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Spermophilus brunneus

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA CHORDATA MAMMALIA RODENTIA SCIURIDAE

Scientific Name: Spermophilus brunneus
Species Authority: (A.H. Howell, 1928)
Common Name/s:
English Idaho Ground Squirrel
Taxonomic Notes: Northern and southern subspecies (S. b. brunneus and S. b. endemicus) are well differentiated morphologically, and 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.

Assessment Information [top]

Red List Category & Criteria: Endangered B1b(iii,iv)c(iii,iv) ver 3.1
Year Published: 2008
Date Assessed: 2008-06-30
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)
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

Geographic Range [top]

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.
Countries:
Native:
United States (Idaho)
Range Map: Click here to open the map viewer and explore range.

Population [top]

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

Habitat and Ecology [top]

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

Threats [top]

Major Threat(s): 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).

Conservation Actions [top]

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.
Citation: Yensen, E. & NatureServe (Hammerson, G., Jefferson, J. & Cannings, S.) 2008. Spermophilus brunneus. In: IUCN 2013. IUCN Red List of Threatened Species. Version 2013.2. <www.iucnredlist.org>. Downloaded on 21 April 2014.
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