The woodchuck is the largest member of the squirrel family. It builds an extensive burrow system that, once abandoned, provides refuge for many other mammals. This is probably our best-known hibernating mammal.
The gray squirrel easily tolerates life around humans in parks and other small stands of trees where it may build huge leaf nests as well as denning in hollow trees.
One squirrel may bury hundreds or even thousands of nuts. Although many are found again, squirrels contribute heavily to the planting of new trees when unfound food caches sprout and grow.
Not native to Pennsylvania, this species was introduced when a pair escaped from captivity in 1919 around Polk, Venango County. By the time of the Pennsylvania Mammal Survey (1947–1952), scattered colonies existed in western Venango and northeastern Mercer counties. They were not known to have crossed any rivers, therefore distribution seems to be bounded on the north by French Creek, the south by Sandy Creek, and the east by the Allegheny River.
This small ground squirrel builds an extensive burrow system, with multiple entrances, where large caches of food are sometimes stored. Food may also be stored in a small hole which the chipmunk excavates and then covers. Unlike the gray squirrel that hides a single acorn in each hole, large stores may be transported in the cheeks of a chipmunk for storage at a single site. Trees are sometimes climbed in search of food.
Although they are tree squirrels, these animals also burrow and may store food underground.
Not frequently seen by people, the northern and southern flying squirrels are not easily distinguished from each other at a distance. Young flying squirrels are sometimes found on the ground, in a disoriented state, after a heavy storm.
This species is common in the woodlands of southwestern Pennsylvania but it is not frequently seen because it is active at night. The animal “flies” by spreading its limbs out to the sides and flattening the furry membranes into a sail that allows it to glide down and forward for distances of up to 40 feet.