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: small but chunky swallow with a shallowly forked tail and broad-based triangular wings. Glides more than other swallows.
Smaller violet-green swallow has white of cheek extending behind and above the eye, and has white patches on sides of rump. Bank swallow similar to immature, but smaller and with distinct, clean-cut brown breast band, different face pattern (white behind ear), and paler brown rump.
Song: an extended series of variable chirping notes—Chrit, pleet, euree, cheet, chrit, pleet.
Status and Distribution
Common. Breeding: open areas, usually near water, including marshes, fields, and swamps. Nest: brings a few pieces of vegetation to nest cavity and often includes feathers; 2–8 eggs (May–July). Migration: in spring, arrives earlier in north than other swallows, usually mid-March–early April. Departs later than other species, peaking late September in Missouri and Virginia, lingering until late November as far north as the Great Lakes. Winter: southern United States, south through Central America and the Caribbean. Open areas near water and nearby woodlands. Vagrant: casual in Bermuda, accidental in Guyana, near Trinidad, Greenland, and England.
The breeding range is expanding southward; the population is increasing in eastern and central United States.
—From the National Geographic book Complete Birds of North America, 2006