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Overview

Brief Summary

Description

"The Mohave Ground Squirrel occupies a relatively tiny part of the Mohave Desert and is rarely seen, since it spends more than half the year underground in a burrow. Estivation—the hot-weather equivalent of hibernation—and hibernation last from mid-summer through winter, which lets them avoid the hottest, driest, and coldest months, when the least food is available. The amount of weight gained and lost by these animals annually is remarkable. Before ""powering down,"" an individual may gain about 200 g, and then lose it all before emerging. With their large, time-sensitive energy needs, the animals are susceptible to prolonged drought, when plants produce less food. Under extreme drought conditions, Mohave Ground Squirrel may not reproduce. The squirrels are omnivorous but selective about what they eat seasonally. One of their preferred foods is the seed produced by the Joshua tree. These trees are defended against other squirrels."

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  • Original description: Merriam, C.H., 1889.  Description of a new spermophile from southern California, p. 15.  North American Fauna, 2:15-16.
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Distribution

endemic to a single state or province

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National Distribution

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

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Global Range: (5000-20,000 square km (about 2000-8000 square miles)) The Mohave ground squirrel has a patchy (discontinuous) distribution (Hafner 1992, Gustafson 1993) in the northwestern corner of the Mohave Desert, south-central California, at elevations of 610-1,800 meters (Best 1995); the range coincides with a cool mesic Wisconsinan refugium in the Mohave Desert. The species occurs in southwestern Inyo, eastern Kern, extreme northeastern Los Angeles, and northwestern San Bernardino counties (Wessman 1977, California Department of Fish and Game 1990, Best 1995); from near Palmdale in the southwest to (historically) Lucerne Valley in the southeast, and from Olancha, Coso Range, and Argus Range in the northwest and the Avawatz and Soda mountains in the northeast (Gufstason 1993). The Mojave River generally defines the extreme southeastern boundary of the range, but the species historically occurred east of the river in Lucerne Valley (Stewart 2005; see list of specimens examined by Hafner 1992). The range probably included the Antelope Valley west of Palmdale and Lancaster before widespread habitat conversion occurred there. Elevational range in the eastern foothills of the Sierra Nevada extends to around 1,700 meters. Extent of occurrence is approximately 20,000 square kilometers (Stewart 2005).

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Range Description

The Mohave ground squirrel has a patchy (discontinuous) distribution (Hafner 1992, Gustafson 1993) in the northwestern corner of the Mohave Desert, south-central California in the United States, at elevations of 610-1,800 m asl (Best 1995); the range coincides with a cool mesic Wisconsinan refugium in the Mohave Desert. It occurs in southwestern Inyo, eastern Kern, extreme northeastern Los Angeles, and northwestern San Bernardino counties (Wessman 1977, California Department of Fish and Game 1990, Best 1995); from Olancha, Inyo County, south to Victorville, San Bernardino County, and from the Tehachapi Mountains of Kern County to the Granite Mountains in San Bernardino County (Biosystems Analysis 1989). The Mojave River generally defines the extreme southeastern boundary of the range, but the species historically occurred east of the river in Lucerne Valley (Stewart 2005; see list of specimens examined by Hafner 1992). Its extent of occurrence is approximately 20,000 km² (Stewart 2005).
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Physical Description

Size

Length: 23 cm

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Size in North America

Sexual Dimorphism: None

Length:
Average: 223 mm
Range: 210-230 mm

Weight:
Range: 70-300 g
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Diagnostic Description

Spermophilus mohavensis differs from S. tereticaudus in having a flat tail (vs. rounded), with the underside white (vs. buff, drab, or cinnamon) (Ernest and Mares 1987); also, mohavensis is smaller (total length usually 210-230 mm vs. 232-266 mm) and has a shorter tail (57-72 mm vs. 81-102 mm) (Ingles 1965). In a contact zone between mohavensis and tereticaudus, the former was larger in 19 of 20 cranial measurements (e.g., mean nasal length 12.7 mm vs. 11.1 mm) (Hafner 1992).

