About Tachycineta bicolor (Vieillot, 1808)
Tree swallow (Tachycineta bicolor (Vieillot, 1808)) measures approximately 12 to 14 cm (4.7 to 5.5 in) in length, weighs 17 to 25.5 g (0.60 to 0.90 oz), and has a wingspan ranging from 30 to 35 cm (12 to 14 in). Adult males have mostly glossy blue-green upperparts, with blackish wings and tail. Their underparts and cheek patch are white, while underwing coverts are gray-brown. Males have a black bill, dark brown eyes, and pale brown legs and feet. Females are duller in color than males, and sometimes have a brown forehead. Second-year females have brown upperparts with a variable number of blue feathers; some third-year females also retain part of this subadult plumage. A 1987 study suggests this subadult plumage likely allows younger females to explore nest sites, because resident males are usually less aggressive toward subadult females. A 2013 study found that resident females are less aggressive toward second-year female models when the models are presented separately from older females. It is still unknown why females eventually replace their subadult plumage; the change may allow males to assess female quality, as pairs mate assortatively based on plumage brightness. Juvenile tree swallows can be identified by their brown upperparts and gray-brown-washed breast. This species breeds in North America. Its breeding range reaches north to north-central Alaska and the tree line in Canada. In the eastern portion of the range, it extends south to Tennessee; in the western portion, south to California and New Mexico; and in the central portion, south to Kansas. It occasionally breeds further south in the United States. Vagrants are sometimes found in the Arctic Circle, the northern Pacific, Greenland, and Europe. The wintering range runs from California and southwestern Arizona in the west, and southeastern Virginia in the east, south along the Gulf Coast to the West Indies, Panama, and the northwestern South American coast. While migrating, tree swallows often use stop-over sites, spending an average of 57 days at these areas during autumn. They typically use one of three migratory flyways to reach their wintering range: the Western flyway, located west of the Rocky Mountains; the Central flyway, between the Rocky Mountains and the Great Lakes, stretching south into Eastern Mexico; and the Eastern flyway, east of the Great Lakes. When returning to nest, tree swallows usually do not change their breeding sites. Their breeding habitat is primarily open and wooded areas, especially those located near water. During the non-breeding season, they roost every night, preferring to rest in cane or reed beds over water. They may also roost over land, on trees, and on wires. Roosting sites are generally 100 to 150 kilometres (62 to 93 mi) apart.
