|Scientific Name:||Dipodomys ingens (Merriam, 1904)|
|Red List Category & Criteria:||Endangered B1ab(i,ii,iii) ver 3.1|
|Assessor(s):||Linzey, A.V. & NatureServe (Williams, D.F. & Hammerson, G.)|
|Reviewer(s):||Amori, G. (Small Nonvolant Mammal Red List Authority) & Chanson, J. (Global Mammal Assessment Team)|
Listed as Endangered because its extent of occurrence is less than 5,000 km2, its range is severely fragmented, and there is an ongoing decline in the extent of occurrence, area of occupancy, and extent and quality of the species' habitat.
|Previously published Red List assessments:|
|Range Description:||The species' range is endemic to California in the United States and is confined to a narrow strip along the southwestern border of the San Joaquin Valley and a few nearby valleys to the west, including the Carrizo and Elkhorn plains and upper Cuyama Valley, with scattered colonies in the Ciervo, Kettleman, Panoche, and Turney Hills, and the Panoche Valley (Grinnell 1922, Hall 1981, Williams and Kilburn 1991, Williams et al. 1993). Its historical range extended from Merced County south to the base of the Tehachapi Mountain in Kern County, and west to eastern San Luis Obispo County and extreme northern Santa Barbara County (Williams et al. 1993). Its elevational range extends to about 868 m asl (400-2,850 feet).|
The population is currently fragmented into six major geographic units: 1) the Panoche region in western Fresno and eastern San Benito counties; 2) Kettleman Hills in Kings County; 3) San Juan Creek Valley in San Luis Obispo County; 4) western Kern County in the area of the Lokern, Elk Hills, and other uplands around McKittrick, Taft, and Maricopa; 5) Carrizo Plain in eastern San Luis Obispo County; and 6) Cuyama Valley in Santa Barbara and San Luis Obispo counties (see USFWS 1998). These major units are fragmented into more than 100 smaller populations, many of which are isolated by several miles of barriers such as steep terrain with plant communities unsuitable as habitat, or agricultural, industrial, or urban land without habitat for this species (USFWS 1998).
Native:United States (California)
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||The huge colonies of this species described in historical literature no longer exist. Extant habitat comprises only about 1.8 percent of the historical habitat (Williams 1992, USFWS 1998).The extant distribution includes more than 100 more or less distinct populations, but most of these represent fragments of a formerly more continuous distribution. There are six major geographic units, each of which could be regarded as a single occurrence or subpopulation. Total adult population size is unknown but probably exceeds 100,000 during average conditions. Adult population size varies substantially with drought and plant productivity (USFWS 1998); density ranges from one to 110 individuals per hectare (see USFWS 1998).|
Within the area of currently occupied habitat, populations have expanded and declined with changing weather patterns since 1979; at their peak in 1992 to 1993, there probably were about six to 10 times more individuals than at their low point in spring of 1991, when a majority of the 11,145 hectares probably was uninhabited and most of the rest was inhabited by less than 10 percent of peak numbers (see USFWS 1998 for sources). Population density is five to 50 per hectare (18-69/ha in the larger and denser colonies; Williams and Kilburn 1991). Extant population sizes are small; from fewer than 10 to several hundred individuals (Braun 1985).