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Type Information

Type for Xerospermophilus mohavensis
Catalog Number: USNM 186469
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Mammals
Sex/Stage: Male; Adult
Preparation: Skin; Skull
Collector(s): F. Stephens
Year Collected: 1886
Locality: Mohave River, near Rabbit Springs, about 15 mi E of Mohave River, at Hesperia (see Grinnell and Dixon 1919), San Bernardino County, California, United States, North America
  • Type: Merriam, C. H. 1889 Oct 30. North American Fauna. 2: 15.
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Ecology

Habitat

Habitat Type: Terrestrial

Comments: This ground squirrel inhabits desert areas with flat or moderately sloping topography, deep sandy or gravelly friable soils, and an abundance of annual herbaceous vegetation (may be scant during droughts). Habitats include alluvial fans where desert pavement is absent, as well as desert sink shrublands and occasionally rocky areas (Wessman 1977, Zembal and Gall 1980, Gustafson 1993, Best 1995). Habitats in order of decreasing favorability: (1) creosotebush association, (2) shadscale association, (3) alkali sink association, and (4) Joshua tree association (D. F. Williams).

Topography, soil type, shrub size and density, and plant community composition likely influence the distribution of S. mohavensis (Harris and Leitner 2005).

Harris and Leitner (2005) found that juveniles that dispersed long-distances likely traveled through habitats considered marginal for permanent occupancy (e.g., rocky or gravelly soils), over elevation changes of several hundred meters. However, several juveniles did not cross a barren playa. Apparently, unvegetated areas constitute barriers to dispersal, but rough terrain and rocky soils might be traversed if some shrub cover is available (Harris and Leitner 2005). Long-distance dispersers did not incur an elevated rate of predation (Harris and Leitner 2005).

Nests are in underground burrows, often beneath large shrubs (Leitner et al. 1995). Individuals may use several different burrows.

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Habitat and Ecology

Habitat and Ecology
This ground squirrel inhabits desert areas with deep sandy or gravelly friable soils and an abundance of annual herbaceous vegetation. Habitats include alluvial fans where desert pavement is absent. Habitats in order of decreasing favourability: (1) creosotebush association, (2) shadscale association, (3) alkali sink association, and (4) Joshua tree association. Nests are in underground burrows. Individuals may use several different burrows.

Mating occurs in February-March (Harris and Leitner 2004). Litter size is 4-6; young are born in late March or early April (Biosystems Analysis 1989). No reproduction occurs during the driest years; for example, Harris and Leitner (2004) found that no reproduction occurred at their study site when early winter precipitation (October-January) was less than 30 mm.

Populations fluctuate with environmental conditions (Leitner and Leitner 1998). Populations in marginal habitats may become extirpated during extended droughts. After the return of favourable conditions, those areas may be recolonized from adjacent areas following the resumption of reproduction and dispersal of offspring from core habitats (Gustafson 1993). Long-distance movement by juveniles might be critical for connecting local populations and recolonizing sites after local, drought-related extirpation (Harris and Leitner 2005).

Mohave ground squirrels feed on green vegetation and seeds. May also eat carrion. Remains underground August until late winter or early spring (reportedly emerges in February or March, or, according to Biosystems Analysis [1989], March in the south and May in the north). Active during the spring and summer.

Systems
  • Terrestrial
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Mojave Desert Habitat

This taxon is found in the Mojave Desert, the smallest of the four North American deserts. While the Mojave lies between the Great Basin Shrub Steppe and the Sonoran Desert, its fauna is more closely allied with the lower Colorado division of the Sonoran Desert. Dominant plants of the Mojave include Creosote Bush (Larrea tridentata), Many-fruit Saltbush (Atriplex polycarpa), Brittlebush (Encelia farinosa), Desert Holly (Atriplex hymenelytra), White Burrobush (Hymenoclea salsola), and Joshua Tree (Yucca brevifolia), the most notable endemic species in the region.

The Mojave’s warm temperate climate defines it as a distinct ecoregion. Mojave indicator species include Spiny Menodora (Menodora spinescens), Desert Senna (Cassia armata), Mojave Indigobush (Psorothamnus arborescens), and Shockley's Goldenhead (Acamptopappus shockleyi). The Mojave supports numerous species of cacti, including several endemics, such as Silver Cholla (Opuntia echinocarpa), Mojave Prickly Pear (O. erinacea), Beavertail Cactus (O. basilaris), and Cotton-top Cactus (Echinocactus polycephalus).

