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Ammospermophilus nelsoni

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA CHORDATA MAMMALIA RODENTIA SCIURIDAE

Scientific Name: Ammospermophilus nelsoni
Species Authority: (Merriam, 1893)
Common Name/s:
English Nelson's Antelope Squirrel, San Joaquin Antelope Ground Squirrel, San Joaquin Antelope Squirrel

Assessment Information [top]

Red List Category & Criteria: Endangered B1ab(iii) ver 3.1
Year Published: 2008
Date Assessed: 2008-06-30
Assessor/s: Whitaker Jr., J.O. & NatureServe (Hammerson, G. & Williams, D.F.)
Reviewer/s: Amori, G. (Small Nonvolant Mammal Red List Authority) & Chanson, J. (Global Mammal Assessment Team)
Justification:
Listed as Endangered because its extent of occurrence is less than 5,000 km², its range is severely fragmented and there is ongoing decline in the extent and quality of its habitat.
History:
2000 Endangered
1996 Endangered

Geographic Range [top]

Range Description: The species' range is restricted to the central and western San Joaquin Valley and neighbouring areas to the west in the inner Coast Ranges of California in the United States (e.g., Cuyama Valley, Panoche Valley, Carrizo Plain, Elkhorn Plain) (Best et al. 1990). Its elevational range extends from about 50 m asl on the floor of the San Joaquin Valley to around 1,100 m asl in the Temblor Range, but antelope squirrels are not common above about 800 m asl on the ridges and plains west of the San Joaquin Valley proper (Williams 1980; D.F. Williams, unpubl. data). Populations now exist primarily in marginal habitats of low foothills and mountains on the western edge of the San Joaquin Valley; significant populations occur only in western Kern County at Elk Hills and on portions of the Carrizo and Elkhorn plains. In the northern part of the range, low density populations occur in the Panoche and Kettleman hills (California Department of Fish and Game 1990, Harris and Stearns 1991).
Countries:
Native:
United States (California)
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: The total population size is unknown. Based on 3-10 squirrels per hectare on 41,300 hectares of the best remaining habitat (Williams 1980), population size would be at least 124,000-413,000. The species is common within the Carrizo Plain National Monument.

This species is represented by several dozen distinct occurrences or subpopulations. It occurs at scattered sites in low density throughout much of the historical range. Moderate efforts have been made at locating populations.

The current trend is not well known but, since 1979, populations have disappeared from many of the smaller habitat clusters on the floor of the San Joaquin Valley (Williams 1980, USFWS 1998). However, recent protection efforts in the southwestern San Joaquin Valley likely have slowed the rate of decline, and the species remains common in some protected areas. Probably the rate of decline is less than 30% over the past 10 years.

Prior to cultivation, the area within which this species was distributed was approximately 3.5 million acres (about 14,000 square kilometres = historical extent of occurrence). The species is presently extant in less than 20% of its former range. In 1979, extant, uncultivated habitat (but including land occupied by towns, roads, canals, pipelines, strip mines, airports, oil wells, and other developments) for the species was estimated at 275,200 hectares (680,000 acres, 2,752 sqkm) (Williams 1980). None of the best historical habitat remained.

One study indicated that densities in open Ephedra plots and shrubless plots ranged from 0.8 to 8.0 squirrels per hectare, but all but two sites had densities of four or less per hectare. Densities on shrubless, grassy dominated sites were equal to or higher than those on shrubby sites (Harris and Stearns, 1991).
Population Trend: Decreasing

Habitat and Ecology [top]

Habitat and Ecology: Habitat consists of dry flat or rolling terrain, with slopes less than 10-14 degrees, on alluvial and loamy soils, soils with sandy or gravelly texture, or fine-grained soils that are nearly brick-hard when dry. The species inhabits grassy, sparsely shrubby ground (shrubs include saltbush, ephedra, bladder pod, goldenbush, snakeweed, etc.); it also occurs in areas lacking shrubs where giant kangaroo rats are present.

Habitats in order of decreasing favourability: (1) xerophytic stage of alkali desert scrub with shrubs sparsely distributed and with friable soils, at elevations greater than 4,000 feet, (2) annual grassland with less than six inches annual precipitation, friable soils, and abundance of Dipodomys ingens, (3) halophytic stage of alkali desert scrub with shrubs sparsely distributed and with friable soils, at elevations above 2,200 feet, and (4) annual grassland with 7-9 inches annual precipitation and abundance of Dipodomys heermanni. Habitats that are avoided included valley floor areas of alkaline soils, iodine bush, and spring saltbush, probably due to high water tables (Biosystems Analysis 1989). See also Best et al. (1990) for habitat synopsis. These squirrels seldom dig their own burrows; most often they use burrows made by other small mammals. Preferred burrow locations are under shrubs, in the banks of arroyos at the base of alluvial fans, and along roadcuts, pipelines, and drilling platforms (Biosystems Analysis 1989).

Breeding season coincides with availability of green vegetation. Young are born in March, first seen above ground about the first week of April, at which time they gather food. Gestation lasts 26 days. One breeding season per year. Litter size is 6-12 (average nine). May live five plus years, though usual life span is less than one year.

