The UM Animal Diversity Web’s entry for Parus atricapillus (black-capped chickadee) says in part:
Black-capped chickadees prefer deciduous woodlands, open woods and parks, cottonwood groves, and willow thickets. They are most commonly seen near edges of wooded areas. They are a frequent visitor to backyard feeders. Black-capped chickadees nest in cavities, usually in dead trees or stumps, and are attracted to habitats with suitable nesting locations. During the winter, small flocks of black-capped chickadees can be found in dense conifer forests.
…Black-capped chickadees hop on trees (occasionally on the ground), rather than “walking.” These birds are very active during the day, and can often be seen foraging upside-down. Black-capped chickadees form monogamous pairs which usually stay together for several years. The black-capped chickadee social system has two extremes, one shown by territorial pairs during the breeding season, and the other consisting of non-breeding flocks. These are often mixed species flocks including nuthatches, woodpeckers, kinglets, brown creepers, warblers, and vireos. Black-capped chickadees perform short-distance migrations, but remain in the same general region throughout the year.
Read on for lots more including photos and chickadee calls.