Current status of the western gray squirrel population in the Puget Trough, Washington
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The Puget Trough population of Washington's state-threatened western gray squirrel (Sciurus griseus) is centred in Oregon white oak (Quercus garryana) ecotones adjacent to conifer forests and prairies on the Fort Lewis Military Reservation. Our goal was to determine the current status of western gray squirrels in this region. In 1998, we found five western gray squirrels in 538 h of foot surveys in 133 oak sites. In 1999, we expanded our survey effort and included surveys on foot, surveys with simulated squirrel calls, live trapping, and bait stations with motion-sensitive cameras. No western gray squirrels were detected in any oak sites in 1999. One western gray squirrel was photographed in a ponderosa pine (Pinus ponderosa) stand adjacent to oaks. The western gray squirrel population on Fort Lewis appears to have declined severely since low population numbers were reported in 1992-93. Our ability to formulate mutually exclusive hypotheses underlying the decline of the western gray squirrel on Fort Lewis is limited by our lack of understanding of how these squirrels persist in highly-fragmented oak ecotones. Without intervention, however, the continued existence of this species in the Puget Trough may be doubtful.