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Mohave ground squirrel

Spermophilus mohavensis

What do they look like?

The overall body length of Mohave ground squirrels ranges from 210 to 230 mm in adults, their tail lengths range from 42 to 72 mm and they weigh 85 to 130 grams. These squirrels have all brown fur, with no spots or stripes. They have a short, broad, flat, furry tail. The underside of their tail is white with some black hairs near the tip. During their winter coloration, most of their body is a drab cinnamon color and their underside is silvery white. In the summer, their fur is shorter and their coloration is “browner". They molt some of their fur each year during early May and in autumn. Mohave ground squirrels are cryptically colored, meaning their fur matches their environment, making them difficult to find. When they are threatened, they often crouch and wait, blending into their surroundings. Their front feet are hairless, but their rear feet have long hairs. Their ears blend in to the rest of their head and they have white eyelids. Males and females of this species are about the same size. ("The Animal Ageing and Longevity Database", 2012; Burt, 1936; Grinnell and Dixon, 1910; Jameson and Peeters, 1988)

  • Sexual Dimorphism
  • sexes alike
  • Range mass
    85 to 130 g
    3.00 to 4.58 oz
  • Range length
    210 to 230 mm
    8.27 to 9.06 in
  • Average length
    224 mm
    8.82 in
  • Average basal metabolic rate
    0.6290 cm3.O2/g/hr

Where do they live?

Mohave ground squirrels (Spermophilus mohavensis) have a patchy distribution throughout the northwestern Mohave Desert in California. They are found in portions of Inyo, Kern, Los Angeles and San Bernardino counties. A small population of Mohave ground squirrels can also be found in the Coso Hot Springs area, about 13 kilometers northeast of Inyo county. (Grinnell and Dixon, 1910; Hafner and Yates, 1983; Harris and Leitner, 2004; Zembal and Gall, 1980)

What kind of habitat do they need?

Mohave ground squirrels occupy an area with hot, rainless summers and moderate winters, although temperatures may occasionally fall below freezing. These squirrels are most often found at elevations from 600 to 1,800 meters above sea level, in hot deserts known as the Lower Sonoran zone. Mohave ground squirrels are found in areas with 10 to 19% plant cover. They are often found in lower elevation deserts, but these squirrels can also be found in the Joshua tree belt, at elevations from 400 to 1,800 meters. Their preferred habitat seems to include sandy soil or a sandy gravel mix, with sage brushes. Mohave ground squirrels are usually found on flat, non-hilly land. They have been seen in all major scrub habitats in the western Mojave Desert. (Best, 1995; Burt, 1936; Gossard, 1992; Grinnell and Dixon, 1910; Gustafson, 1993; Zembal and Gall, 1980)

  • Range elevation
    600 to 1,800 m
    1968.50 to ft
  • Average elevation
    1,200 m
    ft

How do they reproduce?

Little is known about the reproductive behavior of Mohave ground squirrels.

Mohave ground squirrels emerge from hibernation in February; the males emerge up to two weeks before the females and begin establishing and defending territories. During the breeding season, the average male territory size is 6.7 hectares, this helps males mate with multiple females. Mating is believed to take place in the male’s burrow. The annual breeding season takes place during February and March. They have about a one month gestation period and young are generally born in late March or early April. Litters may range from 4 to 9 offspring. Females can usually begin mating at 1 year of age, while males do not begin mating until two years of age. ("The Animal Ageing and Longevity Database", 2012; Bartholomew and Hudson, 1960; Best, 1995; Burt, 1936; Harris and Leitner, 2004; Harris and Leitner, 2005; Leitner and Leitner, 1998)

  • How often does reproduction occur?
    Mohave ground squirrels breed once annually.
  • Breeding season
    Mating generally occurs during late March or early April.
  • Range number of offspring
    4 to 9
  • Average number of offspring
    6
  • Average gestation period
    30 days
  • Average weaning age
    36 days
  • Average age at sexual or reproductive maturity (female)
    1 years
  • Average age at sexual or reproductive maturity (male)
    2 minutes

Offspring are altricial at birth; they are generally blind and unable to hear, with scarce hair, found only on their heads. Young make high-pitched squeaking noises, likely associated with suckling. Litters emerge from the burrows from late April to mid May. Females continue lactating through May. During years with drought and limited resources, Mohave ground squirrels may not reproduce. This may continue for several years. Choosing not to reproduce when conditions are poor may help the animals maintain fat reserves for aestivation and hibernation. (Best, 1995; Harris and Leitner, 2005)

How long do they live?

