The Carolina chickadee was often placed in the genus Parus with most other tits, but mtDNA cytochrome b sequence data and morphology suggest that separating Poecile more adequately expresses these birds' relationships.

[3] Although it and the black-capped chickadee most likely diverged about 2.5 million years ago, the birds still hybridize in the areas where their ranges overlap.

[4] The offspring of mated pairs of hybrid chickadees suffer from lower hatching success, and a male bias sex ratio, consistent with Haldane's rule.

[5] Adults are 11.5–13 cm (4.5–5.1 in) long with a weight of 9–12 g (0.32–0.42 oz), and have a black cap and bib with white sides to the face.

Their breeding habitat is mixed or deciduous forests in the United States from New Jersey and Pennsylvania west to southern Kansas and south to Florida and Texas; there is a gap in the range at high altitudes in the Appalachian Mountains where they are replaced by their otherwise more northern relative, the black-capped chickadee.

Insects form a large part of their diet, especially in summer; seeds and berries become important in winter.

[4] Carolina chickadees are able to lower their body temperatures to induce an intentional state of hypothermia called torpor.

In extreme cold weather conditions they look for cavities where they can hide in and spend up to fifteen hours at a time in torpor.