While the Mojave Desert is not so biologically distinct as the other desert ecoregions, distinctive endemic communities occur throughout. For example, the Kelso Dunes in the Mojave National Preserve harbor seven species of endemic insects, including the Kelso Dunes Jerusalem Cricket (Ammopelmatus kelsoensis) and the Kelso Dunes Shieldback Katydid (Eremopedes kelsoensis). The Mojave Fringe-toed Lizard (Uma Scoparia), while not endemic to the dunes, is rare elsewhere. Flowering plants also attract butterflies such as the Mojave Sooty-wing (Pholisora libya), and the widely distributed Painted Lady (Vanessa cardui).

There are a total of eight amphibian species present in the Mojave Desert all of which are anuran species: the endemic Relict Leopard Frog (Lithobates onca); the endemic Amargosa Toad (Anaxyrus nelsoni); Lowland Leopard Frog (Lithobates yavapaiensis); Red-spotted Toad (Anaxyrus punctatus); Southwestern Toad (Anaxyrus microscaphus); Great Basin Spadefoot (Spea intermontana); Great Plains Toad (Anaxyrus cognatus); and the Pacific Treefrog (Pseudacris regilla).

The native range of California’s threatened Desert Tortoise (Gopherus agassizii) includes the Mojave and Colorado Deserts. The Desert Tortoise has adapted for arid habitats by storing up to a liter of water in its urinary bladder. The following reptilian fauna are characteristic of the Mojave region in particular: Gila Monster (Heloderma suspectum NT); Western Banded Gecko (Coleonyx variegatus), Northern Desert Iguana (Dipsosaurus dorsalis), Western Chuckwalla (Sauromalus obesus), and regal horned lizard (Phrynosoma solare). Snake species include the Desert Rosy Boa (Charina trivirgata gracia), Mojave Patchnose Snake (Salvadora hexalepis mojavensis), and Mojave Rattlesnake (Crotalus scutulatus).

Endemic mammals of the ecoregion include the Mojave Ground Squirrel (Spermophilus mohavensis) and Amargosa Vole (Microtus californicus scirpensis); and the California Leaf-nosed Bat (Macrotus californicus).

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Migration

Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

These squirrels have been reported as having extremely low vagility (Hafner 1992). However, Harris and Leitner (2004) found that radio-tagged adult males in the western Mojave Desert of California made extensive movements during the mating season (mid-February to mid-March); median minimum convex polygons were much larger (6.73 hectares) than those of females (0.74 hectares). Post-mating home ranges of adult females were 0.29 to 1.90 hectares (annual medians for minimum convex polygons). Males made long movements (up to at least 1.5 kilometers) during the mating season. The maximum straight-line distance moved within days for males during the mating season (median 391 meters, range 274-1,491 meters) was greater than for the postmating season, (median 130 meters, range 46-427 meters). Maximum within-day movements by females during the mating season (median 138 meters, range 96-213 meters) did not differ significantly from postmating movements (median 205 meters, range 24-371 meters).

Furthermore, Harris and Leitner (2005) documented long-distance movements by juveniles (commonly more than 1 kilometer, up to 3.9 kilometers in females and 6.3 kilometers in males. Long-distance movement by juveniles might be critical for connecting local populations and recolonizing sites after local, drought-related extirpation (Harris and Leitner 2005).

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Trophic Strategy

Comments: The diet includes foliage, flowers, and seeds (e.g., Larrea tridentata and Yucca brevifolia) of shrubs and annual plants, as available; insects; and sometimes carrion. Particular shrub species that are patchily distributed can be an important part of the diet (Best 1995) and might contribute to the often patchy distribution of S. mohavensis (Harris and Leitner 2005). In some areas, the squirrels make extensive use of spiny hopsage (Grayia spinosa), winterfat (Krascheninnikovia lanata), and saltbush (Atriplex) when annuals are not available (Leitner and Leitner 1998).

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Population Biology

Number of Occurrences

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: 1 - 80

Comments: Stewart (2005) mapped 22 locations in which this species was captured during trapping surveys in 2002-2004 (Leitner 2005). These represent four core areas plus two additional areas in which squirrels were present at low densities (Stewart 2005).

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Global Abundance

100,000 - 1,000,000 individuals

Comments: Total adult population size is unknown but may exceed 100,000 (assuming an average density of about 1 adult per hectare (Leitner and Leitner 1989) and 430,000 hectares of occupied habitat). However, the spatial and temporal distribution of this species is highly dynamic, which makes it difficult to make a reliable estimate of overall population size.

