihla, 1932; McCabe and Blanchard, 1950). The growth curve is similar to that of other species of Peromyscus, but weights are 40% greater (Layne, 1968:221). Sexual development is slow; females first show slightly perforate vulva at week 11 (McCabe and Blanchard, 1950).

Weasels and Barn owls are the main predators (Vestal, 1937; Von Bloeker, 1937).


P. californicus has a diploid chromosome number of 48. Hsu and Arrighi (1968:422) described them as "pairs A1, A2, B1 and B2, and 19 pairs of acrocentrics". The X chromosome is sub-metacentric and the Y chromosome is about the same length as the X but the centromere is more medially located.


Order Rodentia, Suborder Myomorpha, Family Muridae, Subfamily Sigmodontinae, Tribe Peromyscini, Genus Peromyscus, Subgenus Haplomylomys californicus-species group


P. c. parasiticus (Baird, ex Cooper, MS, 1858:478.). Type locality Santa Clara Valley, Santa Clara Co., California.

P. c. californicus (Gambel, 1848:78). Type locality Monterey County, California.

P. c. benitoensis (Grinnell and Orr, 1934:216). Type locality near Cook Post Office, 1300 feet, Bear Valley, San Benito Co., California.

P. c. mariposae (Grinnell and Orr, 1934:217). Type locality El Portal, 2500 feet, Mariposa Co., California.

P. c. insignis (Rhoads, 1895:33). Type locality Dulzura, San Diego Co., California.


Mus californicus Gambel, 1848:78. Type locality Monterey, California.

Peromyscus californicus, Thomas, 1894:364, first use of current name combination.


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Bond, RM. 1942. Food of the burrowing owl in western Nevada.. Condor. 44:183.

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Clark, FH. 1936. Geotropic behavior on a sloping plane of arboreal and non- arboreal races of mice of the genus Peromyscus. Journal of Mammalogy. 17:44-47.

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