|Current Population Trend:||Decreasing|
|Habitat and Ecology:||The habitat of giant kangaroo rats consists of gently sloping and level piedmont plains and (formerly) areas supporting saltbush and perennial grasses; habitat now is dominated by introduced annuals, with many shrubs in some areas. The species occupies areas of sparse vegetative cover and well-drained soils and slope generally less than 9% (Williams and Kilburn 1991) (sometimes up to 22%; USFWS 1998), often in areas that are heavily grazed by cattle and sheep (Williams and Kilburn 1991). They prefer semi-arid slopes at the head of draws in barren shrubless areas, with loose, easily diggable, sandy loam soils. Found in underground burrows when inactive. They are absent from areas continuously in dry-land cultivation and from irrigated fields but may recolonize fallow dry-land grain fields if there are colonies on uncultivated land nearby (Williams and Kilburn 1991). Habitats listed in order of decreasing favorability: 1) annual grassland association in areas with less than five to six inches annual rain, and level to gently sloping ground, 2) alkali desert scrub association in areas with less than five to six inches annual rain, sandy loam soils, and level to gently sloping ground, 3) friable soils of sand, loam, clay loam or gravelly in areas with the above characteristics, and 4) slopes of 10-15 degrees with the above characteristics and located near colonies in more favorable habitats (D. Williams pers. comm.). |
Home range is about 60-350 m2. This species is basically solitary and territorial, with strict intrasexual avoidance indicated. In spring, areas around occupied burrows have a more lush growth of herbaceous vegetation than do areas between burrow systems; this growth is eventually removed by grazing by livestock and/or kangaroo rats (Williams and Kilburn 1991). Digging and feeding activity promote the establishment of exotic weeds, which in turn are a favoured food source (Schiffman 1994). Giant kangaroo rats feed on seeds, especially those of Lepidium nitidum, oenothera, Bromus rubens, and Erodium cicutarium. They also eat some green herbaceous vegetation and occasionally insects. In some localities. They gather dry grass into "haystacks" to cure, later removing seeds for storage in underground burrows. They also temporarily bury seeds in the ground before storing in burrows. Giant kangaroo rats emerge to forage soon after sunset in spring. They spend a little less than two hours per night above ground actively foraging in spring-summer (Braun 1985).
Limited data indicate that the reproductive season may extend from January through May (Williams and Kilburn 1991) (February to June or perhaps later according to Biosystems Analysis 1989). Gestation lasts about one month. Litter size is three to six (Biosystems Analysis 1989); average litter size is probably four (Williams and Kilburn 1991). Young are weaned at four weeks (Matthews and Moseley 1990).
The decline is largely a result of conversion of habitat to agricultural uses, combined with additional loss of habitat to industrial uses (e.g., petroleum exploration and extraction) and urbanization, and population reductions and extirpations from rodenticide use (aimed at California ground squirrel and historically at kangaroo rats) (Williams 1992, USFWS 1998). Possibly excessive livestock grazing may have contributed to the decline in some areas (livestock may crush near-surface burrows and compete for food with kangaroo rats) (see USFWS 1998). Between 1972 and 1980 most of the remaining habitat was converted from native vegetation to cultivated agricultural crops due in part to an abundance of irrigation water supplied by recently completed water delivery systems.
More recently, the conversion of habitat to agricultural uses has slowed substantially, but urban and industrial developments, petroleum and mineral exploration and extraction, new energy and water conveyance facilities, and construction of communication and transportation infrastructures continue to destroy habitat and increase the threats to the species by reducing and further fragmenting populations (USFWS 1998). Habitat degradation due to lack of appropriate habitat management on conservation lands, especially lack of grazing or fire to control density of vegetation (including shrubs) may be a threat (Williams and Germano 1993).
Dipodomys ingens was listed as Endangered by both the California Fish and Game Commission (in 1980) and the United States Fish and Wildlife Service (in 1987). Habitat is protected to varying degrees at Carrizo Plain National Monument, U.S. Department of Energy Naval Petroleum Reserves in western Kern County, and certain BLM lands. Parcels in the Lokern area of western Kern County have been protected by the California Energy Commission, California Department of Fish and Game, and The Nature Conservancy.
Habitat for three of the six regional populations (Cuyama Valley, Kettleman Hills, and San Juan Creek Valley) include no public or conservation lands; all are small and vulnerable to extirpation from demographic and random catastrophic events (e.g., drought, flooding, fire), and inappropriate land uses that would degrade or destroy habitat (USFWS 1998).
Future conservation actions require an adequate understanding of compatible land uses and management prescriptions that provide optimum habitat conditions (Williams and Germano 1993). Data should be collected on demography, dispersal, and reproduction, as well as the status of populations occurring on private lands in the Cuyama Valley, San Juan Creek area, and Ciervo/Tumey Hills. See USFWS (1998) for specific protection, management, and monitoring needs.
|Citation:||Linzey, A.V. & NatureServe (Williams, D.F. & Hammerson, G.). 2008. Dipodomys ingens. The IUCN Red List of Threatened Species 2008: e.T6678A12794494.Downloaded on 23 June 2018.|
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