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General Ecology

Populations fluctuate with environmental conditions (Leitner and Leitner 1998). Populations in marginal habitats may become extirpated during extended droughts. After the return of favorable conditions, those areas may be recolonized from adjacent areas following the resumption of reproduction and dispersal of offspring from core habitats (Gustafson 1993). For example, Harris and Leitner (2005) observed drought-related local extirpation from 1989 to 1992 at one study site. "Despite extensive searching for suitable habitat and trapping at several locations near the site, no nearby populations were found. Nevertheless, recolonization occurred in 1993, following 2 consecutive years of higher rainfall and ground squirrel reproduction at other sites in the region."

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Life History and Behavior

Cyclicity

Comments: Most activity of adults occurs from February through July (Bartholomew and Hudson 1960). Most individuals emerge from hibernation in early to mid-March (Leitner and Leitner 1998), but emergence as early as January occurs in the warmer portions of the range. These squirrels generally are underground from August until late winter or early spring, but estivation may begin as early as April or May during strong droughts (Leitner et al. 1995). Activity occurs during daylight hours.

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Life Expectancy

Lifespan, longevity, and ageing

Maximum longevity: 7.8 years (captivity) Observations: Record longevity in captivity is 7.8 years (Richard Weigl 2005).
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Reproduction

Mating occurs in February-March (Harris and Leitner 2004). Litter size is 4-9; young are born in late March or early April (Best 1995) and generally first appear above ground from late April to mid-May (Harris and Leitner 2005). No reproduction occurs during the driest years; for example, Harris and Leitner (2004) found that no reproduction occurred at their study site when early winter precipitation (October-January) was less than 30 mm.

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Conservation

Conservation Status

National NatureServe Conservation Status

United States

Rounded National Status Rank: N2 - Imperiled

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NatureServe Conservation Status

Rounded Global Status Rank: G2 - Imperiled

Reasons: Occurs in a portion of the Mohave Desert, California; apparently abundant and extant at several sites, but rapid urban development of parts of historical range, mining, ORV use, cultivation of habitat, livestock grazing, and post-glacial climatic changes are continuing threats.

Intrinsic Vulnerability: Moderately vulnerable

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IUCN Red List Assessment


Red List Category
VU
Vulnerable

Red List Criteria
B1ab(iii)c(iv)

Version
3.1

Year Assessed
2008

Assessor/s
Hafner, D.J. & NatureServe (Hammerson, G. & Williams, D.F.)

Reviewer/s
Amori, G. (Small Nonvolant Mammal Red List Authority) & Chanson, J. (Global Mammal Assessment Team)

Contributor/s

Justification
Listed as Vulnerable because its extent of occurrence is approximately 20,000 km², its range is severely fragmented, and there is ongoing decline in the extent and quality of its habitat. Populations also experience extreme fluctuations, partly due to the effects of drought which deters the species from breeding in some years.

History
  • 2000
    Vulnerable
  • 1996
    Vulnerable
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Status

Vulnerable.
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Global Short Term Trend: Unknown

Comments: Trend over the past 10 years or three generations has not been determined. This ground squirrel exhibits large fluctuations in local population size. Further information on overall trend is needed.

Global Long Term Trend: Relatively stable to decline of 50%

Comments: Recent survey/monitoring data reveal that over twenty percent of the historical range of this species is no longer occupied (Stewart 2005).

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Population

Population
This species is rare throughout much of its range. Significant population declines have been recorded across most of the range between 1980 and 2000, and this decline is not correlated with winter rainfall, which generally increased between 1984 and 1998 (Leitner 2001, Brooks and Matchett 2002). Hafner (1992) hypothesized that low dispersal ability might be one of several possible explanations for the persistence of a stable contact zone between S. mohavensis and S. tereticaudus, the species is relatively mobile compared to other ground squirrel species. Harris and Leitner (2004) found that the size of female home ranges in years of no reproduction appears to vary in response to food availability, and that alternating size of the home range may be an adaptive response to an arid, variable environment.

Total adult population size is unknown but may exceed 100,000 (assuming an average density of about one adult per hectare (Leitner and Leitner 1998) and 430,000 hectares of occupied habitat). However, the spatial and temporal distribution of this species is highly dynamic, which makes it difficult to make a reliable estimate of overall population size.

