Abundance and Habitat Associations of Washington Ground Squirrels in the Columbian Basin, Oregon

Abstract

Abstract The Washington ground squirrel (Urocitellus washingtoni) is listed as threatened in Oregon and is a species of special concern in Washington. We investigated abundance and habitat selection of the species on the Boardman Bombing Range, Morrow County, Oregon during 1996–1997. Transect surveys were used to determine relative abundance among seven vegetative types, and mark-recapture methods were used to compare density of squirrels among habitats where they were present. Transect surveys indicated highest abundance in sagebrush, followed by perennial grassland then annual grassland; and no squirrels were detected in bitterbrush or low-shrub habitats. Results from live-trapping and capture-recapture methods also indicated higher densities in sagebrush habitat. Mean maximum distance moved on trapping grids was greater for males than females for adults and juveniles alike. Macro-habitat analyses revealed a selection for areas with higher silt content (Warden soils) in soils and higher vegetative cover...