The lifespan of wild Mohave ground squirrels is not known, but it is thought to be about 5 years or more. In captivity, they have lived up to 7.8 years. ("Basic Facts about Mohave ground squirrels", 2013; Weigl, 2005)

  • Average lifespan
    Status: wild
    5 years
  • Typical lifespan
    Status: captivity
    7.8 (high) years

How do they behave?

Mohave ground squirrels are diurnal. After emerging from their burrow in the morning, they bask in the sun, periodically rotating to warm different parts of their bodies. They feed continuously during daylight hours, from three hours after sunrise until one hour prior to sunset. They forage in shaded areas in the middle of the day, due to the extreme heat. They collect food, such as Joshua tree seeds (Yucca brevifolia), and store them in their burrow. Mohave ground squirrels make frequent trips to their burrows to stash seeds, at intervals of 15 to 20 minutes. (Best, 1995; Zembal and Gall, 1980)

Mohave ground squirrels are generally solitary. Usually only one squirrel is observed harvesting seeds from a particular Joshua trees (Yucca brevifolia) at a time. Related species, such as antelope ground squirrels are social by comparison, and are found in overlapping areas with Mohave ground squirrels. However, Mohave ground squirrels are dominant, as antelope ground squirrels have been observed retreating from them. Although solitary and very intolerant of their own species, Mohave ground squirrels are described as calm, docile and readily approached. (Bartholomew and Hudson, 1960; Zembal and Gall, 1980)

Observations of Mohave ground squirrels' activities show that they are more calm during cloudy weather than on warm, sunny days. If threatened, Mohave ground squirrels typically hold their tail over their back when running. However, they rarely run long distances, as most of their time is spent near burrows. When danger is perceived, they may also remain still, blending into their environment due to their cryptic coloration. If disturbed while feeding, Mohave ground squirrels stand on their hind legs to better survey the area. (Burt, 1936)

The entrance to Mohave ground squirrels' burrows is at a 35 degree angle. When they dig their burrow, they likely scatter the dirt. However, when squirrels entered a burrow, they plug the entrance from within using dirt and grasses. (Burt, 1936)

Mohave ground squirrels typically enter aestivation in July or September, after building up their fat reserves, when temperatures decrease to between 20 and 30 degrees Celsius and their food sources are reduced due to lack of water. This period of inactivity continues until February. During hibernation Mohave ground squirrels have reduced body temperature, reduced oxygen consumption, prolonged periods of apnea (a state of deep sleep) and are awakened by heat. (Bartholomew and Hudson, 1960)

  • Range territory size
    67,299.22 (high) m^2
  • Average territory size
    12,221.51 m^2

Home Range

Male Mohave ground squirrels have large territories, averaging 6.7 hectares, immediately after emerging from hibernation in February, probably to mate with as many females as possible. Males maintain their territories until June, at which time dominant ground squirrels take the best foraging areas. This allows the dominant individuals to occupy smaller home ranges, while juveniles may be forced to roam an area twice the size of their dominant counterparts. Home range sites and sizes are dependent on food quality, which is related to rainfall. After the mating season, the average home range size of Mohave ground squirrels is 1.24 hectares for males and 1.20 hectares for females. (Best, 1995; Harris and Leitner, 2004)

How do they communicate with each other?

Mohave ground squirrels spend much of their year in aestivation or hibernation, so little is known about their communication. These animals are generally solitary, which makes observations difficult. Even mating behavior is difficult to observe because it takes place below ground. Their call is described as a “shrill whistle.” It is a high pitched 'beep', with a slight rasping sound, similar to a horned lark. Newborn Mohave ground squirrels produce high-pitched squeaky noises, likely associated with suckling. (Best, 1995; Burt, 1936; Zembal and Gall, 1980)

What do they eat?

