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short-nosed kangaroo rat
Dipodomys nitratoides brevinasus

Status

U.S.A. Species of Concern

Life History

The short-nosed kangaroo rat, Dipodomys nitratoides brevinasus, is one of three subspecies of the San Joaquin kangaroo rat. The appearance of the short-nosed subspecies is similar to the Fresno and Tipton kangaroo rats. The short-nosed kangaroo rat is nocturnal and active year-round. The foraging behavior and diet of the short-nosed kangaroo rat is the same as those of the other subspecies of the San Joaquin kangaroo rat.

At higher elevations in the western portion of its geographic range, the reproductive season of the short-nosed kangaroo rat is about 2 to 3 months shorter than on the Valley floor, with breeding beginning in late February or March and typically ending by May. In years with a prolonged wet spring, individuals may continue breeding through August. In captive-bred individuals, the gestation period lasted 32 days and the average litter size was 2.3. In the wild, most females appear to have one litter per year and the young females (born in the same year) appear to reproduce only when there is a prolonged wet season. Similar to the other subspecies of the San Joaquin kangaroo rat, the populations of the short-nosed kangaroo rat undergo dramatic population fluctuations.

Typically, short-nosed kangaroo rats inhabit grasslands with scattered shrubs and desert-shrub associations on powdery soils. They inhabit highly saline soils around Soda Lake on the Carrizo Plain, and less saline soils elsewhere. In the Panoche Valley, San Benito County, this species is found on gently sloping and rolling, low hill-tops that have some shrubs. Over most of their range, they are generally more numerous in lighter, powdery soils such as the sandy bottoms and banks of arroyos and other sandy areas.

The extensive agricultural development of the 1960's and 1970's within its historic range is the main cause of the decline of the short-nosed kangaroo rat. Loss of the best habitats and the large populations they supported, together with habitat fragmentation and the resulting isolation of the populations and population fluctuations, have apparently caused their extirpation from some undeveloped sites. In limited areas, widespread use of rodenticides to control ground squirrels may have contributed to extirpation of some populations. Because the distribution and population statuses are not well-understood, present or potential threats to this species cannot be adequately assessed.

Distribution

There has not been a comprehensive study defining the historical distribution of the short-nosed kangaroo rat. Museum and literature records, and recent studies at a few sites have provided only partial information of the historic range of this species. They occupied arid grassland and shrubland associations along the western half of the Valley floor and hills on the western edge of the Valley floor from the Los Banos area, Merced County, south to the foothills of the Tehachapi Range and extending east and northward inland above the edges of the Valley floor to near Poso Creek, north of Bakersfield. They also occurred on the Carrizo Plain and the upper Cuyama Valley.

The extent of its current distribution is also unknown. Some trapping surveys have shown that small, fragmented and widely scattered populations still exist within some of the known historic range. Populations are known from the Coalinga area, Fresno County, a few scattered locations in the Kettlemen and Lost Hills, Kings and Kern counties, the Lokern, Elk Hills, San Emigdio, and Wheeler Ridge regions of western Kern County, the Carrizo Plain Natural Area, and the Caliente Mountains at the edge of the Cuyama Valley.

Classification

Order RODENTIA, Family HETEROMYIDAE, Genus Dipodomys, Species nitratoides.

Subspecies

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

Recent Synonyms

None.

Other Common Names

None.

References

Hoffmann, W.M. 1975. Geographic variation and taxonomy of Dipodomys nitratoides from the California San Joaquin Valley. M.A. thesis, California State Univ., Fresno, 75 pp.; 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. Williams, S. Byrne, and T.A. Rado, eds.). The California Energy Commission, Sacramento, 386 pp.

Size

Total length
males: 238-252 mm (9.37-9.92 in)
females: 232-246 mm (9.13-9.69 in)

Weight (range for both sexes)
39-44 g ( 1.26-1.55 oz)

Length of hind foot (mean)
males: 35.7 mm (1.41 in)
females: 34.5 mm (1.36 in)

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 short-nosed kangaroo rat is the largest of all the 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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