Fresno Kangaroo Rat

Dipodomys nitratoides exilis

Description

The Fresno kangaroo rat, Dipodomys nitratoides exilis, is one of the smallest of the several kangaroo rats of California, having a head and body length of about 10.5 in (27 cm). It is dark buff above and white below, with large, protruding eyes and very small front legs. The tail has a crest of longer hairs terminating in a tuft. It has darker facial markings than the other subspecies. It moves about by hopping, using its muscular hind legs much like a kangaroo.

Behavior

The species is nocturnal and feeds on seed grains and the leafy parts of plants, particularly wild oats, brome grasses, soft chess, wild barley, and fesque. It transports its food to underground caches in cheek pouches, which are formed from folds of fur-lined skin that stretch back as far as the neck. Kangaroo rats need very little water to survive and are thought to obtain their needs from dew and succulent plants. Kangaroo rats breed year round, but there are fewer births in the winter months. Gestation takes four to five weeks, after which up to five young are born; these leave the nest after about six weeks. One female can bear as many as three litters a year, but few individuals live long enough to breed more than once or twice. Breeding probably occurs in late fall or early winter at the beginning of the rainy season. Females may breed with more than one male during estrus. The young are born in the burrow in a nest constructed of dried, shredded vegetation.

Habitat

The Fresno kangaroo rat appears always to have been restricted to the native alkali sink-open grassland plant community of western Fresno County in areas with sufficient vegetation to provide food and cover.

Distribution

This kangaroo rat's original range probably covered an area of about 250,000 acres (101,200 hectares) in the San Joaquin Valley of central California, extending in the north to the San Joaquin River, in the east to the town of Fresno, in the south to the Kings River, and in the west to the Fresno Slough. Shortly after its discovery in 1891, the Fresno kangaroo rat began to decline because of agricultural encroachment into its habitat, and for many years it was thought to be extinct. However, in 1933 a population was rediscovered. A survey from 1938 indicated that about 100,000 acres (40,500 hectares) of habitat remained within the original range of the kangaroo rat, but by 1975 this habitat had declined to an estimated 15,000 acres (6,070 hectares). An aerial survey in November 1981 revealed that only 6,425 acres (2,600 hectares) of potentially suitable habitat remained, the rest having been converted for agriculture or residential development. Field studies in 1981-1982 found that only about 860 acres (348 hectares) of this land, mostly state-owned, was actually occupied by the Fresno kangaroo rat. Nearly all of the kangaroo rat's remaining potential habitat has suffered heavy grazing, and some will probably be converted to agricultural use in the near future.

Threats

The habitat requirements of the Fresno kangaroo rat seem even more restrictive than those of other kangaroo rats. This species builds extensive but shallow burrow systems and, therefore, requires land that is suitably compact to permit burrow construction. Dense vegetation is required to provide sufficient food and to enable escape from predators. This animal, unlike some other rodents, is not known to utilize cultivated areas. The drought in 1977 and competition with the Heermann's kangaroo rat (Dipodomys heermanni ) may be partly responsible for the Fresno kangaroo rat's decline.

Conservation and Recovery

Critical Habitat has been designated for the Fresno kangaroo rat to comprise 860 acres (348 hectares) in western Fresno County, California. This acreage is located generally to the south of the San Joaquin River, to the west of the town of Kerman, to the north of the Fresno Slough Bypass, and to the east of the Fresno Slough. Of this land, about 565 acres (229 hectares) are within the state Alkali Sink Ecological Reserve, 20 acres (8 hectares) are part of the state-owned Mendota Wildlife Management Area, and the remainder is privately owned.

Contacts

U. S. Fish and Wildlife Service
Sacramento Fish and Wildlife Office
Federal Building
2800 Cottage Way, Room W-2605
Sacramento, California 95825-1846
Telephone: (916) 414-6600
Fax: (916) 460-4619

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
Eastside Federal Building
911 N. E. 11th Ave.
Portland, Oregon 97232-4181
Telephone: (503) 231-6121
http://pacific.fws.gov/

References

Culbertson, A. E. 1934. "Rediscovery of Dipodomys nitratoides exilis. " Journal of Mammalogy 15:161-162.

Hoffman, M. W., and D. L. Chesemore. 1982. "Distribution and Status of the Fresno Kangaroo Rat, Dipodomys nitratoides exilis. " California Department of Fish and Game, Sacramento.

Koos, K. A. 1979. "The Fresno Kangaroo Rat Study,1979." California Department of Fish and Game, Sacramento.