Mohave ground squirrels eat the seeds of Joshua trees, when they are available, they seem to be their preferred food, unfortunately, Joshua trees do not flower every year. Mohave ground squirrels harvest seeds during the day, from three hours after sunrise until one hour before sunset. These animals are larder hoarders of seeds, meaning they store them in their burrows. They are omnivorous, the majority of their diet is composed of plants as well as a smaller percentage of grasshoppers, ants and beetles. Arthropods make up 5 to 8% of Mohave ground squirrels' diet. Plants in their diet include spotted locoweed, white mallow, Arabian schismus, woolly desert marigold, desert calico, species of genus Gilia, and saltbushes. Mohave ground squirrels eat flowers, seeds and leaves. They may eat different foods at different times of the year; some plants are highly valued at certain times of year for their water content. (Best, 1995; Grinnell and Dixon, 1910; Laabs, 1998; Morton, 1979; Zembal and Gall, 1980)

  • Animal Foods
  • insects
  • Plant Foods
  • leaves
  • seeds, grains, and nuts
  • flowers
  • Other Foods
  • fungus

What eats them and how do they avoid being eaten?

The specific predators of Mohave ground squirrels are not known, however, there are many common predators in the Mohave Desert that may prey on the species, such as golden eagles, prairie falcons, red-tailed hawks, badgers, bobcats, coyotes and Mohave rattlesnakes. When they perceive danger, Mohave ground squirrels go inside their burrow, but they poke their heads out for observation. Sometimes these ground squirrels freeze in the presence of danger and wait, relying on their cryptic coloration for protection. (Burt, 1936; Gustafson, 1993)

  • These animal colors help protect them
  • cryptic

What roles do they have in the ecosystem?

Although it is not known for certain, Mohave ground squirrels may disperse Joshua tree seeds. This is based on the seed dispersal performed by their close relative, white-tailed antelope squirrels. Mohave ground squirrels are less common than the other ground squirrels found in their habitat, due to this, it is less likely that predators are dependent on them as a significant food source. Their burrows may contribute to soil aeration, based on similar practiced by round-tailed ground squirrels. There have been no reports of parasites associated with Mohave ground squirrels. (Waitman, et al., 2012)

Do they cause problems?

There are no known negative effects of Mohave ground squirrels on humans.

How do they interact with us?

There are no known positive effects of Mohave ground squirrels on humans.

Are they endangered?

Due to their limited distribution, Mohave ground squirrels are considered threatened. Major threats to this species include development, habitat fragmentation and habitat degradation. In 1971, the state of California first listed Mohave ground squirrels as rare, which led to studies about their population, however, estimating their population size is difficult because this species is inactive most of the year and they are unevenly distributed, due partly to the yearly change in food availability. So the quality of their habitat is probably the best indicator of a healthy population. In order to preserve Mohave ground squirrels, preserving large areas of land is encouraged. (Gustafson, 1993; Laabs, 1998)

Some more information...

Contributors

Caleb Eckloff (author), Northern Michigan University, John Bruggink (editor), Northern Michigan University, Leila Siciliano Martina (editor), Animal Diversity Web Staff.

References

2013. "Basic Facts about Mohave ground squirrels" (On-line). Defenders of Wildlife. Accessed May 02, 2013 at http://www.defenders.org/mohave-ground-squirrel/basic-facts.

2012. "The Animal Ageing and Longevity Database" (On-line). Human Ageing Genomic Resources. Accessed February 16, 2013 at http://genomics.senescence.info/species/entry.php?species=Spermophilus_mohavensis.

Bartholomew, G., J. Hudson. 1960. Aestivation in the Mohave ground squirrel, Citellus mohavensis. Bulletin of the Museum of Comparative Zoology, 124: 193-208.

Best, T. 1995. Spermophilus mohavensis. Mammalian Species, 509: 1-7.

Burt, W. 1936. Notes on the habits of the Mohave ground squirrel. Journal of Mammalogy, 17: 221-224.

Gossard, G. 1992. The Joshua Tree, A Controversial, Contradictory Desert Centurion. Tehachapi, CA: Yellow Rose Publications.

