Spermophilus brunneus

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 nearctic
  • native native

Habitat

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

• Habitat Regions
• temperate temperate
• terrestrial terrestrial

• Terrestrial Biomes
• savanna or grassland savanna or grassland

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.

• Other Physical Features
• endothermic endothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• male larger

Reproduction

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) 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.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• viviparous 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 altricial
• pre-fertilization
  • protecting
    • female
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female
• pre-weaning/fledging
  • provisioning
    • female
  • protecting
    • female
• pre-independence
  • protecting
    • female

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.

Behavior

Idaho ground squirrels are diurnal mammals which are active above ground for about five months before retreating to underground burrows. They live at higher elevations and usually emerge in late March or early April and remain active until late July or early August.

Spermophilus brunneus constructs three types of burrows; the nest burrow, auxiliary burrow, and the hibernation burrow. The nest burrow in which females rear their young is a complicated structure. It is 50 to 121 cm deep, has 3 to 11 openings, 2 to 13 branching tunnels, and 1 to 7 chambers. The nest is built on the well drained soil and deepest burrow.

The auxiliary burrow is a burrow that has no nest. It is shallower and is constructed far away from the nest burrows. The hibernation burrow, used for hibernating during winter, consists of a single tunnel that leads to a single nest chamber. Burrow openings are usually placed under rocks, shrubs, or fallen timber, but also occur on open meadows.

Males do not live near females or their young. Females are more social than are males, because they interact with their young. Females with young are known to give alarm calls to warn their offspring of predators.

• Key Behaviors
• terricolous
• fossorial fossorial
• diurnal diurnal
• motile motile
• hibernation hibernation
• colonial colonial

Home Range

Home range size for these animals has not been reported.

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 visual
• tactile tactile
• acoustic acoustic
• chemical chemical

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

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.

• Primary Diet
• herbivore herbivore
  • granivore granivore

• Animal Foods
• insects

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

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.

• Anti-predator Adaptations
• aposematic aposematic
• cryptic cryptic

Ecosystem Roles

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

Economic Importance for Humans: Positive

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

Economic Importance for Humans: Negative

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

Conservation Status

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.

Other Comments

There are ectoparasites of S. b. brunneus , and it included ticks, fleas and nematode eye-worms.

Additional Links

Encyclopedia of Life

Contributors

Nancy Shefferly (editor), Animal Diversity Web.

Naly Vang (author), University of Wisconsin-Stevens Point, Chris Yahnke (editor, instructor), University of Wisconsin-Stevens Point.

References

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.

Sherman, P. 1989. Mate guarding as paternity insurance in Idaho ground squirrels. Nature , 338: 418-420.

Yensen, E., P. Sherman. 1997. Spermophilus brunneus. Mammalian Species , 560: 1-5.

Yensen, E. 1991. Taxonomy and distribution of the Idaho ground squirrel, Spermophilus brunneus. Journal of Mammalogy , 72: 583-600.