Swallows
Tachycineta bicolor
The Tree Swallow is a graceful aerial insectivore found across the Americas, recognized by its striking iridescent blue-green upperparts and clean white underparts. These birds are highly adaptable cavity nesters, readily utilizing both natural tree hollows and artificial nest boxes. Their ability to supplement their insect diet with berries allows them to return to breeding grounds earlier in spring than many other swallow species.
Typical adult measurements.
Individuals and populations vary.
01 / The telltale details
Start with shape and behavior. Then look for the smaller details.
Adults display glossy blue or blue-green iridescent upperparts, contrasting sharply with pure white underparts.
Juveniles are dusky brown on their upperparts and often show a gray-brown wash across the chest, which distinguishes them from adults.
Adult females are generally duller than males and may have a brownish forehead or a mix of brown and iridescent blue-green on their upperparts.
Characterized by a smooth, languid flight with long glides punctuated by quick wing flaps.
02 / A place in the world
Tree Swallows inhabit open or semi-open areas, typically near water sources such as ponds, marshes, lakeshores, and meadows. They require suitable nesting cavities, which can include standing dead trees, old woodpecker holes, or human-provided nest boxes.
This species breeds across central and northern North America, extending from Alaska and Canada south to California, New Mexico, Kansas, and Tennessee. They winter along the southern U.S. coasts, the Gulf Coast, through Central America to Panama, and along the northwestern coast of South America and the West Indies.
Tree Swallows are fully migratory, undertaking diurnal migrations often in loose flocks. They are among the earliest swallows to return to their breeding grounds in spring and can linger later into the fall than other swallows.
03 / Listen a little closer
Their vocalizations include a pleasant, liquid twitter, often heard frequently around nest sites, and a contact call described as a "klweet."
04 / The life behind the feathers
Their diet primarily consists of flying insects, including flies, beetles, winged ants, mosquitoes, and spiders, especially during the summer. Uniquely among North American swallows, they also consume significant amounts of plant material, particularly berries like bayberries, which can constitute up to 20% of their annual diet.
Tree Swallows are aerial insectivores, catching prey almost exclusively on the wing. They forage individually or in groups, often skimming low over open water or ground.
The female constructs a cup-shaped nest of grasses, mosses, and rootlets within a tree cavity or nest box, lining it with feathers. She lays 2 to 8 white eggs, typically 4-6, and incubates them for 11-19 days. Both parents feed the altricial young, which fledge 15-24 days after hatching.
Outside the breeding season, Tree Swallows are highly social, forming large communal roosts that can number in the hundreds of thousands or even millions during fall migration. During breeding, they are territorial around their nest site.
One more reason to pay attention
Tree Swallows are unique among North American swallows for their ability to digest berries, allowing them to survive cold snaps when insects are scarce.
They readily use human-provided nest boxes, which has made them a subject of extensive scientific research, including a long-running study at Cornell.
Fall migratory roosts can be immense, with hundreds of thousands of individuals swirling in tornado-like columns before settling for the night.
05 / An eye for the difference
AI-assisted species research. Prepared September 2026. Details can vary across regions and populations.
