|Scientific Name:||Dipodomys nitratoides|
|Species Authority:||Merriam, 1894|
|Red List Category & Criteria:||Vulnerable B1ab(i,ii,iii,v) ver 3.1|
|Assessor/s:||Linzey, A.V. & NatureServe (Hammerson, G. & Williams, D.F.)|
|Reviewer/s:||Amori, G. (Small Nonvolant Mammal Red List Authority) & Chanson, J. (Global Mammal Assessment Team)|
Listed as Vulnerable, although it was historically widespread, its extent of occurrence is now less than 20,000 km², its range is severely fragmented, much of the habitat of the species has been destroyed by farming activities and no high quality habitat is protected, and declines in extent and quality of habitat continue.
|Range Description:||The range of this species encompasses part of the San Joaquin Valley and adjacent valleys, in California in the United States, from the valley floor in Merced County, south of the Merced and San Joaquin rivers, to the southern edge of the valley, and the Panoche Valley (eastern San Benito County), the Carrizo Plain (San Luis Obispo County), and the upper Cuyama Valley (San Luis Obispo and Santa Barbara counties), at elevations of 50-800 metres (Best 1991, Williams et al. 1993).|
Native:United States (California)
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||The total adult population size is unknown but appears to be at least a few 100,000s. Local population size tends to exhibit large fluctuations. Reported densities are generally between 5-20 per hectare. It is represented by numerous relatively small populations found throughout most of the historical range that spanned several million acres.|
|Habitat and Ecology:||
Habitat includes friable sandy or silty soils in areas with no to moderate shrub cover and scattered herbaceous plants: sparsely vegetated alkali sink communities where soils are generally sandy or silty; valley grassland; saltbush and sink scrub. The species does not tolerate irrigation or cultivation but may reinvade fields no longer under cultivation.
Habitats in order of decreasing favourability: (1) level to gently sloping areas with sparse to moderate shrub cover in alkali desert scrub and valley grassland, (2) ridge tops and steep slopes with sandy, friable soils and scattered shrubs in alkali desert scrub and valley grassland, (3) sandy arroyos and dry stream beds in above associations, and (4) arid annual grasslands with alkaline, friable soils.
When inactive, it occupies underground burrows; burrows in hummocks (e.g., around base of shrub); burrow systems are shallow but often extensive. Young are born in underground burrows. Breeding season is reported to be December-August or throughout the year (Best 1991). Reproductive activity starts in late February and continues until September, with a peak in April. Gestation lasts 31-35 days. Litter size is 1-3, usually two. Young leave nest at about three weeks. Females will have up to three litters per year.
Feeds on seeds (e.g., those of erodium, capsella bursapastoris, and atriplex). Also consumes some insects and green vegetation in the spring. May cache seeds in small pits in the walls of the burrow system.
Habitat has been reduced and fragmented primarily as a result of agricultural development, with additional losses due to urbanization, associated transportation infrastructure, and invasion by exotic grasses (USFWS 1998). Most extant habitat is of poor or marginal quality, is unprotected in private ownership, and in rapidly developing areas. Some populations have been negatively affected by rodenticides.
Populations of this species periodically increase to high levels and decline rapidly (due to long-term drought, excessive amounts of precipitation, flooding, or other factors). Sometimes these fluctuations lead to local extirpation (USFWS 1998). When large expanses of connected habitat existed, local extinction was not a great problem because some surviving populations eventually increased, and individuals recolonized areas where they had been eliminated (USFWS 1998). Current population fragmentation inhibits or prevents such recolonization. Fragmentation, isolation, and subsequent extirpation without recolonization has greatly affected subspecies exilis and may now be in progress in subspecies nitratoides (USFWS 1998).
Subspecies exilis and nitratoides are listed by United States Fish and Wildlife Service (USFWS) as Endangered. Most protected occurrences are for the unlisted subspecies brevinasus on the Carrizo Plain; few protected occurrences are of the listed subspecies exilis or nitratoides. Subspecies nitratoides current range includes Pixley National Wildlife Refuge, Allensworth Ecological Preserve, and TNC lands at Paine Wildflower Preserve (Matthews and Moseley 1990). For subspecies exilis, about 85 percent of the 347 hectares of designated Critical Habitat has been acquired, but these lands generally have not been appropriately managed for kangaroo rats (see USFWS 1998). Most of the critical habitat is within state Alkali Sink Ecological Reserve; about nine hectares are part of the Mendota Wildlife Management Area; the rest is privately owned (Matthews and Moseley 1990, USFWS 1998).
Efforts to locate populations of subspecies exilis should be continued and intensified (USFWS 1998). Further inventory of subspecies brevinasus is needed. Remaining suitable habitat needs to be protected from development or conversion to incompatible uses.
The relationship between population density and habitat quality needs to be assessed, and more data on demographics, reproduction, and impacts of grazing and fire are needed. Taxonomic status of the nominal subspecies and of various populations needs to be resolved.
|Citation:||Linzey, A.V. & NatureServe (Hammerson, G. & Williams, D.F.) 2008. Dipodomys nitratoides. In: IUCN 2012. IUCN Red List of Threatened Species. Version 2012.2. <www.iucnredlist.org>. Downloaded on 19 June 2013.|