Grinnell, J., J. Dixon. 1910. Natural History of the Ground Squirrels of California. Monthly Bulletin of the State Commision of Horticulture, 7/11-12: 597-708. Accessed January 31, 2013 at http://archive.org/stream/naturalhistoryof00grin/naturalhistoryof00grin_djvu.txt.

Gustafson, J. 1993. A status review of the mohave ground squirrel (Spermophilus mohavensis). Nongame Bird and Mammal Section Report, 93:9: 1-234. Accessed February 10, 2013 at https://nrm.dfg.ca.gov/FileHandler.ashx?DocumentVersionID=17416.

Gustafson, J., S. Harris, R. Jones, S. Juarez, T. Moore, D. Racine, A. Tenneboe, J. Vance, T. Dayak, C. Bernis, P. Leitner, T. Recht, L. Oviatt, R. Scott, C. Wilkerson, C. Everly, S. Collis, B. Wood, M. Quillman, B. Shomo, S. Ellis, L. LaPre, B. Parker, C. Sullivan, R. McMorran, C. Gonzalez, M. Joia, T. Campbell, J. O'Gara. 2006. "Mohave Ground Squirrel Conservation Strategy" (On-line). Desert Mangers Group. Accessed March 21, 2013 at http://www.dmg.gov/documents/DFT_MGS_Consv_Strategy_DMG_082906.pdf.

Hafner, D. 1992. Speciation and persistence of a contact zone in Mohave Desert ground squirrels, subgenus Xerospermophilus. Journal of Mammalogy, 73/4: 770-778.

Hafner, D., T. Yates. 1983. Systematic status of the Mohave ground squirrel, Spermophilus mohavensis (subgenus Xeropermophius). Journal of Mammalogy, 64: 397-404.

Harris, J., P. Leitner. 2005. Long-Distance Movements of Juvenile Mohave Ground Squirrels, Spermophilus mohavensis. The Southwestern Naturalist, 50/2: 188-196.

Harris, J., P. Leitner. 2004. Home-Range Size and Use of Space by Adult Mohave Ground Squirrels, Spermophilus mohovensis. Journal of Mammalogy, 85/3: 517-523.

Jameson, E., H. Peeters. 1988. Mammals of California. Berkeley, CA: University California Press.

Krzysik, A. 1994. The mohave ground squirrel at Fort Irwin, California. USACERL Technical Report, 94/09: 1-40. Accessed March 14, 2013 at http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA299946.

Laabs, D. 1998. Mohave Ground Squirrel, Spermophilus mohavensis. Bureau of Land Management, 1: 1-7. Accessed January 31, 2013 at http://www.blm.gov/ca/pdfs/cdd_pdfs/Mgs1.pdf.

Leitner, P., B. Leitner. 1998. Coso grazing exclosure monitoring study: Mohave ground squirrel study, Coso Known Geothermal Resource Area: Major findings, 1988- 1996. Orinda, CA: CalEnergy Company, Inc..

Morton, S. 1979. Diversity of Desert-Dwelling Mammals: A Comparison of Australia and North America. Journal of Mammalogy, 60/2: 253-264.

Waitman, B., S. Vander Wall, T. Esque. 2012. Seed dispersal and seed fate in Joshua tree (Yucca brevifolia). Journal of Arid Environments, 81: 1-8.

Weigl, R. 2005. Longevity of mammals in captivity; from the Living Collections of the world. Stuttgart, Germany: Kleine Senckenberg-Reihe, Band 48.

Zembal, R., C. Gall. 1980. Observations on Mohave ground squirrels, Spermophilus mohavensis, in Inyo County, California. Journal of Mammalogy, 61: 347-350.

 
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Eckloff, C. 2013. "Spermophilus mohavensis" (On-line), Animal Diversity Web. Accessed September 01, 2014 at http://www.biokids.umich.edu/accounts/Spermophilus_mohavensis/

BioKIDS is sponsored in part by the Interagency Education Research Initiative. It is a partnership of the University of Michigan School of Education, University of Michigan Museum of Zoology, and the Detroit Public Schools. This material is based upon work supported by the National Science Foundation under Grant DRL-0628151.
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