Familiar denizens across North America, tree swallows nest in abandoned cavities in dead trees or nest boxes provided for them by admiring humans. These birds are hardier than other swallows and can feed on seeds and berries during colder months. Monotypic. Length 5.8".

Spring adult: upperparts iridescent greenish blue. Wings and tail dusky blackish, underparts entirely clean white. Lores black, ear coverts blue-black. Tail slightly forked. A few females retain brown back of immature into first spring, possibly longer. Fall adult: upperparts sometimes appear more greenish than in spring. Tertials and secondaries edged pale grayish. Immature: upperparts gray-brown, with pale grayish edges on tertials and secondaries. Underparts clean white with indistinct dusky brown wash across breast, faintest in the center. Flight: