Critter Catalog

What do they look like?

The bodies of Nelson's antelope squirrels are widest in the middle. They have small, rounded ears, short legs, and short tails. The back of their heads and necks and also the outside of their legs are dull yellowish-brown or tan. Their tails have thick hair and their underside is light grey or white. They have a light-colored stripe running along the side of the body starting at the shoulder. Males are a little bit bigger than females, measuring 234 to 267 mm, but usually around 249 mm. Females are 230 to 256 mm long, and usually around 238 mm. Nelson's antelope squirrels have different summer and winter fur colors. Their fur is darker in the fall and winter. The look a lot like white-tailed antelope squirrels, but are bigger and their fur is more gray. (Best, 1999; Brown and Williams, 2006; Merriam, 1983)

• Other Physical Features
• endothermic
• homoiothermic
• bilateral symmetry

• Sexual Dimorphism
• male larger

• Range mass

  142 to 179 g

  5.00 to 6.31 oz

• Average mass

  155 g

  5.46 oz

• Range length

  230 to 267 mm

  9.06 to 10.51 in

• Average length

  249 mm

  9.80 in

• Average basal metabolic rate

  0.8 cm3.O2/g/hr

Where do they live?

Nelson's antelope squirrels only live in California. They lives in the lowest parts of the San Joaquin valley, the Cuyama and Panoche valleys in San Luis Obispo county, and the Carrizo and Elkhorn plains. (Best, et al., 1990; Taylor, 1918)

• Biogeographic Regions
• nearctic
  • native

What kind of habitat do they need?

Nelson's antelope squirrels are found in low, hot deserts. In North America, their habitats are found in Texas, New Mexico, Arizona, Nevada, and California. They live in dry grasslands and places with lots of shrubs. They can live in places with just a few or some shrubs and usually live with plants that live in dry environments. They like soils with clay, sand, and silt that are about 50 to 1100 meters elevation. They use burrows of kangaroo rats, so they might only live where there are kanagaroo rats. (Grinell and Dixon, 1918; Hawbecker, 1953; Merriam, 1898; Whitaker, et al., 2008)

• These animals are found in the following types of habitat
• temperate
• terrestrial

• Terrestrial Biomes
• desert or dune

• Range elevation

  50 to 1100 m

  164.04 to 3608.92 ft

How do they reproduce?

Both male and female Nelson's antelope squirrels have multiple mates. Usually they find mates within the area where they usually live, but females will also travel up to 1 km away looking for a mate. ("Five Year Status Report- Ammospermophilus nelsoni", 1987; Hawbecker, 1947)

• Mating System
• polygynandrous (promiscuous)

Nelson's antelope squirrels breed from late winter to early spring. The young develop inside the mother for 26 days. Then, females give birth in burrows underground. They have 6 to 11 young at a time, but usually around 9. The young stay underground for about the first 30 days after they are born. They drink their mother's milk. Sometimes they start eating solid food before they come out of the burrow, and other times not until after. Females get the young to stop drinking milk by refusing to give it to them and returning to the burrow less often. Males can breed earlier in their lives than females. (Best, et al., 1990; Best, 1999; Macdonald, 2009)

• Key Reproductive Features
• iteroparous
• seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual
• viviparous

• How often does reproduction occur?

  Nelson's antelope squirrels breed once annually.

• Breeding season

  Nelson's antelope squirrels breed from late winter to early spring.

• Range number of offspring

  6 to 11

• Average number of offspring

  9

• Range gestation period

  25 to 30 days

• Average gestation period

  26 days

• Range weaning age

  30 (high) days

• Average weaning age

  15 days

• Range time to independence

  3 to 4 weeks

• Average age at sexual or reproductive maturity (female)

  377 days

• Average age at sexual or reproductive maturity (male)

  377 days

Young Nelson's antelope squirrels can't feed themselves right after they are born. Females give them milk and teach them to eat solid food, and males don't play a big role in caring for them. Mothers get their young to stop drinking their milk by staying farther away and not responding to them. Even after they stop drinking milk, mothers stay in contact by visiting their young and calling to them. (Best, et al., 1990)

• Parental Investment
• altricial
• female parental care
• pre-fertilization
  • provisioning
  • protecting
    • female
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female
• pre-weaning/fledging
  • provisioning
    • female
  • protecting
    • female

How long do they live?

In the wild, Nelson's antelope squirrels usually live for less than 1 year. Their babies and young are much more likely to die. They can live about 4 years in captivity, and the longest one ever lived in captivity was 5.7 years. About 80% of them die every year. They average lifespan is just 8 months. (Best, et al., 1990; Hawbecker, 1975)

• Range lifespan
  Status: captivity

  5.7 (high) years

• Average lifespan
  Status: wild

  8 months

• Average lifespan
  Status: captivity

  4 years

How do they behave?

Nelson's antelope squirrels live in small family groups of 6 to 8 squirrels. They are closely related to white-tailed antelope squirrels, who have strict social organization. They keep up their social organization using body language and fighting. Nelson's antelope squirrels are very similar to them in a lot of ways, and might do this too. ("Five Year Status Report- Ammospermophilus nelsoni", 1987; Belk and Smith, 1991; Best, et al., 1990; Best, 1999; Grinell and Dixon, 1918; Hawbecker, 1947; Hawbecker, 1953; Hawbecker, 1975)

• Key Behaviors
• terricolous
• fossorial
• diurnal
• crepuscular
• motile
• sedentary
• territorial
• social

• Average territory size

  0.044 km^2

Home Range

Males and females usually live and travel in an area about 4.4 hectares. They tend to clump together within these areas in the best parts of their habitat. The farthest away from their home area males travel is 1,260 m and the fatherst away from their home area females travel is 900 m. (Best, et al., 1990)

How do they communicate with each other?

Nelson's antelope squirrels mostly use hearing, smell, and sight. They look around before deciding to leave their burrows. They use their sense of smell to decide if there is danger, to find food, and communicate. They make alarm calls to warn others about nearby predators, especially if they are in closed-off areas. They make low-pitched trills that are actually made by shaking their body instead of their voice. Females also make this noise to communicate with their young. Nelson's antelope squirrels twitch their tails quickly when they are frightened or excited. (Best, et al., 1990; Best, 1999; Bolles, 1988)

• Communication Channels
• visual
• acoustic
• chemical

• Perception Channels
• tactile
• acoustic
• chemical

What do they eat?

Nelson’s antelope squirrels eat both animals and plants. Their biggest sources of food are insects, green plants, and seeds. They sometimes eat other small animals. They eat rodents, lizards and other Nelson's antelope squirrels that have died. They prefer to eat plants with a lot of water in them, since they don't live near water. Some plants they prefer are red-stemmed filaree and red brome. Other plants they eat are ephedra, clover, and locoweed. If there aren't many plants available that have a lot of water, they eat turpine weed. When plants and insects aren't available, they eat seeds. Nelson's antelope squirrels squat on their back legs with their tail up to eat, holding food in their front paws. (Hawbecker, 1947; Macdonald, 2009)

• Primary Diet
• carnivore
  • eats terrestrial vertebrates
  • insectivore
  • scavenger
• herbivore
  • folivore
  • granivore
• omnivore

• Animal Foods
• reptiles
• carrion
• insects

• Plant Foods
• leaves
• seeds, grains, and nuts

• Foraging Behavior
• stores or caches food

What eats them and how do they avoid being eaten?

Nelson's antelope squirrels warn each other about predators and also avoid them. They hide in burrows of kangaroo rats, and check their surroundings carefully before they come out. Above ground, they hide in shrubs, and their light brown fur camouflages them in the desert. When they search for food, they stay close to the ground and move with short, quick jumps. Nelson's antelope squirrels use their sense of smell to get away from danger quickly. They communicate to each other about predators using alarm calls. They may also be able to understand warning calls of birds like horned larks and white-crowned sparrows. Their most important predators are American badgers, who dig into the burrows to eat both young and adults. They are also eaten by coyotes and kit foxes. ("Five Year Status Report- Ammospermophilus nelsoni", 1987; Best, et al., 1990; Brown and Williams, 2006)

• These animal colors help protect them
• cryptic

• Known Predators

  • American badgers (Taxidea taxus)
  • coyotes (Canis latrans)
  • kit foxes (Vulpes macrotis)

What roles do they have in the ecosystem?

Nelson's antelope squirrels are eaten by medium-sized predators. They get parasites inside and outside their bodies. They get tapeworms, roundworms (called Spirura infundibuliformis and Physaloptera spinicauda), and also thorny-headed worms. Outside their bodies, they get fleas and ticks. Nelson's antelope squirrels benefit from kangaroo rats, because they use their burrows. They further impact their habitat by continuing to burrow. They also collect seeds and disperse them. (Best, et al., 1990)

• Ecosystem Impact
• disperses seeds
• creates habitat

Do they cause problems?

Nelson's antelope squirrels can get infected with diseases like western equine encephalomyelitis, St. Louis encephalitis, Powassan virus, and Modoc virus. However, they have never spread disease to humans. (Best, et al., 1990)

How do they interact with us?

