Ecology of Introduced Abert's Squirrels in Saguaro National Park - Final Report

Koprowski, John

The Catalina gray squirrel is smaller and morphologically distinct from the nearest population to the south and has likely been isolated on these mountain without congeneric competitors since the last ice age that occurred some 7,000 to 10,000 years ago. The introduced Abert's squirrel has been implicated in the decline of the uncommon native in the last half of the 20th century; however, the evidence is only anecdotal and some doubt the validity of this claim. Both species rely on the reproductive tissues of trees for survival, and the potential for ecological overlap is immense. Moreover, Abert's squirrels are known to reduce cone crops of ponderosa pine by as much as 55%, a known food source of Catalina gray squirrels. As a result, the potential for ecologically significant interactions between the species is high. The conservation status of Arizona gray squirrels is poorly understood; however, the species is considered threatened in Mexico. In 1991, Catalina gray squirrels were afforded protection as a Category 2 species in recognition of potentially precarious status and the dearth of life history information; yet to date not a single paper on the ecology of Arizona gray squirrels exists. This formal status was retained until the abolition of the category by US Fish and Wildlife Service after whcihc the Coronado National Forest considered the species to be sensitive. Both species historically occurred in higher elevations of the East Unit of Saguaro National Park, where their distribution and populations are poorly known. The impact of a potentially invasive species must be documented to assess the consequences of its presence in the forest ecosystems of Saguaro National Park.