Half of the remaining habitat supports fewer than one animal per hectare, 15% of the remaining habitat supports 3-10 animals per hectare (generally four or fewer per hectare, California Department of Fish and Game 1990). <Spermophilus beecheyi reportedly may restrict the range of A. nelsoni (see Best et al. 1990). Among several predators, badger is most important. Lives in small groups.

It is omnivorous, and the diet is mainly green vegetation, grass and forb seeds, and insects. It feeds on insects during the dry season, from mid-April to December. Green vegetation is important December-April. Generally stays underground when air temperature is less than 10C (California Department of Fish and Game 1990). Little activity in hot weather, when most active in morning and late afternoon. No evidence of hibernation or aestivation, yet reported to become fat in late spring and disappear during hot months (Best et al. 1990).
Systems: Terrestrial

Threats [top]

Major Threat(s): The decline is a result of loss of habitat due to agricultural and urban development as well as oil and gas exploration practices. Primary existing threats include loss of habitat due to agricultural development, urbanization, and petroleum extraction, and the use of rodenticides for ground squirrel control. Overgrazing and associated loss of shrub cover is a concern in some areas. These threats will be alleviated by the implementation of the San Joaquin Endangered Species Recovery Plan.

Conservation Actions [top]

Conservation Actions: The species is currently listed as Threatened by the California Fish and Game Commission and it is a federal C2 candidate taxon.

Significant populations occur on the Carrizo Plain National Monument (encompasses most of the Carrizo Plain and Elkhorn Plain). The national monument designation applies only to public lands managed by the Bureau of Land Management. Existing private lands within the monument boundaries are not affected by the designation. The overall Carrizo Plain, which includes some state owned land, will continue to be jointly managed by the Bureau of Land Management, the California Department of Fish and Game, and The Nature Conservancy.

Small populations are also found within two preserves in Kern County owned by The Nature Conservancy, and two reserves owned by the California Department of Fish and Game (in Kern County and Tulare County). See California Department of Fish and Game (1990) for brief comments on protected areas inhabited by this species (e.g., Elkhorn Plain Ecological Preserve, Carrizo Plain, and others).

The California Department of Fish and Game is involved in several conservation efforts, including the Metropolitan Bakersfield Habitat Conservation Plan (HCP), the California Department of Corrections Electric Fence HCP, the Coles Levee area 2081 Agreement, and the Arco Western Energy HCP.

Acquisition and protection of lands with extant populations of antelope squirrels in the Panoche and Kettleman Hills and on the San Joaquin Valley floor should be the highest priority for this species (Harris and Stearns 1991). Also need to determine the population density for the range of habitats occupied; additional inventories are needed, mostly on private land, and also to monitor populations, and obtain data on demography, dispersal, and reproduction.

USFWS (1998) stated that the actions required to conserve the San Joaquin antelope squirrel, in approximate order of importance, are: 1. Determine habitat management prescriptions on the southern San Joaquin Valley floor. 2. Inventory potential habitat in the Allensworth, Semitropic Ridge, and Kettleman Hills natural areas, and along the western edge of the Valley between Pleasant Valley, Fresno County, and McKittrick Valley-Lokern Area, Kern County. 3. Protect additional habitat in the Pixley National Wildlife Refuge-Allensworth Natural Area. 4. Develop and implement a population monitoring program at sites representative of their existing geographic range. 5. Protect additional habitat in the Panoche Region of western Fresno and eastern San Benito Counties. 6. Protect additional habitat in western Kern County. 7. Protect additional habitat in the Semitropic Ridge Natural Area. 8. Reevaluate the status of San Joaquin antelope squirrels within three years of recovery plan approval.

Management Requirements: Protect habitat from overgrazing and loss of shrub cover; maintain sparse shrub cover and associated species; avoid unnecessary rodenticide use. Care should be taken not to destroy burrows near man-made structures in previously disturbed sites (Biosystems Analysis 1989).

Bibliography [top]

Best, T. L., Titus, A. S., Lewis, C. L. and Caesar, K. 1990. Ammospermophilus nelsoni. Mammalian Species 367: 1-7.

California Department of Fish and Game. 1990. 1989 annual report on the status of California's state listed threatened and endangered plants and animals. California Department of Fish and Game, Sacramento, CA, USA.

Hafner, D. J., Yensen, E. and Kirkland Jr., G. L. 1998. Status survey and conservation action plan - North American Rodents. IUCN/SSC Rodent Specialist Group, Gland, Switzerland.

Harris, J. H. and Stearns, D. M. 1991. Population density, census methods, habitat relationships and home range of the San Joaquin Antelope Squirrel, 1988-89. California Department of Fish and Game, Nongame Bird and Mammal Section Report.

U. S. Fish and Wildlife Service. 1998. Recovery plan for upland species of the San Joaquin Valley, California. Portland, OR, USA.

Williams, D. F. 1980. Distribution and population status of the San Joaquin antelope squirrel and giant kangaroo rat. California Department of Fish and Game, Nongame Wildl. Invest.

Wilson, D. E. and Ruff, S. 1999. The Smithsonian Book of North American Mammals. Smithsonian Institution Press, Washington, DC, USA.

Citation: Whitaker Jr., J.O. & NatureServe (Hammerson, G. & Williams, D.F.) 2008. Ammospermophilus nelsoni. In: IUCN 2013. IUCN Red List of Threatened Species. Version 2013.2. <www.iucnredlist.org>. Downloaded on 20 April 2014.
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