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Overview

Brief Summary

Description

The Idaho Ground Squirrel is the only mammal endemic to Idaho. One subspecies, Spermophilus brunneus brunneus, lives only in about two dozen mountain meadows, and in 1998, biologists counted only 500 of them. Other subspecies may fare better, but the life of a ground squirrel is perilous. Only 40-60 percent of the adults survive their 8-9 month hibernation, and mortality is as high as 90 percent for juveniles. Females can mate for only a few hours a year, shortly after they emerge from hibernation. After mating (in the burrow) males guard the females from other males, which exposes the males to predation by prairie falcons and goshawks.

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  • Original description: Howell, A.H., 1928.  Descriptions of six new North American ground squirrels, p. 211.  Proceedings of the Biological Society of Washington, 41:211-214.
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Distribution

Range Description

This species is endemic to a five-county area of west-central Idaho in the United States (Yensen and Sherman 1997). The northern subspecies (brunneus) presently is known only from Valley and Adams counties at elevations of 1,150-1,550 m asl; most populations are small and often isolated by several kilometres (Yensen 1991). The southern subspecies (endemicus) has a patchy distribution at lower elevations (670-975 m asl) north of the Payette River in Gem, Payette, and Washington counties. The species is apparently extirpated in the area between the extant populations of the northern and southern subspecies (Yensen 1984, 1991, Yensen et al. 1991, Yensen and Sherman 1997). Even within subspecies, populations are disjunct.
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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: (1000-5000 square km (about 400-2000 square miles)) This species is endemic to a five-county area of west-central Idaho (Yensen and Sherman 1997). The northern subspecies (brunneus) presently is known only from Valley and Adams counties at elevations of 1,150-1,550 meters; most populations are small and often isolated by several kilometers (Yensen 1991). The southern subspecies (endemicus) has a patchy distribution at lower elevations (670-975 meters) north of the Payette River in Gem, Payette, and Washington counties. The species is apparently extirpated in the area between the extant populations of the northern and southern subspecies (Yensen 1984, 1991, Yensen et al. 1991, Yensen and Sherman 1997).

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Geographic Range

Spermophilus brunneus is found only in west-central Idaho. This area consists of five counties which have an elevation between 1150 and 1550 m.

Biogeographic Regions: nearctic (Native )

  • Gravin, T. A., P. W. Sherman, E. Yensen, B. May. 1999. Population Genetic structure of the Northern Idaho Ground Squirrel (Spermophilus brunneus brunneus). Jounal of Mammalogy, 88 (1): 156-168.
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Physical Description

Morphology

Physical Description

Spermophilus brunneus has a small head and body that is between 209 and 258 mm; the hind foot is less than 40 mm; skull length is 36.1 to 42.5 mm; ear length is 13 to 18 mm; and tail length is 39 to 65 mm. This species is sexually dimorphic, with males about 2.5% larger than females. Weight varies seasonally, and can be between 109 and 258 g.

The dorsal pelage of S. brunneus is dark reddish-gray in color, which is the result from a mixture of black unbanded, and yellowish-red banded guard hairs. It has an off-white eye ring.

Young Idaho ground squirrels do experience a diffuse molting in pelage. The molting season usually occurs in May and early June; however, adult S. brunnesus does not molt and tends to have longer pelage.

The rostrum of a S. brunneus is relatively short and these animals have a broad braincase. The dental formula of Idaho ground squirrels is i 1/1 c 0/0 p 2/1 m 3/3 = 22.

Range mass: 109 to 290 g.

Range length: 209 to 258 mm.

Sexual Dimorphism: male larger

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Size

Length: 22 cm

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Size in North America

Sexual Dimorphism: Males are slightly larger than females.

Length:
Average: "233 mm "
Range: 209-258 mm

Weight:
Range: 120-290 g
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Diagnostic Description

Differs from S. TOWNSENDII by the darker nose, legs, and under surface of the tail.

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Ecology

Habitat

Habitat and Ecology

Habitat and Ecology
It occurs in mountain meadows surrounded by forests of ponderosa pine and Douglas fir. S. b. endemicus is found in areas originally covered with sagebrush and native bunchgrasses, but the current vegetation consists of annual grasslands composed of introduced grasses.

Mating occurs soon after spring emergence; males guard sexually receptive females from other males; after mating, female excludes male from female burrow; gestation lasts about three weeks; litter size is 2-10 (average around 6-7); young are weaned in three weeks (Yensen 1991, Spahr et al. 1991).