Stewart (2005) mapped 22 locations in which this species was captured during trapping surveys in 2002-2004 (Leitner 2005). These represent four core areas plus two additional areas in which squirrels are present at low densities (Stewart 2005).

This ground squirrel exhibits large fluctuations in local population size. Further information on overall trend is needed.
Recent monitoring data reveal that over twenty percent of the historical range of this species is no longer occupied (Stewart 2005).

Population Trend
Decreasing
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Threats

Degree of Threat: C : Not very threatened throughout its range, communities often provide natural resources that when exploited alter the composition and structure over the short-term, or communities are self-protecting because they are unsuitable for other uses

Comments: The primary cause of the decline is loss and degradation of habitat caused by urbanization, agriculture, military activities, and other human uses (Gustafson 1993), including livestock grazing (and associated expansion of non-native annual grasses), off-highway vehicle use, energy production, and transportation infrastructure (California Department of Fish and Game 1990, Stewart 2005). Over 78 percent of the habitat within the species' range is either naturally unavailable, severely degraded, or is in a land-use category that represents a threat to the ground squirrel; the remainder is under threat from continued development and habitat fragmentation (Stewart 2005). The planned Fort Irwin expansion would fragment one of four remaining populations that appear to be stable, posing a serious threat to the species' persistence (Stewart 2005). Current regulatory mechanisms are believed to be inadequate to protect this species (Stewart 2005).

The effects of extended drought or other unfavorable climate change, which may extirpate local populations (Gustafson 1993), may be exacerbated by habitat loss, degradation, and fragmentation that isolate populations and reduce the probability of recolonization of depopulated habitats.

Spermophilus tereticaudus may be expanding its range at the expense of S. mohavensis (Wessman, in Hafner 1992).

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Major Threats
The primary cause of the decline is the conversion of habitat to urban, suburban, agricultural, military, and other human uses (Gustafson 1993), including livestock grazing, off-highway vehicle use, energy production, and transportation infrastructure (California Department of Fish and Game 1990, Stewart 2005). Over 78% of the habitat within the species' range is either naturally unavailable, severely degraded, or is in a land-use category that represents a threat to the ground squirrel; the remainder is under threat from continued development and habitat fragmentation (Stewart 2005). The planned Fort Irwin expansion would fragment one of four remaining populations that appear to be stable, posing a serious threat to the species' persistence (Stewart 2005). Current regulatory mechanisms are believed to be inadequate to protect this species (Stewart 2005). Spermophilus tereticaudus may be expanding its range at the expense of S. mohavensis (Wessman, in Hafner 1992).

S. mohavensis fails to reproduce during years of drought rather than risking a delay in accumulating fat reserves for aestivation. Periods of prolonged drought therefore is a potential threat to the population. The taxon exists as isolated populations with a scattered distribution. Recruitment from neighbouring colonies is thought to be rare (Hafner et al. 1998).
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Management

Preserve Selection and Design Considerations: Gustafson (1993) determined that the minimum preserve size for this species should be at least 24,290 hectares of suitable habitat. Ideally, the distance between preserves or occupied habitat patches should not exceed the dispersal capabilities of the species (see mobility/migration comments).

Management Requirements: Beneficial management includes elimination of excessive grazing and exclusion of off-road vehicles. See California Department of Fish and Game (1990) for general management recommendations.

Biological Research Needs: Better information is needed on reproduction, dispersal, demography, food habits, habitat needs, and the effects of fire, grazing, and ORV use. See California Department of Fish and Game (1990) for general research recommendations.

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Global Protection: Many (13-40) occurrences appropriately protected and managed

Comments: Only 9 percent of the suitable habitat within the historical range exists in a protected state. Stewart (2005) determined that this species occurs on a large number of protected areas (federal wilderness areas, state parks, state ecological reserves, etc.) on lands encompassing about 1,800 square kilometers. Nearly two-thirds of the range is in federal ownership (Stewart 2005).

Needs: Habitat needs to be protected from development and excessive grazing. ORV traffic should be restricted or eliminated at inhabited sites. Consideration of this species in federal land use decisions should be promoted.

