Tree Squirrels

Scientific Name: Genus Sciurus


Colorado is home to three kinds of tree squirrels: The rusty red fox squirrel; Abert’s squirrel, which has a striking black or salt-and-pepper gray coat and magnificent ear-tufts; and the smaller but noisier pine squirrel, or chickaree. Abert’s and fox squirrels are about the same size (up to 20 inches long and two pounds in weight), although Abert’s has longer fur and therefore looks larger. The pine squirrel is much smaller – up to 14 inches long and weighing only about nine ounces.


The fox squirrel is most familiar in streamside and urban woodlands, especially on the eastern plains. Abert's squirrel is resident of ponderosa pine forests, and the pine squirrel (or chickaree) occupies high timber.


All three tree squirrels build nests of leaves, sticks, or needles, depending on habitat. Predators of the tree squirrels vary with habits and habitat. Fox squirrels spend some time on the ground and are killed by coyotes and foxes. Magpies, hawks and snakes eat nestlings. Martens are a major predator on pine squirrels. The forest-dwelling goshawk eats Abert’s squirrels.


Fox squirrels eat fruit, nuts and buds, and bury nuts for winter (and because they are forgetful, they plant a lot of trees). Abert’s squirrel does not hoard food, but eats whatever part of its host tree, ponderosa pine, is available in season: cones and inner bark of twigs. Pine squirrels harvest and store vast quantities of cones (spruce, fir, Douglas-fir, and lodgepole pine), often beneath a feeding area.


Tree squirrels have two litters of two to five young, one litter in spring, the other in early summer. Gestation is five weeks for chickarees and up to seven weeks for their larger cousins.


By David M. Armstrong Department of Ecology & Evolutionary Biology Environmental Studies Program, University Museum of Natural History University of Colorado-Boulder

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