May be limited by competition from Columbian ground squirrel (Spahr et al. 1991). Badgers and prairie falcons are the primary predators. Feeds on green vegetation, seeds. Southern populations emerge in late January or early February and cease above-ground activity in late June or early July; northern populations are active above ground from late March or early April until late July or early August (Yensen 1991). Activity is constrained by time of snow melt and vegetation desiccation.

Systems
  • Terrestrial
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Comments: Northern populations are associated with shallow rocky soils in xeric meadows surrounded by ponderosa pine and Douglas-fir forest; southern populations inhabit low rolling hills and valleys now dominated by annual grassland with relict big sagebrush and bunch grasses (Yensen et al. 1991, Yensen 1991). This squirrel may occur on slopes and rarely on ridges (Yensen 1984). It burrows extensively in shallow rocky soils, but nest burrows are located in adjacent areas with deeper (>1 meter) well-drained soils (Yensen et al. 1991).

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The habitat of Idaho ground squirrels mainly consists of meadows, dominated by grasses and broad-leaved forbs, which are mostly surrounded by coniferous forest.

Range elevation: 1150 to 1550 m.

Habitat Regions: temperate ; terrestrial

Terrestrial Biomes: savanna or grassland

  • Yensen, E. 1991. Taxonomy and distribution of the Idaho ground squirrel, Spermophilus brunneus. Journal of Mammalogy, 72: 583-600.
  • Yensen, E., P. Sherman. 1997. Spermophilus brunneus. Mammalian Species, 560: 1-5.
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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.

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Trophic Strategy

Comments: Feeds on green vegetation, seeds.

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Food Habits

Spermophilus brunneus is primarily herbivorous and its diet consists of 40 to 50 species of plants. In spite of this overall variety, only 5 to 7 species plants make up more than half of their diet. They eat grasses (Poa bulbosa, Bromus commutatus), dicot leaves (Microseris nigrescens, Lupinus), flowers, roots and bulbs and seeds (Asteraceae, Madia). Some insects may also be consumed. Ingestion of seeds apparently increases as hiberation nears. Because of hibernation, these animals must store enough fat to sustain them through the long months of winter. Weight increases throughout the growing season.

Animal Foods: insects

Plant Foods: leaves; roots and tubers; seeds, grains, and nuts

Primary Diet: herbivore (Granivore )

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Associations

Ecosystem Roles

Idaho ground squirrels serve as prey for other larger animals such as hawks, badgers, prairie falcons, and weasels.

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Predation

Predators of S. brunneus include prairie falcons, Cooper's hawks, goshawks, red-tailed hawks, northern harriers, badgers, and sometime long-tailed weasels. Idaho ground squirrels use alarm calls to warn others of predators. They are also reported to remain still when threatened, apparently because their dirt-colored backs are often undetected by predators.

Known Predators:

Anti-predator Adaptations: aposematic ; cryptic

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Known predators

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Known prey organisms

Spermophilus brunneus preys on:
Insecta

This list may not be complete but is based on published studies.
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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: 21 - 80

Comments: Based on locations mapped on a coarse scale (Yensen and Sherman 1997), this species occurs in at least few dozen distinct areas; these include at least a few hundred occupied sites. See information for subspecies brunneus and endemicus.

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Global Abundance

2500 - 100,000 individuals

Comments: Total adult population size appears to be at least several thousand individuals (Yensen 2001, USFWS 2002). See information for subspecies brunneus and endemicus.

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General Ecology

May be limited by competition from Columbian ground squirrel (Spahr et al. 1991). Badgers and prairie falcons are the primary predators.

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Life History and Behavior

Behavior

Communication and Perception

Idaho ground squirrels communicate by making high-pitched calls. These calls are usaully alarm calls that are used to warned other ground squirrels that there are pedators in the area. This type of call is used for both terrestrial and aerial predators.

In addition to accoustic communication, these small mammals use visual signals, such as body postures, tactile communication, such as nosing, butting, biting, and chasing, and chemical communication (males sniff and lick a female's genitals prior to copulation).

Communication Channels: visual ; tactile ; acoustic ; chemical

Perception Channels: visual ; acoustic

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Cyclicity

Comments: Southern populations emerge in late January or early February and cease above-ground activity in late June or early July; northern populations are active above ground from late March or early April until late July or early August (Yensen 1991). Activity is constrained by time of snow melt and vegetation dessication.