Nelson’s antelope squirrels don't usually live close to humans. They eat insects that can be pests and also spread the seeds they gather and store. (Belk and Smith, 1991; Hawbecker, 1947)

Are they endangered?

Nelson’s antelope squirrels are endangered, according to the IUCN Red List. A lot of their habitat has been destroyed because of farming and humans building bigger cities. They are also affected when animals raised by humans eat the plants they do, and by chemicals that are used to kill rodents and insects. California's Endangered Species Recovery Program has a list of ways to conserve them, like protecting their habitat and reintroducing them into protected areas. ("Five Year Status Report- Ammospermophilus nelsoni", 1987; Best, et al., 1990; Brown and Williams, 2006; Grinell and Dixon, 1918)

• IUCN Red List

  Endangered

• US Federal List

  No special status

• CITES

  No special status

• State of Michigan List

  No special status

Some more information...

There are a lot of fossils of the relatives of Nelson's antelope squirrels. They probably became their own species between 5.3 and 23 million years ago. (Best, et al., 1990; Hawbecker, 1953)

Contributors

Divya Balaji (author), Yale University, Eric Sargis (editor), Yale University, Rachel Racicot (editor), Yale University, Tanya Dewey (editor), University of Michigan-Ann Arbor, Catherine Kent (editor), Special Projects.

References

California Department of Fish and Game. Five Year Status Report- Ammospermophilus nelsoni. EW87. Turlock: Calif. Dep. of Fish and Game, Nongame Bird and Mammal Sec. rep. 1987.

Belk, M., D. Smith. 1991. Ammospermophilus leucurus. Mammalian Species, 368: 1-8.

Best, T. 1999. Ammospermophilus nelsoni. Pp. 407-408 in D Wilson, S Ruff, eds. Smithsonian Book of North American Mammals, Vol. 1999, 1999 Edition. British Columbia: UBC press.

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

Bolles, K. 1988. The Evolution and variation of antipredator vocalizations of antelope squirrels. Zeitschrift für Säugetierkunde, 53: 129-147.

Brown, N., D. Williams. 2006. "Endangered Species Recovery Program" (On-line). San Joaquin antelope squirrel Ammospermophilus nelsoni. Accessed April 30, 2012 at http://esrp.csustan.edu/speciesprofiles/profile.php?sp=amne.

Cypher, B. 2001. Spaciotemporal Variation in Rodent Abundance in the San Joaquin Valley. The Southwestern Naturalist, 46/1: 66-75.

Grinell, J. 1933. Review of the Recent mammal fauna of California. Berkeley, California: University of California.

Grinell, J., J. Dixon. 1918. Natural History of the Ground Squirrels of California. Sacramento, California: California State Printing Office.

Hawbecker, A. 1975. The Biology of Some Desert Dwelling Ground Squirrels. The Hague, Netherlands: Dr. Junk, b.v.

Hawbecker, A. 1953. Environment of the Nelson Antelope Ground Squirrel. Journal of Mammalogy, 34/3: 324-334.

Hawbecker, A. 1947. Food and Moisture Requirements of the Nelsons Antelope Ground Squirrel. Journal of Mammalogy, 28/2: 115-125.

Hawbecker, A. 1958. Survival and Home Range in the Nelson’s antelope squirrel. Journal of Mammalogy, 39: 207-215.

Heller, C., J. Henderson. 1976. Hypothalamic Thermosensitivity and Regulation of Heat Storage Behavior in a Day-active Desert Rodent Ammospermophilus nelsoni. Journal of Comparative Physiology, 108: 255-270.

Macdonald, D. 2009. Rodentia. Pp. 128-166 in D Macdonald, ed. The Encyclopedia of Mammals, Vol. 2009, 2nd revised Edition. Oxford: Oxford University Press.

Merriam, H. 1898. Life Zones and Crop Zones of the United States. Washington D.C: Government Printing Office.

Merriam, H. 1983. Descriptions of eight new ground squirrels of the genera Spermophilus and Tamias from California, Texas, and Mexico. Proceedings of the Biological Society of Washington, 8: 129-138.

Taylor, W. 1918. A New Spermophile from the San Joaquin Valley California with notes on Ammospermophilus nelsoni nelsoni Merriam. Berkeley, Califronia: University of California Press.

Tevis, L. 1953. Stomach Contents of Chipmunks and Mantled Squirrels in Northeastern California. Journal of Mammalogy, 34/3: 316-324.

Whitaker, J., G. Hammerson, D. Williams. 2008. "Ammospermophilus nelsoni" (On-line). IUCN Red list of Threatened Species. Accessed April 30, 2012 at http://www.iucnredlist.org/apps/redlist/details/1149/0.