Tree Swallow

The Tree Swallow is a strikingly clean-cut swallow with an iridescent blue-green back and crisp white underparts, common across much of North America. Males show the brightest, most saturated iridescence; females and immatures can appear duller, sometimes brownish above, especially in their first year.

Unlike most swallows, which nest on cliffs, banks, or structures, Tree Swallows are cavity nesters, relying on old woodpecker holes and natural tree cavities — and readily adopting nest boxes, which has made them a favorite of backyard birders and a model species for nest-box research.

Key field marks

• Glossy blue-green (sometimes appearing steel-blue) upperparts
• Sharp white underparts extending up to the chin
• Slightly notched tail (not deeply forked)
• Small black eye set against the clean white face

Similar species

Violet-green Swallow (western range overlap) shows white patches that wrap around the face above and behind the eye and white flank patches visible from above; Tree Swallow's white stops cleanly at the eye. Barn Swallow has a deeply forked tail and orange throat, quite different from Tree Swallow's clean white underparts.

Habitat

Breeds in open or semi-open areas near water — marshes, wet meadows, lakeshores, and beaver ponds — with access to standing dead trees, old woodpecker cavities, or nest boxes for nesting.

Range

Breeds across most of Canada and the northern two-thirds of the United States. Because it can switch to eating berries when insects are scarce, Tree Swallow is one of the earliest swallows to arrive in spring and among the last to depart in fall, and some winter as far north as the southern United States.

Behavior

Highly gregarious outside the breeding season, Tree Swallows form large flocks that can number in the hundreds of thousands during migration and winter, often roosting communally in marshes.

Voice

Gives a cheerful, liquid, chattering series of notes, often rendered as a bubbly "weet, weet, weet-trit," sung frequently around the nest site.

Feeding and nesting

Feeds mainly on flying insects caught over water and fields, switching to bayberries and other fruit during cold snaps when insects are unavailable — a key adaptation allowing early spring arrival and late fall departure. Nests in a cavity lined with grass and, distinctively, large white feathers, which the birds actively collect and carry, sometimes from far away.