Tachycineta bicolor
tree swallow

Tree swallows breed throughout central and northern North America. The northernmost limit of the tree swallow breeding range coincides approximately with the tree line. Tree swallows winter in southern North America, primarily in Florida, and along the Caribbean coast of Central America. (Robertson, Stutchbury, and Cohen, 1992)

Tree swallows live in open areas near water, such as fields, marshes, meadows, shorelines, beaver ponds, and wooded swamps. Because tree swallows are cavity nesters, an important habitat requirement is cavities in which to nest. These can be provided by standing dead trees, sapsucker-excavated holes in live trees, under the eaves of buildings,and in artificial nest boxes. (Robertson, Stutchbury, and Cohen, 1992)

Tree swallows are small birds (14 cm total length) with long wings and small legs and feet. They are irridescent greenish-blue above and white below on the chin, breast and belly. Tree swallows have a short black beak and dark reddish-brown or brownish-gray feet.

Juvenile tree swallows are similar in appearance to adults, but are brownish rather than greenish blue. They also have a dusky wash across their white chests. One-year-old females look very similar to adults, but have a mixture of brown and irridescent greenish-blue above. (Robertson, Stutchbury, and Cohen, 1992)

Annual adult tree swallow survival is estimated at 40 to 60%. Estimated average life span of tree swallows is 2.7 years. However, the oldest known tree swallow lived at least 11 years. (Robertson, Stutchbury, and Cohen, 1992)

Tree swallows are highly social and may form flocks of several thousand birds at nighttime roosts outside of the breeding season. However, they are strongly territorial during the breeding season. Both sexes defend an area around their nest, usually a 10 to 15 m radius, against conspecifics and other nest site competitors. Competition for nest sites is thought to be the underlying motive behind much of tree swallow behavior, including sexually selective infanticide, frequent copulation, and strong aggressive responses to nest site competitors.

Tree swallows are fully migratory. They migrate during the day, often in loose flocks, and roost together in large groups at night.

As their name suggests, tree swallows spend little time on the ground, preferring instead to perch. They spend much of their time in flight and tend to glide more than any other species of swallows. In order to bathe, swallows swoop down over water. They lightly brush the water and then begin to fly upwards, shaking the water off. They also bathe by preening extensively during rainfall, using it as a shower. (Robertson, Stutchbury, and Cohen, 1992)

Home Range

The size of tree swallow home ranges changes throughout the year. Before eggs are laid, tree swallows may travel up to 60 km to forage. However, during the incubation and nestling stages, tree swallows probably stay within about 5 km of the nest site. (Robertson, Stutchbury, and Cohen, 1992)

Tree swallows communicate primarily using sounds and physical displays. Only male tree swallows sing, apparently for the purpose of proclaiming their territory. Both sexes use calls to communicate. At least 14 different tree swallow calls have been identified. The apparent purposes of these calls range from signaling distress, anxiety, pleasure and submission to begging for food and soliciting copulation. Body signals such as crouching and wing-fluttering are used to communicate a variety of messages, including aggression and solicitation of copulation. (Robertson, Stutchbury, and Cohen, 1992)

Tree swallows primarily eat flying insects, though they also eat plant materials (about 20% of their diet). They forage in flight, in open areas above water or ground. They sometimes forage in flocks when insects are abundant. They can also glean insects from the surface of water or vertical surfaces. Swallows feed from dawn until dusk, mainly on flies, beetles and ants, though stoneflies, mayflies, caddisflies, spiders and grasshoppers are also common prey. When weather conditions are bad, tree swallows feed on vegetation, including bulrushes, bayberries, and other plants' seeds. (Robertson, Stutchbury, and Cohen, 1992)

Tree swallow eggs and nestlings are vulnerable to predation by rat snakes, raccoons, black bears, American kestrels, common grackles, American crows, northern flickers, chipmunks, weasels, deer mice and feral cats. Adults are taken in flight by black-billed magpies and raptors, including sharp-shinned hawks, American kestrels, merlins, peregrine falcons and great horned owls.

Tree swallows respond to predators by mobbing them. Large numbers of tree swallows swarm and dive-bomb the predator while giving alarm calls. (Robertson, Stutchbury, and Cohen, 1992)

Tree swallows affect the populations of the animals they eat. They also provide food for their predators. They host a number of body parasites, including blowfly larvae. (Robertson, Stutchbury, and Cohen, 1992)

There are no known adverse effects of tree swallows on humans.

Tree swallows eat many kinds of insects that humans may consider to be pests.

Tree swallows are a relatively common birds. Global populations of tree swallows have increased over the last 25 years to an estimated 20,000,000. Tree swallows readily use nesting boxes, making them a good study species for studies of the effect of pollutant on birds. PCBs and DDE have been found to be present in high levels in adults, eggs, and nestlings. It has also been found that birds in more acidic wetlands produce fewer and smaller young. These observations may suggest a possible long-term problem for tree swallows. A more pressing consideration, however, is the maintenance of dead trees, which provide nest sites for tree swallows and other cavity-dwellers. (Robertson, Stutchbury, and Cohen, 1992)