Field Guide to Mammals
of Southern California
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San Bernardino Kangaroo Rat (Dipodomys merriami parvus)
Extant populations and potential habitat for San Bernardino kangaroo rat occur in several locations at the base of the San Bernardino and San Jacinto Mountains. A large population along the Santa Ana River extends upstream to Greenspot Road bridge, which is less than 1 mile (1.6 kilometers) below the San Bernardino National Forest boundary (U.S. Fish and Wildlife Service 1998). A second population occurs in Bautista Canyon. The population in Cajon Wash is known to extend at least to the national forest boundary and may occur on National Forest System lands in Lytle Creek (Loe pers. comm.).
San Bernardino kangaroo rat is one of 19 subspecies of Merriam's kangaroo rat (Dipodomys merriami). San Bernardino kangaroo rat is distinguished from the other southern California subspecies by its darker body fur, smaller size and occurrence of four toes on its hind feet. This subspecies is one of the most highly differentiated of Merriam's kangaroo rats, possibly because of its complete geographic isolation from the other subspecies (U.S. Fish and Wildlife Service 2001).
San Bernardino kangaroo rats are found primarily on sandy loam substrates, characteristic of alluvial fans and floodplains, where they are able to dig shallow burrows (U.S. Fish and Wildlife Service 1998). They are always associated with alluvial fans. San Bernardino kangaroo rats can be found in all phases of alluvial fan sage scrub, as well as coastal sage scrub and even chaparral habitats within the species historical range. Soil texture plays an important role in habitat preference. Like other kangaroo rats, the San Bernardino kangaroo rat avoids rocky soils (Brown and Harney 1993, Loe pers. comm., U.S. Fish and Wildlife Service 1998). The San Bernardino kangaroo rat reaches its highest densities in early and intermediate seral stages (McKernan 1997). Early successional habitat provides the relatively open vegetation structure preferred by this subspecies.
The breeding season of Merriam's kangaroo rat lasts from mid-winter until spring depending on environmental conditions. In years with heavy winter rains and abundant herbaceous annuals, breeding activities may increase. Gestation is 33 days, and litter size averages 2.4 young (Daly and others 1984). Weaning occurs 24–33 days after birth (Chew and Butterworth 1964). In favorable years, females are capable of breeding shortly after weaning. They may breed twice in one year if conditions allow. Herbaceous material or free water is believed to be necessary for successful reproduction (Soholt 1973).
Like other kangaroo rats, San Bernardino kangaroo rat is primarily nocturnal. It exhibits crepuscular activity, emerging from burrows at dusk to forage and returning to the day burrow before dawn. Individuals reduce surface activity in areas with less vegetation cover and on nights with high levels of moonlight (Behrends and others 1986a, Daly and others 1992a).
Diet and Foraging
San Bernardino kangaroo rat diet primarily consists of seeds, herbaceous material and insects, when available. D. merriami collects seeds in cheek pouches and stores them in scattered surface caches in the vicinity of home burrows (Daly and others 1992b). Green vegetation and insects are also important seasonal food sources. Insects, when available, have been documented to constitute as much as 50 percent of a kangaroo rat's diet (Reichman and Price 1993). San Bernardino kangaroo rats are known for their ability to live indefinitely without water on a diet consisting entirely of dry seeds (Reichman and Price 1993).
Merriam's kangaroo rat home ranges average 0.8 acre (0.32 hectare). Individuals tend to establish home ranges close to their natal home range. Outlying areas of home ranges may overlap, but core areas are defended territories (U.S. Fish and Wildlife Service 1998). Population densities of Merriam's kangaroo rat fluctuate, probably in association with resource availability. Zeng and Brown (1987) recorded population densities of 1 to 8 individuals/acre (2–18 individuals/hectare) in the Chihuahuan Desert in southeastern Arizona. Chew and Butterworth (1964) reported densities of 0.12 to 1.5/acre (0.3–3.7/hectare) in creosote scrub habitats in the Mojave Desert. Christopher (1973) found a density of 7.4/acre (18.5/hectare) in creosote scrub on the western edge of the Colorado Desert, and 1.0/acre (2.6/hectare) in nearby pinyon-juniper communities. Soholt (1973) found densities of 5.2/acre (13/hectare) in early spring and 7.6/acre (19/hectare) in fall in a creosote scrub population.