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Life Expectancy

Lifespan/Longevity

These animals are not thought to live very long. Most mortality occurs during hibernation, with 75 to 90 percent of juveniles dying. About half of adults also fail to emerge from hibernation.

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Reproduction

Mating occurs soon after spring emergence; males guard sexually receptive females from other males; after mating, female excludes male from female burrow; gestation lasts about 3 weeks; litter size is 2-10 (average around 6-7); young are weaned in 3 weeks (Yensen 1991, Spahr et al. 1991).

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Spermophilus brunneus is very unique in that it shows sexual behavior for at least 12 to 13 days before mating. The yearling males rarely breed, and the older males are polygynous.

Males first emerge from their hibernation burrows 1 to 2 weeks before females emerge. Females are sexually attractive to males for the first couple of hours on the first or second afternoon after females emerge from hibernation. The relatively early emergence of males ensures that males are awake and ready for the females when they come out from hibernation.

Newly emerged females remain near their hibernacula, where they are courted by adult males that are at least 2 years old. Receptive females are scattered around, so males have to search for them in order to mate. Searching for mates is time consuming and dangerous, because this species inhabits the open meadow. Looking for mates puts males at risk of being spotted by hawks, which are one of the major predators of these small squirrels. So, the probability of getting sexual access is low for most males.

Once a male finds a female, he will guard that female until mating occurs. Males compete for access to receptive females, and heavier males are able to displace lighter males. There are times when multiple males sequentially guard one female, and the male who guards the female the longest sires the most offspring. Copulation occurs underground so it is not observed.

There are four events which occur during mating: a male 1) follows a female closely and sniffs or licks her genitalia, then 2) accompanies her into a burrow, where 3) the pair remains for more than 5 minutes, after which 4) a copulatory plug is observed in the female's vagina. All these criteria are fulfilled in just one afternoon of the year.

Mating System: polygynandrous (promiscuous)

Idaho groung squirrels reach sexual maturity at approximately 2 years of age. Most of courtship occurs above ground right after females emerge from hibernation in the early spring. Actual copulations occur under ground.

After fertilization, a female constructs her burrow and nest. Spermophilus brunneus females produce one litter per year. The litters usually emerge in late May to early June, about 50 to 52 days after copulation. The litter size is from two to seven with an average of 5.2 young per litter. Within 2 to 3 days after the pups emerge from their natal burrows, they disperse.

Breeding interval: Idaho Ground Squirrels breed once yearly

Breeding season: Mating occurs in the early spring, when females emerge from hibernation.

Range number of offspring: 2 to 7.

Average number of offspring: 5.2.

Average age at sexual or reproductive maturity (female): 1 years.

Average age at sexual or reproductive maturity (male): approximately 2 years minutes.

Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); viviparous

Birthing happened undergroud so parental care was not observed. But based on their mating system, females likely care for the pups with little paternal care. Females provide young with milk, grooming, and protection in the burrow. The young disperse shortly after they emerge, so parental care is not lengthy.

Parental Investment: no parental involvement; altricial ; pre-fertilization (Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female); pre-independence (Protecting: Female)

  • Sherman, P. 1989. Mate guarding as paternity insurance in Idaho ground squirrels. Nature, 338: 418-420.
  • Yensen, E. 1991. Taxonomy and distribution of the Idaho ground squirrel, Spermophilus brunneus. Journal of Mammalogy, 72: 583-600.
  • Yensen, E., P. Sherman. 1997. Spermophilus brunneus. Mammalian Species, 560: 1-5.
  • Gravin, T. A., P. W. Sherman, E. Yensen, B. May. 1999. Population Genetic structure of the Northern Idaho Ground Squirrel (Spermophilus brunneus brunneus). Jounal of Mammalogy, 88 (1): 156-168.
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Conservation

Conservation Status

IUCN Red List Assessment


Red List Category
EN
Endangered

Red List Criteria
B1b(iii,iv)c(iii,iv)

Version
3.1

Year Assessed
2008

Assessor/s
Yensen, E. & NatureServe (Hammerson, G., Jefferson, J. & Cannings, S.)

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

Contributor/s

Justification
Listed as Endangered because its extent of occurrence is less than 5,000 km², its range is severely fragmented, and there is an ongoing decline in the extent and quality of its habitat, as well as the number of locations and subpopulations and number of mature individuals due to persecution and other human disturbances. This species is also subject to extreme fluctuations in the number of locations and subpopulations and number of mature individuals.

