The Washington ground squirrel became a candidate species in October 1999. An annual review of the species was conducted in December 2007.

Historical Status and Current Trends

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, and it now occurs at only three disjunct areas. The Oregon population is centered almost entirely on the United States Naval Weapons Systems Test Facility (Boardman Bombing Range), managed by the U.S. Navy, and the Boeing tract, state-owned lands originally leased to Boeing, Inc., and subleased to an agricultural corporation. Washington ground squirrels have been extirpated at most sites outside the bombing range and Boeing tract.

Habitat

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, are of particular importance. Washington ground squirrels occupy areas with a greater grass and forb cover than adjacent unoccupied areas, but soil type 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.

Life History

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 of the decline of the Washington ground squirrel. Because the squirrel is so closely tied to deep, silty soils, specifically Warden soils, tilling and other mechanisms involved in conversion of shrub-steppe habitats to agricultural crop production destroys the species' food source, and renders the soils, that are necessary for burrowing, unuseable and irretrievably modified. Intensive grazing reduces cover and forage, adversely affecting Washington ground squirrels. Often viewed as pests, they are subject to recreational shooting and poisoning.

Conservation Measures

The Washington ground squirrel is listed as endangered under the Oregon Endangered Species Act. The U.S. Fish and Wildlife Service is working with private agricultural landowners in Morrow county to protect a large area of Washington ground squirrel habitat.

References

Betts, B.J. 1999. Current status of Washington ground squirrels in Oregon and Washington. Northwestern Naturalist 80:35-38.