Miller and Stebbins (1964) recorded that kit foxes and badgers preyed on this species. Daly and others (1990) found that coyotes, snakes, owls and shrikes were also predators. The expansion of urban areas has increased the level of predation by urban associated animals such as domestic cats. Predation by cats has been documented for the San Bernardino kangaroo rat (McKernan pers. comm.).
Behrends, P.; Daly, M.; Wilson, M.I. 1986a. Aboveground activity of Merriam's kangaroo rats (Dipodomys merriami) in relation to sex and reproduction. Behaviour 96: 210-226.
Brown, J.H.; Harney, B.A. 1993. Population and community ecology of heteromyid rodents in temperate habitats. In: Genoways, H.H.; Brown, J.H., eds. Biology of the Heteromyidae. Special Publication No. 10 of the American Society of Mammalogists.
Carter, K.J.; Braden, G.T. 2003. Survey results for the San Bernardino Kangaroo Rat (Dipodomys merriami parvus) in the San Bernardino National Forest (Lytle Creek, Cajon Creek, Bautista Canyon), with supplemental survey results for areas adjacent to the San Bernardino National Forest.
Christopher, E.A. 1973. Sympatric relationships of the kangaroo rats, Dipodomys merriami and Dipodomys agilis. Journal of Mammalogy 54: 317-326.
Chew, R.M.; Butterworth, B.B. 1964. Ecology of rodents in Indian Cove (Mojave Desert), Joshua Tree National Monument, California. Journal of Mammalogy 45: 203-225.
Daly, M.; Wilson, M.I.; Behrends, P. 1984. Breeding of captive kangaroo rats, Dipodomys merriami and D. microps. Journal of Mammalogy 65: 338-341.
Daly, M.; Wilson, M.; Behrends, P.R.; Jacobs, L.F. 1990. Characteristics of kangaroo rats, Dipodomys merriami, associated with differential predation risk. Animal Behavior 40: 380-389.
Daly, M.; Behrends, P.R.; Wilson, M.I.; Jacobs, L.F. 1992a. Behavioral modulation of predation risk: Moonlight avoidance and crepuscular compensation in a nocturnal desert rodent, Dipodomys merriami. Animal Behaviour 44: 1-9.
Daly, M.; Jacobs, L.F.; Wilson, M.I.; Behrends, P.R. 1992b. Scatter-hoarding by kangaroo rats (Dipodomys merriami) and pilferage from their caches. Behavioral Ecology 3: 102-111.
Jones, W.T. 1989. Dispersal distance and the range of nightly movements in Merriam's kangaroo rats. Journal of Mammalogy 70: 27-34.
McKernan, R.L. 1997. The status and known distribution of the San Bernardino kangaroo rat (Dipodomys merriami parvus): Field surveys conducted between 1987 and 1996. Unpublished report on file at the U.S. Fish and Wildlife Service, Carlsbad, CA.
Miller, A.H.; Stebbins, R.C. 1964. The lives of desert animals in Joshua Tree National Monument. Berkeley, CA: University of California Press.
Soholt, L.F. 1973. Consumption of herbaceous vegetation and water during reproduction and development of Merriam's kangaroo rat, Dipodomys merriami. American Midland Naturalist 98: 445- 457.
U.S. Fish and Wildlife Service. 1998. Endangered and threatened wildlife and plants; Final rule to list the San Bernardino kangaroo rat as endangered. 63 Federal Register 185 51005-51017, September 24, 1998.
U.S. Fish and Wildlife Service. 2001. Biological and conference opinions on the continued implementation of land and resource management plans for the four southern California National Forests, as modified by new interim management direction and conservation measures (1-6-00-F-773.2).
Zeng, Z.; Brown, J.H. 1987. Population ecology of a desert rodent: Dipodomys merriami in the Chihuahuan Desert. Ecology 68: 1328-1340.
Information gathered from California DFG - California Interagency Wildlife Task Group