History
  • 2000
    Endangered
  • 1996
    Endangered
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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: Small range in west-central Idaho; adult population size includes several thousand adults; most populations are small; threatened primarily by habitat loss and fragmentation; ongoing conservation efforts are addressing threats.

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Spermophilus brunneus is considered to be "threatened or endangered" by the United States Fish and Wildlife Service. In 1998, 12 of the 36 populations that they studied were extinct due to loss of habitat. A study done in 1999 showed that since the populations of S. b. brunneus are small and isolated that they are prone to extinction. Apparently, the major threat to these animals is the loss of habitat due to encroaching conniferous forests.

US Federal List: threatened

CITES: no special status

IUCN Red List of Threatened Species: endangered

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Status

The Idaho ground squirrel is Endangered; the subspecies Spermophilus brunneus brunneus, the northern Idaho ground squirrel, is Critically Endangered and the subspecies S. brunneus endemicus, the southern Idaho ground squirrel, is Vulnerable.
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Population

Population
The total adult population size appears to be at least several thousand individuals (Yensen 2001, USFWS 2002). Based on locations mapped on a coarse scale (Yensen and Sherman 1997), this species occurs in at least a few dozen distinct areas; these include at least a few hundred occupied sites.

Current overall trend is uncertain but may be relatively stable. With regards to the long term trend, a significant decline has occurred in area of occupancy, number of subpopulations, and population size (USFWS 2002, 2004).

Population Trend
Decreasing
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Global Short Term Trend: Relatively stable (=10% change)

Comments: Current overall trend is uncertain but may be relatively stable. See information for subspecies brunneus and endemicus.

Global Long Term Trend: Decline of 30-70%

Comments: A significant decline has occurred in area of occupancy, number of subpopulations, and population size (USFWS 2002, 2004). See information for subspecies brunneus and endemicus.

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Threats

Major Threats
The primary threat to S. b. brunneus is loss and fragmentation of meadow habitat due to forest regrowth. Poisoning and replacement of native grasses by tall introduced grasses have also had large negative impacts on the species. Other threats include grazing by domestic livestock, off-road vehicle use (may destroy burrows), competition with Columbian ground squirrels (which may exclude S. brunneus from deeper soils that provide more favourable conditions for hibernation), and some recreational shooting (USFWS 2002). Recreational housing developments in the near future could present a major conservation challenge.

Declines of S. b. endemicus have resulted from shrub-steppe habitat conversion to agriculture, poisoning, and degradation of remaining rangeland habitat, mainly by the invasion of exotic annual grasses such as cheatgrass (Bromus tectorum) and medusahead (Taeniatherium asperum) and the loss of shrubs. This has changed the species composition of vegetation (reducing squirrel diet quality and reliability) and has altered the fire regime throughout much of the range. Recreational shooting and poisoning of ground squirrels historically were common activities, but recent regulatory changes and educational efforts probably have reduced this threat (USFWS 2004). In most areas, this squirrel faces threats associated with small population size (USFWS 2004).
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Degree of Threat: Medium

Comments: The major threat in the northern part of the range is loss and fragmentation of meadow habitat, primarily due to dense regrowth of conifers as a result of fire suppression and ecological succession following logging; but agricultural conversion, road construction, and residential and golf course development also destroy and fragment habitat (Sherman and Yensen 1994, USFWS 2000, USFWS 2002). Other threats include grazing by domestic livestock, off-road vehicle use (may destroy burrows), competition with Columbian ground squirrels (which may exclude S. brunneus from deeper soils that provide more favorable conditions for hibernation), and some recreational shooting (USFWS 2002).

In the southern part of the range, habitat deterioration appears to be a leading factor affecting the long-term persistence of this subspecies (Yensen 1999). In recent decades, invasion of exotic annuals of erratic productivity has changed the species composition of vegetation (reducing squirrel diet quality and reliability) and has altered the fire regime throughout much of the range. Recreational shooting and poisoning of ground squirrels historically were common activities, but recent regulatory changes and educational efforts probably have reduced this threat (USFWS 2004). In most areas, this squirrel faces threats associated with small population size (USFWS 2004).

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Management

Conservation Actions

Conservation Actions
Subspecies brunneus was listed as threatened on 5 April 2000 under the United States Endangered Species Act. Subspecies endemicus was listed as a Candidate for listing by USFWS (2001).

