Competition: Effects of the Eastern Gray squirrel Invasion

Source: http://wdfw.wa.gov 

Aaron Johnston is a graduate student with the College of Forest Resources and his research is aimed at understanding the competitive interactions between Western and Eastern gray squirrel populations.  The Western gray squirrel was once common and widespread throughout the Pacific Northwest, but due to extensive habitat loss and degradation, this species was listed as a “threatened” in 1993. As the map to the left indicates, there are only three major populations of Western Gray squirrels left in the state and their numbers are constantly shrinking. Management restrictions have since been implemented around activities such as tree harvests, but conservation strategies for Western gray habitat increasingly occupied by Eastern grays is essential for species recovery.  In the hopes of discovering new methods to ensure Western gray survival, Aaron Johnston is working in conjunction with Washington Department of Fish & Wildlife to understand competition and interaction between the two species.  Three study sites have been established at: Fort Lewis Military Reservation, Klickitat County, and Willamette Valley – and “data collected thus far in research suggests exclusive use of space and some differential use of habitat between gray squirrel species” (UW SFR).  Squirrels are tracked using radio telemetry and experimental removal of Eastern gray populations “from selected sites [has been implemented] to evaluate competitive effects based on resulting behavior, use of resources, spatial partitioning and differences in reproduction and survival” (Johnston).  Ultimately, Aaron hopes to determine if patterns in Western gray resource use and survival at Fort Lewis Reservation will extend throughout the Pacific Northwest.

Recovery plan for the Western gray squirrel: http://wdfw.wa.gov/publications/00119/

Source: johnrakestraw.net

Written by Jen