The northern flying squirrel, now declared threatened in Pennsylvania, is a habitat specialist that is closely tied to conifer forests, which in Pennsylvania, include red spruce, balsam fir, and eastern hemlock. Mature forest stands allow efficient locomotion via gliding, suitable numbers of nesting cavities, and the production of unique dietary items including hypogeous fungi and arboreal lichens. The two subspecies of northern flying squirrel found south of Pennsylvania consist of several small, disjunct populations and were listed in 1971 as federally endangered under the Endangered Species Act.