Washington Ground Squirrel Surveys in Adams, Douglas, and Grant Counties, Washington, 2004

The Washington ground squirrel (Spermophilus washingtoni) occurs in grassland and shrubland habitats of the Columbia Plateau east and south of the Columbia River in Washington and Oregon. Though it is a federal candidate for listing as threatened or endangered under the U.S. Endangered Species Act, relatively little knowledge concerning the species exists for Washington.

In its Heritage database, the Washington Department of Fish and Wildlife (WDFW) maintains a listing of Washington ground squirrel locations in the state dating back to 1941. We surveyed ground squirrel sites identified in this database for Adams, Douglas, and Grant counties, Washington, to (1) confirm species presence, (2) describe the geographic extent of active sites, (3) estimate burrow abundance at active sites, and (4) document predator activity. Our primary goal was to determine the activity status of as many historical Washington ground squirrel sites as possible to update the Heritage database and to prepare for predictive modeling of the speciesf occurrence using a Geographic Information System.

We surveyed a total of 303 Washington ground squirrel sites from late March to early June 2004 and confirmed occupancy at 218 of 247 (88%) sites that were classified as occupied during surveys conducted from 2001-2003. Occupancy rates for subregions of Washington ground squirrel sites typically exceeded 85%. However, the Seep Lakes Area in Grant County, the Hatton Area in Adams County, and the Foster Coulee Area in Douglas County each showed declines of >35% in occupancy rates from 2001-2003 to 2004. The reduction in the Seep Lakes Area exceeded the findings of Dr. Paul Sherman, who observed a 17% decline in active sites in this area from 1999 to 2001. The Black Rock Coulee and Sagebrush Flats Areas in Grant County experienced 15% and 11% declines in active sites from 2001-2003 to 2004, respectively. Nine previously undocumented sites were discovered in 2004.

Most (67.5%, n = 156) active Washington ground squirrel sites in 2004 were characterized by small estimates of burrow numbers (i.e., 1-50 burrows), with 17.7% (n = 41) of sites containing an estimated 51-100 burrows, 14.3% of sites (n = 33) having >100 burrows, and 0.4% (n = 1) of sites having an undetermined number of burrows. Areas predominated by small sites were the Foster Coulee, Duffy Creek, Saddle Mountains, Beezley Hills, and Sagebrush Flats Areas, whereas the Warden, Moses Coulee, Lind, Soap Lake, and Seep Lakes Areas contained relatively more large sites. The Warden Area had by far the largest mean estimate of burrow numbers per site, followed by the Moses Coulee, Soap Lake, and Smyrna Bench Areas. Thirtyone (93.9%) of 33 large sites occurred in Grant County, with the greatest number (n = 10) present in the Moses Coulee Area. Eighty-six (37.2%) of the 231 active sites occurred on federal land, 69 (29.9%) were on private land, 37 (16.0%) were on Nature Conservancy land, 37 (16.0%) were on WDFW and other state land, and 2 (0.9%) were on local school district land.

Biases in counting burrows and documenting sites means that some of our findings should be interpreted with caution. We identified eight areas (Seep Lakes, Hatton, Foster Coulee, Soap Lake, Warden, Ritzville, Lind, and Duffy Creek) where conservation concerns may be greatest for Washington ground squirrels. Recommendations for improved survey methodologies are provided for future work.