The species ranges across northern North America, living in deciduous and mixed forests, forest edges, thickets, swamps, and wooded areas in cities and suburbs. Black-capped chickadees are common throughout Pennsylvania, except for the state's southwestern and southeastern corners, where they're replaced by the similar Carolina chickadee. In late summer and fall, chickadees eat wild berries and the seeds of ragweed, goldenrod and staghorn sumac. In the fall chickadees begin storing food in bark crevices, curled leaves, clusters of pine needles, and knotholes. The birds rely on these hoards when other food becomes scarce.
Chickadees also eat suet from feeding stations and fat from dead animals.
In winter, chickadees live in flocks of six to 10 birds with one dominant pair. A flock will defend its territory against other chickadee flocks. At night chickadees roost individually in tree cavities or among dense boughs of conifers. A roosting bird tucks its head under a wing to conserve body heat. On cold nights, a chickadee's temperature drops from a normal 108oF. to about 50oF., causing the bird to enter a state of regulated hypothermia, which saves significant amounts of energy.