The USFWS announced a 12-month finding on a resubmitted petition to list subspecies endemicus under the ESA, and found the petition does warrant listing, but is precluded by other higher priority listing actions. It is still considered a candidate for listing (Federal Register, 27 December 2004).

Translocation and habitat improvement measures by the United States Forest Service have resulted in population increases of S. b. brunneus in the past five years.

At least a few occurrences are adequately protected. The following is needed: survey colonies for precise population numbers; protect occurrences from agricultural development; maintain natural habitat; research life history and reproductive biology.
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Management Requirements: See U.S. Forest Service et al. (1994).

Biological Research Needs: Research life history, reproductive biology, taxonomy.

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Global Protection: Few to many (1-40) occurrences appropriately protected and managed

Comments: At least a few occurrences are adequately protected from habitat destruction.

Needs: Protect occurrences from agricultural development; maintain natural habitat.

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Relevance to Humans and Ecosystems

Benefits

Economic Importance for Humans: Negative

No information could be found on the economic importance of Idaho ground squirrels.

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Economic Importance for Humans: Positive

No information could be found on the economic importance of Idaho ground squirrels.

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Wikipedia

Idaho ground squirrel

The Idaho ground squirrel (Urocitellus brunneus) is a species of the largest genus of ground squirrels. There are two subspecies, both in Idaho. They are also known as Idaho Spotted Ground Squirrel.

Description[edit]

The species has sexual dimorphism, with males being normally larger than females. Their weight ranges from 120 to 290 grams and are on average 233mm in length, though their range is 209mm to 258mm.

Behavior[edit]

They hibernate eight to nine months of the year.[2]

Northern Idaho ground squirrel (U. brunneus brunneus)[edit]

The northern Idaho ground squirrel subspecies, hereafter referred to as NIDGS, is found in Valley and Adams counties, in about two dozen isolated demes (population groups) thought to occur only at an elevations between 1,150 and 1,550 meters (3,770 and 5,090 ft). Recently, demes of NIDGS were discovered at elevations up to 2,290 meters (7,510 feet).[citation needed] The most recent numbers from the Fish and Wildlife Service suggest that 500 or less of these squirrels are in existence, however the recent discovery of squirrels at higher elevations may mean that there are indeed many more squirrels than we know of. Many areas of suitable squirrel habitat remain to be surveyed by Payette National Forest and Idaho Department of Fish and Game employees. The squirrel is currently protected by an agreement between the US Fish and Wildlife Service and private landowners, who, in exchange for federal funding, have agreed to allow the Fish and Wildlife Service to conduct conservation efforts on their land. Timber thinning and prescribed fire projects on the Payette National Forest have proven to expand some of the existing populations of Northern Idaho ground squirrels.

Southern Idaho ground squirrel (U. brunneus endemicus)[edit]

Southern Idaho ground squirrel

The southern Idaho ground squirrel can be found in an area about 30 by 70 kilometers (19 by 43 miles) extending from Emmett, Idaho, northwest to Weiser, Idaho and the surrounding area of Squaw Butte, Midvale Hill, and Henley Basin in Gem, Payette, and Washington counties.

Its range is bounded on the south by the Payette River, on the west by the Snake River and on the northeast by lava flows. Their habitat is typified by rolling hills, basins, and flats at an altitude of between 670 and 975 meters (2,198 and 3,199 ft).

As of 2004, the Southern subspecies is a candidate endangered species.

References[edit]

  1. ^ Yensen, E. & NatureServe (Hammerson, G., Jefferson, J. & Cannings, S.) (2008). Spermophilus brunneus. In: IUCN 2008. IUCN Red List of Threatened Species. Retrieved 8 January 2009.
  2. ^ Yensen, E.; Sherman, P.W. (1997). "Spermophilus brunneus". Mammalian Species (American Society of Mammalogists) 560. 
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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.

Northern and southern subspecies (U. b. brunneus and U. b. endemicus) are well differentiated morphologically, may be approaching species-level differentiation, according to Yensen (1991). Electrophoretic analyses yielded equivocal results regarding the species versus subspecies status of the northern and southern groups of populations (Gill and Yensen 1992). Thorington and Hoffmann (in Wilson and Reeder 2005) did not recognize endemicus even as a subspecies.

Populations of U. b. brunneus exhibit significant geographic genetic structure, apparently due to genetic drift in populations with small effective population size, reinforced by lack of gene flow following recent habitat fragmentation (Gavin et al. 1999).

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