Mammal Species of the World
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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 )
endemic to a single state or province
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).
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
Other Physical Features: endothermic ; bilateral symmetry
Length: 22 cm
Size in North America
Average: "233 mm "
Range: 209-258 mm
Range: 120-290 g
Differs from S. TOWNSENDII by the darker nose, legs, and under surface of the tail.
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
Habitat and Ecology
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.
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).
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.
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 )
Comments: Feeds on green vegetation, seeds.
Idaho ground squirrels serve as prey for other larger animals such as hawks, badgers, prairie falcons, and weasels.
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.
- prairie falcons (Falco mexicanus)
- Cooper's hawks (Accipiter cooperii)
- Northern goshawks (Accipiter gentilis)
- red-tailed hawks (Buteo jamaicensis)
- northern harriers (Circus cyaneus)
- American badgers (Taxidea taxus)
- long-tailed weasels (Mustela frenata)
Anti-predator Adaptations: aposematic ; cryptic
This list may not be complete but is based on published studies.
Known prey organisms
This list may not be complete but is based on published studies.
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.
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.
May be limited by competition from Columbian ground squirrel (Spahr et al. 1991). Badgers and prairie falcons are the primary predators.
Life History and Behavior
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 ; tactile ; acoustic ; chemical
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.
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.
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); sexual ; 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)
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).
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
IUCN Red List Assessment
Red List Category
Red List Criteria
National NatureServe Conservation Status
Rounded National Status Rank: N2 - Imperiled
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.
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).
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.
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).
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).
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.
Management Requirements: See U.S. Forest Service et al. (1994).
Biological Research Needs: Research life history, reproductive biology, taxonomy.
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.
Relevance to Humans and Ecosystems
No information could be found on the economic importance of Idaho ground squirrels.
No information could be found on the economic importance of Idaho ground squirrels.
Idaho ground squirrel
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.
They hibernate eight to nine months of the year.
Northern Idaho ground squirrel (U. brunneus brunneus)
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). 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)
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).
Names and 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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