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Fresno kangaroo rat
Dipodomys nitratoides exilis

Status

U.S.A. and California Endangered

Life History

Like all kangaroo rats, the Fresno kangaroo rat is adapted for survival in an arid environment. Kangaroo rats move about by bipedal (two-footed) hopping, using their elongated hind limbs, and a long tufted tail for balance. Their forelimbs are shorter with strong claws that facilitate digging burrows. Other characteristics include a larger head compared to typical rodents; large, dorsally placed eyes; and small rounded ears. The fur is a tawny yellow on the head and back, and white on the belly. A white stripe extends across the hips and continues down the sides of the tail, which is blackish on the top and the bottom.

Fresno kangaroo rats collect and carry seeds in fur-lined external cheek pouches. Their diet consists primarily of seeds, but they may also eat some types of green herbaceous vegetation and insects. Most kangaroo rats gather seeds when they are available and cache (store) them for consumption later. Typically, caches are made in small pits on the surface of the soil, scattered over the home range of the individual. The small caches hold only the contents of two cheek pouches.

Breeding is probably initiated in winter after onset of the rainy season. Nothing is known about pair bonds in wild populations, but it is thought that there are no lasting male-female pair bonds formed. In captivity, gestation is 32 days and the average litter size is 2. Young are born in the burrow where they remain until they are fully furred and able to move about easily.

Fresno kangaroo rats shelter in ground burrows that are dug by them or their predecessors. Burrows are usually found in relatively light, sandy soils in raised areas. There are usually two to five burrow entrances that slant gently underground, and one or more holes that open from a vertical shaft.

Within the alkali-sink plant associations, Fresno kangaroo rats were probably the most numerous small mammal under natural conditions. As such, they provided a major source of food for a variety of predators, including the endangered San Joaquin kit fox. Their burrows were used extensively by the endangered blunt-nosed leopard lizard and other reptiles. Their seed-caching behavior may have been important in the dispersal and germination of some plants, and their burrowing and digging probably beneficially affected soil structure and fertility.

Distribution

The known historical geographic range of the Fresno kangaroo rat encompassed an area of grassland and alkali desert scrub communities on the San Joaquin Valley floor in Merced, Kings, Fresno, and Madera counties. Recently they have been found only in alkali sink communities from 200 to 300 feet in elevation. Currently there are no known populations within its historical geographic range in Merced, Madera, and Fresno counties. The last record of a Fresno kangaroo rat in Fresno County was in 1992 at the Alkali Sink Ecological Reserve. In 1975, populations of San Joaquin kangaroo rats (D. nitratoides) occurred on the Mendota Wildlife Area, Fresno County, and currently occur on Lemoore Naval Air Station, Kings county, but the subspecies classification of these populations is uncertain (either D. n. exilis or D. n. brevinasus).

The Fresno kangaroo rat was believed to be extinct by the early 1900's, only to be rediscovered in 1933. By 1974, known habitat for these animals had been reduced and fragmented primarily by agricultural developments, urbanization, and transportation infrastructures.

Existing threats to this species' survival include flooding of existing habitat in Fresno County which is located near the San Joaquin River. The most recent extensive floods were in 1986 and 1997. Loss of habitat to cultivation, year-round grazing and conversion of land to other uses continue to diminish the size and quality of existing, historical habitat. Other potential threats are the indiscriminate use of rodenticides, competition with Heermann's kangaroo rats (Dipodomys heermanni), and disease and depredation, any of which could decimate small, isolated populations.

Classification

Order RODENTIA, Suborder SCIUROGNATHI, Family HETEROMYIDAE, Genus Dipodomys, Species nitratoides

Subspecies

D. n. exilis, Fresno kangaroo rat, is one of the three subspecies of the San Joaquin kangaroo rat. The other two subspecies include: D. n. nitratoides, Tipton kangaroo rat, and D. n. brevinasus, Short-nosed kangaroo rat.

Recent Synonyms

None.

Other Common Names

None.

References

Chesemore, D. L. and W. M. Rhodehamel. 1992. Ecology of a vanishing subspecies: the Fresno kangaroo rat (Dipodomys nitratoides exilis). Pp. 99-103, in Endangered and sensitive species of the San Joaquin Valley, California: their biology, management, and conservation (D.F. Willliams, S. Byrne, and T.A. Rado, eds.); Grinnell, J. 1922. A geographic study of the kangaroo rats of California. Univ. of California Publ. Zool., 24:1-124; Hoffmann, W. M. 1974. The Fresno kangaroo rat study. Calif. Dept. Fish and Game, Final report, Job II-5.4, 19pp.; Hoffmann, W. M. 1975. Geographic variation and taxonomy of Dipodomys nitratoides from the California San Joaquin Valley. M.A. thesis, California State Univ., Fresno, 75pp.; Williams, D. F. and D. Germano. 1992. Recovery of endangered kangaroo rats in the San Joaquin Valley, California. Trans. West. Sect. Wildl. Soc. 28:93-106.; Williams, D. F. and K. S. Kilburn. 1992. The conservation and status of the endemic mammals of the San Joaquin faunal region, California. Pp. 329-345, in Endangered and sensitive species of the San Joaquin Valley, California: their biology, management, and conservation (D.F. Willliams, S. Byrne, and T.A. Rado, eds.).

Size

Total length (average):
231 mm (males)
225 mm (females)
Length of hind foot (average):
33.9 mm (males)
33.4 mm (females)
Weight:
30-50 g (range for sexes combined)

Identification

The San Joaquin kangaroo rat can be distinguished from other kangaroo rats within its geographic range by the presence of four toes on its hind foot; the other species in the area have five toes. The Fresno kangaroo rat is the smallest of the three subspecies of D. nitratoides. Individuals of the three subspecies cannot be reliably distinguished without dissection unless the geographic location of the individual is known.

Authors of Profile

N.L. Brown and D.F. Williams

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