Nelson's antelope squirrel (Ammospermophilus nelsoni)

Description

Nelson's antelope squirrel fact file

• Description
• Biology
• Range
• Habitat
• Status
• Threats
• Conservation
• Find out more
• Glossary
• References
• Print factsheet

Nelson's antelope squirrel description

A highly sociable and conspicuous species, groups of Nelson’s antelope squirrels (Ammospermophilus nelsoni) are commonly seen scampering across the grassy hills of San Joaquin Valley, California ^{(3) (4)}. This diminutive, ground-dwelling rodent has a cylindrical body with short, yet robust, legs; small, rounded ears and a large, bushy tail ^{(5) (6)}. Touch sensitive whiskers protrude from the snout and white rings surround the large eyes, which are positioned on the side of the head to a provide a broad field of vision ⁽⁵⁾. The pelage is a buffy-tan and reddish-brown colour, with white stripes extending down the sides of the body, towards a light greyish tail ^{(3) (6)}. When feeding, Nelson’s antelope squirrel assumes a distinctive posture, squatting on its rear limbs with the tail cocked behind the back, whilst holding its food in the forepaws. Morsels of food are chiselled with a pair of enlarged incisors and broken down by abrasive cheek teeth ⁽⁵⁾.

Also known as

San Joaquin antelope ground squirrel, San Joaquin antelope squirrel.

Size

Male head-body length: 23.4 – 26.7 cm ⁽²⁾

Female head-body length: 23 – 25.6 cm ⁽²⁾

Weight

142 – 179 g ⁽²⁾

Nelson's antelope squirrel biology

Most active at dusk and dawn, Nelson’s antelope squirrel shelters in burrows during the hotter parts of the day. Extensive networks of burrows with up to six openings may be dug under tussocks of vegetation, or the old burrows of other ground-dwelling mammals may be re-used ⁽⁶⁾. Although many ground squirrels hibernate in their burrows during winter months, Nelson’s antelope squirrel is active year round, reducing its body temperature during cooler periods to save energy expenditure ^{(6) (7)}. For most of the year, green vegetation forms the bulk of its diet, but during the dry season, it commonly forages for insects ⁽¹⁾. Food is carried in cheek pouches and may be cached in burrows or under rocks, and consumed later when food is in short supply ⁽³⁾.

Breeding takes place over winter, when mature females will typically mate with several males ^{(5) (6)}. A single litter of around nine infants is produced after a gestation period of around 26 days, with birthing coinciding with a peak in green vegetation productivity ^{(1) (6) (8)}. Juveniles develop rapidly, becoming independent after three to four weeks, but most juveniles will not live beyond one year due to high levels of predation ^{(5) (8)}. Juveniles usually stay within the home range of the family, but some will travel up to one kilometre to find a mate ⁽⁴⁾.

Nelson's antelope squirrel range

Historically, Nelson’s antelope squirrel had a fairly large range, estimated at around 14,000 square kilometres, across central California in the United States ⁽⁶⁾. However, this species has disappeared from many areas, and is now largely confined to the western San Joaquin Valley and bordering valleys to the west in the inner Coast Ranges ⁽¹⁾. The species’ total range is now estimated at less than 3,000 square kilometres, of which only 400 square kilometres are described as good quality habitat ⁽⁶⁾. The bulk of the population is found at Elk Hills and on the Carrizo and Elkhorn Plains in Kern County, while the only significant populations in the northern part of the species’ range are at the Panoche and Kettleman Hills ⁽¹⁾.  

Nelson's antelope squirrel habitat

Nelson’s antelope squirrel is found on dry, gently rolling grassy hills with sparse shrubs, on alluvial and sandy soils, between 50 and 1,100 metres above sea level ⁽¹⁾.

Nelson's antelope squirrel status

Nelson's antelope squirrel is classified as Endangered (EN) on the IUCN Red List ⁽¹⁾.

Nelson's antelope squirrel threats

The principal reason behind the dramatic decline of Nelson’s antelope squirrel is the loss of its habitat to agricultural encroachment, urbanisation, overgrazing by livestock, and oil and gas exploration. Now present in only 20 percent of its former range, Nelson’s antelope squirrel is extremely vulnerable to further habitat loss. In public owned reserves this rare species is protected from further declines, but in private owned areas, where the future management is uncertain, its habitat is still threatened. The use of insecticides on agricultural pests has also been identified as a further threat to Nelson’s antelope squirrel, due to loss of prey, while the historical use of rodenticides for the control of ground squirrels may have also contributed to the decline ^{(1) (6)}.  

Nelson's antelope squirrel conservation

Nelson’s antelope squirrel has already benefited from several conservation measures aiming to protect its vulnerable habitat.  Several reserves have been created within the San Joaquin valley, an area defined by a high degree of endemism, including the Carrizo Plain National Monument and the Elkhorn Plain Ecological Preserve. This has offered Nelson’s antelope squirrel some sanctuary; however, several sites with substantial populations still receive no form of protection. Foremost in the drive to save this species should be the establishment of further protected areas in the Panoche and Kettleman hills and on the San Joaquin valley floor ⁽¹⁾. Furthermore, livestock grazing of natural grasslands should be limited, while further surveys and monitoring of the density of this curious species is also required ⁽⁶⁾.

View information on this species at the UNEP World Conservation Monitoring Centre.

Find out more

For more information on the conservation of the San Joaquin Valley: 

• The Nature Conservancy:
  http://www.nature.org/wherewework/northamerica/states/california/preserves/art6322.html

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Glossary

Alluvial

Relating to the sediment deposited by flowing water, as in a riverbed, flood plain, or delta.

Endemism

The degree to which a species or taxonomic group is confined to a single region.

Gestation

The state of being pregnant; the period from conception to birth.

Hibernate

Hibernation is a winter survival strategy characteristic of some mammals in which an animal’s metabolic rate slows down and a state of deep sleep is attained. Whilst hibernating, animals survive on stored reserves of fat that they have accumulated in summer.

Pelage

The coat of a mammal, composed of fur, hair or wool, covering the bare skin.

References

1. IUCN Red List (March, 2010)
   http://www.iucnredlist.org/
2. Smithsonian National Museum of Natural History (March, 2010)
   http://www.mnh.si.edu/mna/image_info.cfm?species_id=3
3. Nowak, R.M. (1999) Mammals of the World. The John Hopkins University Press, Baltimore.
4. Best, T.L., Titus, A.S., Lewis, C.L. and Caesar, K. (1990) Ammospermophilus nelsoni. Mammalian Species, 367: 1-7.
5. Macdonald, D.W. (2009) The Encyclopedia of Mammals. Oxford University Press, Oxford.
6. U.S Fish and Wildlife Service. (1998) Recovery Plan for Upland Species of the San Joaquin Valley, California. Portland, USA. Available at:
   http://esrp.csustan.edu/publications/pubhtml.php?doc=sjvrp&file=chapter02M02.html
7. Chappell, M.A. and Bartholomew, G.A. (1981) Activity and thermoregulation of the antelope ground squirrel Ammospermophilus leucurus in winter and summer. Physiological Zoology, 54: 215-223.
8. The Animal Ageing and Longevity Database (March, 2010)
   http://genomics.senescence.info/species/entry.php?species=Ammospermophilus_nelsoni