Population status of Piute ground squirrels in the Snake River Birds of Prey National Conservaton Area, 2003

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The authors sampled Piute ground squirrels (Spermophilus mollis idahoensis) at 12 sites in the Snake River Birds of Prey National Conservation Area from January through March 2003 to determine why squirrels were not active above ground after early May 2002. No evidence was found for a population crash in 2002. Tests indicated that Piute ground squirrels had not been exposed to plague within the past year. The presence of yearlings in the population indicated that squirrels reproduced in 2002, and at least some yearlings survived the winter. Both yearling and adult squirrels appeared to be reproducing at or above normal rates in 2003. The most plausible explanation for the early disappearance of Piute ground squirrels in 2002 is that squirrels entered seasonal torpor early in response to a late spring drought in that year. In addition, the breeding chronology of squirrels appears to have shifted during the past 2 decades in response to climate change/and or habitat alteration. Shrub habitats provide a more favorable and stable environment for squirrels than grass habitats. Squirrel abundance was higher on live-trapping grids with sagebrush than on grids dominated by grass, and squirrel masses were higher at sites dominated by shrubs and Sandberg bluegrass (Poa secunda). Densities in sagebrush were within the ranges reported for earlier years, but densities in grass were lower than previously reported. Low densities at grassland sites in 2003 support other findings (Yensen et al. 1992, Van Horne et al. 1997) that drought affects squirrels more in altered grass communities than in native shrub habitats. Analyses of fecal and soil nitrogen may provide additional insights into relative habitat quality. Long-term shifts in ground squirrel breeding chronology may have implications for raptors that depend on them for food.

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ELECTRONIC FILE - Zoology