Washington State Periodic Status Review for the Western Gray Squirrel (2016)

The western gray squirrel is one of three native tree squirrel species in Washington. It was historically distributed in low elevations from Pierce County southward to Clark County, through the Columbia River gorge, and in low to mid-elevations along the eastern Cascade Mountains from Klickitat to Okanogan counties. Current distribution in the state is now primarily limited to three geographically discrete areas: the Klickitat region (Klickitat, southern Yakima, and southwestern Skamania counties); the North Cascades (Okanogan and Chelan counties); and the southern Puget Trough (Joint Base Lewis-McChord and small areas off-base in Pierce and Thurston counties).

Although not well documented, western gray squirrels were probably once uncommon to locally common across much of their range in Washington. The species was in decline by the late 1800s and was considered rare by 1970. The first statewide population estimate was derived for the period from 1994 to 2005, with the population likely numbering between 468 and 1,405 squirrels (937 ± 50%). This included estimated population sizes of 705 squirrels in the Klickitat region, 190 squirrels in the North Cascades, and 42 squirrels in the southern Puget Trough. Populations have not been formally assessed since then, but the southern Puget Trough population has likely increased due mainly to translocations of squirrels to Joint Base Lewis-McChord (JBLM) in 2007-2012 and the North Cascades population may have been negatively impacted by several massive wildfires in 2014 and 2015. Minimal information exists to determine whether or not a major change in squirrel abundance or distribution has occurred in the Klickitat population since 2005, but some habitat alteration has occurred and has perhaps caused a corresponding change in the population.

Important known threats to western gray squirrel populations in Washington are habitat loss, degradation, and fragmentation; small population size and isolation; disease; and highway mortality. The factors most linked to habitat loss for western ground squirrels include land conversion, logging, wildfire, and fire exclusion. Climate change is both a current and potential future threat through impacts to squirrel habitat and mortality from forest fires.

Because of the species’ relatively small total population size, continuing threats, and a lack of information suggesting that any of the three populations have either reached the downlisting objectives of the recovery plan or substantially declined since 2005, it is recommended that the western gray squirrel remain a state threatened species in Washington. Ongoing surveys and an improved analysis of recent habitat change in the Klickitat and North Cascades regions will provide the information needed to better clarify current western gray squirrel population levels. This information will be available to reassess the status of the species and, if warranted, a change in legal status may be recommended at that time.