(Map may reflect historical as well as recent sightings)
The Washington ground squirrel became a candidate species in October 1999. The U.S. Fish and Wildlife Service reviews the status of this and all other candidate species annually. The last review was published in the Candidate Notice of Annual Review on November 21, 2012.
Historical Status and
The Washington ground squirrel is endemic to the Columbia Plateau, south of the Columbia River and east of the John Day River. Historically, the species was distributed over much of the shrub-steppe habitat of southeastern Washington and northeastern Oregon, but its range has contracted due to habitat loss, primarily from agricultural development. Betts (1990, 1999) resurveyed historic sites in Oregon and Washington, documenting the extirpation of many historic sites, as well as documenting range contraction in both Oregon and Washington. The Washington population occurs in Adams, Douglas, Franklin, Grant, Lincoln, and Walla Walla counties. Its range appears to have been lost in Columbia, Garfield, Spokane, and Whiteman counties. The Oregon population occurs in Gilliam, Morrow, and Umatilla counties. The largest and most densely occupied area in Oregon occurs on the Naval Weapons Systems Training Facility - Boardman, managed by the U.S. Navy, and the adjacent Boardman Conservation Area, managed by The Nature Conservancy. Washington ground squirrels were thought to be extirpated at most sites in Oregon outside this area, until recent surveys have documented a more expanded presence in the state.
The Washington ground squirrel occupies sites with sandy or silt-loam texture soils that are deep and supportive enough to accommodate its burrow structures (Betts 1990, Yensen and Sherman 2003), and where there is sufficient forage. Although the species is associated with sagebrush-grasslands of the Columbia Plateau, recent studies indicate that silty loam soils, especially those classified as Warden soils, may be the most important habitat feature. Warden soils not only have a high silt content, they are very deep, allowing for deeper burrows that maintain their structure compared to sandy or shallow soils. Warden soils occur east and south of the Columbia River.
The Washington ground squirrel spends much of its time underground. Adults emerge from hibernation between January and early March, depending on elevation and microhabitat conditions, with males emerging before females. Their active time is spent in reproduction and fattening for their six-month or longer dormancy. Adults return to their burrows by late May to early June, and juveniles return about a month later. Washington ground squirrels produce only one litter of young per year due to their limited period of activity and reproduction.
Reasons for Decline
Agricultural conversion of shrub-steppe habitat is the primary cause historically for the decline of the Washington ground squirrel. Because the squirrel is so closely tied to deep, silty soils, tilling and other mechanisms involved in conversion of shrub-steppe habitats to agricultural crop production destroys the species' food source and renders soils, that are necessary for burrowing, unusable. These soils can either be irretrievably modified or take years to recover. There are some anecdotal accounts of squirrels starting to re-occupy land enrolled in the Conservation Reserve Program, however, the ability to re-occupy an area depends on the historic and current land use of the property, as well as proximity of these areas to existing colonies.
Another reason for this species’ historic decline is persecution. Often viewed as pests, this species has also been subjected to recreational shooting and poisoning historically.
The Washington ground squirrel is listed as endangered under the Oregon Endangered Species Act and is a candidate species in Washington. The U.S. Fish and Wildlife Service is working with state fish and wildlife agencies, private agricultural landowners, and other partners to conserve and monitor the status of this species.
Betts, B.J. 1990. Geographic distribution and habitat preferences of Washington ground squirrels (Spermophilus washingtoni). Northwestern Naturalist 71:27-37.
Betts, B.J. 1999. Current status of Washington ground squirrels in Oregon and Washington. Northwestern Naturalist 80:35-38.
Yensen, E. and P.W. Sherman. 2003. Ground-dwelling squirrels of the Pacific Northwest. Boise, ID. April 28 pp. + maps.