San Diego Management & Monitoring Program


Northwestern San Diego pocket mouse
Chaetodipus fallax fallax

Vertebrata
Castorimorpha

Vertebrata Castorimorpha
Kingdom Phylum Subphylum Class Order Suborder Family

Current distribution rangewide

Restricted to the central and northern Baja California Peninsula and southwestern California [1]. Range is widespread in the valleys of western Riverside and southwestern San Bernardino counties extending northwest to the vicinity of Claremont in Los Angeles County [2;3; both cited in 4]. Also found throughout western Baja California south to extreme northwestern Baja California Sur [2;5; both cited in 4]. Elevational range is from sea level to 1350 m (4500 ft) (Santa Rosa mountains, Riverside county) and 1800 m (6000 ft) (Cactus Flat, north slope of San Bernardino mountains) [6].


Known Populations in San Diego County

Within the MSPA, occurrences have been found in MU 1 (Sunset Cliffs), MU 3 (Crestridge), MU 4 (Mission Trails Regional Park, Sycamore Canyon and Goodan Ranch, Cleveland national Forest), MU 7 (TorreyPines), MU 6 (Elfin Forest Recreational Reserve, Santa Fe Valley), and MU 11 (Cleveland National Forest).


List status

SSC


Habitat affinities

Common resident of sandy herbaceous areas, usually in association with rocks or coarse gravel [7;8; both cited in 6] in southwestern California. Occurs mainly in arid coastal and desert borders [6]. Habitats tend to be stony soils above sandy desert fans and rocky areas within shrub communities such as coastal sage scrub, chamise-redshank chaparral, mixed chaparral, sagebrush, desert wash, desert scrub, desert succulent scrub, pinyon-juniper, and annual grassland [9, cited in 1;6].


Taxonomy and genetics

C. fallax has 6 recognized species [10] with two subspecies found in southern California: C. f. fallax from southern California through the coastal sage zone into the northern part of the Baja California Peninsula and C.f. pallidus in the eastern San Bernardino Mountains in California [1;4;10]. Formerly recognized as a subgenus of Perognathus before elevated to full generic stature 11, cited in 12].


Seasonal activity

Nocturnal [6;13]. Solitary [13]. Active year-round [6] though avoids high daytime temperatures in its burrows [8, cited in 6].


Life history/ reproduction

Breeding occurs chiefly from March to May [14]. Females can produce 1-3 litters per year [15, cited in 13]. An average of 4 young comprise a litter. Gestation is around 24-26 days [14]. Young become sexually mature at 5 to 6 months of age. Typical longevity in nature is only 4-6 months, but it is not unusual for some individuals to survive 1-2 years [15, cited in 13].


Diet and foraging

Forages on seeds of forbs, grasses, shrubs with a low to moderate preference for forb and shrub seeds, and a high preference for grass seeds [16]. Seeds transported within cheek pouches where it is stored in and around its burrow. May feed on some insects. Water obtained metabolically [6].


Dispersal

Home range varied from 0.19 to 0.45 ha, averaging 0.3 ha [17, cited in 10] No difference between sexes in home range size, and little overlap between sexes in home ranges, possibly the result of territoriality [10]. Territory probably the same size as home range [6].


Threats

Threatened by habitat fragmentation and loss due to development [13].


Northwestern San Diego pocket mouse sources