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Conservation Actions

Conservation Actions
Only 9% of the suitable habitat within the historical range exists in a protected state. Stewart (2005) determined that this species occurs on a large number of protected areas (federal wilderness areas, state parks, state ecological reserves, etc.) on lands encompassing about 1,800 km². Nearly two-thirds of the range is in federal ownership (Stewart 2005).

Habitat needs to be protected from development and excessive grazing. Off-road vehicle traffic should be restricted or eliminated at inhabited sites. Consideration of this species in federal land use decisions should be promoted.

Obtain data on reproduction, dispersal, demography, food habits, habitat needs, and the effects of fire, grazing, and off-road vehicle use.
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Wikipedia

Mohave ground squirrel

The Mohave ground squirrel (Xerospermophilus mohavensis) is a species of ground squirrel found only in the Mojave Desert in California.[1] The squirrel was discovered in 1886 by Frank Stephens of San Diego (after whom the Stephens Soft-Haired Ground Squirrel is named.[2] It is listed as a threatened species under the California Endangered Species Act, but not under the federal Endangered Species Act. The IUCN lists this species as vulnerable.

The Mojave ground squirrel measures about nine inches from nose to tail and feeds on leaves and seeds from February to July. Near the end of July, the squirrels begin a period of estivation, but this may occur as early as April in drought years. Litters do not survive if drought years force an early hibernation. Local populations can be wiped out if a drought lasts for multiple years.[3]

This squirrel inhabits the western Mojave Desert in portions of Inyo, Kern, Los Angeles, and San Bernardino counties. It can occupy Joshua tree woodlands, creosote scrub, saltbush scrub and mojave mixed woody scrub. Typical forage plants are those that meet nutritional and water content requirements. These can include shrubs such as winterfat, spiny hopsage, and boxthorn (Lycium spp.). Preferred annuals include Coreopsis spp., Eremalche spp., Astragulus spp., and lupine.

Soils are usually friable and conducive to burrow excavation. Areas of preferred habitat include habitat types that provide ample forage to allow Mohave ground squirrels to persist during drought periods. These persistent populations may act as core areas from which populations expand from during adequate rainfall years which are required for Mohave ground squirrels to reproduce. This dynamic expansion and contraction in populations can make it challenging to determine whether the species is present since extended periods of drought can cause a die-off on local populations until surrounding populations expand during consecutive reproductive years.

Mohave ground squirrels emit a high-pitched "peep" as an alarm call, when startled or when young begin to emerge from their natal burrows. The vocalization is sometimes confused with that of the Horned Lark. Mohave ground squirrels can occasionally be sighted perched in Lycium cooperii or in Creosote bush (Larrea tridentata) during mid-morning (9-11 a.m.) hours (April–June) basking in the sun.

Males emerge from hibernation in early February and females are soon to follow. Reproduction occurs in early March and gestation lasts for about four weeks. Litters range from 4-6 individuals. Juveniles emerge from the natal burrows in late May to Mid June. Predators include badgers, coyotes, snakes, falcons and hawks.

References[edit]

  1. ^ a b Hafner, D. J., Hammerson, G. & Williams, D. F. (2008). Spermophilus mohavensis. In: IUCN 2008. IUCN Red List of Threatened Species. Retrieved 8 January 2009.
  2. ^ Natural History of the Ground Squirrels of California P. 667. 
  3. ^ "Tortoise Tracks". 
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Names and Taxonomy

Taxonomy

Comments: Recent molecular phylogenetic studies suggest that the traditionally recognized genera Marmota (marmots), Cynomys (prairie dogs), and Ammospermophilus (antelope ground squirrels) render Spermophilus paraphyletic, potentially suggesting that multiple generic-level lineages should be credited within Spermophilus (Helgen et al. 2009). As a result, ground squirrels formerly allocated to the genus Spermophilus (sensu Thorington and Hoffman, in Wilson and Reeder 2005) are now classified in 8 genera (Notocitellus, Otospermophilus, Callospermophilus, Ictidomys, Poliocitellus, Xerospermophilus, and Urocitellus). Spermophilus sensu stricto is restricted to Eurasia.

Xerospermohilus mohavensis and X. tereticaudus hybridize along a small, narrow, stable contact zone (Helendale, Coyote Dry Lake) that coincides with a Wisconsinan pluvial barrier; the two taxa exhibit a consistent difference in diploid number (Hafner and Yates 1983, Hafner 1992).

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