Tree swallows are small birds (about 14 cm long) with long wings and small legs and feet. They are irridescent greenish-blue on their head, shoulders and back, and white their chin, breast and belly. Tree swallows have a short black beak and dark brownish feet.
Young tree swallows look similar to adults, but they are brownish above instead of greenish blue. (Robertson, et al., 1992)
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, et al., 1992)
Tree swallows live in open areas near water, such as fields, marshes, meadows, shorelines, beaver ponds, and wooded swamps. Tree swallows need habitats with cavities for nesting. They can find these cavities in dead trees, in live trees where sapsuckers have made holes, under the eaves of buildings,and in artificial nest boxes. (Robertson, et al., 1992)
Tree swallows are socially monogamous (one male forms a breeding pair with one females). Males and females form breeding pairs as soon as the females arrive at the breeding sites in the spring. However, tree swallows often copulate with other tree swallows that are not their mates. This means that it is common for the chicks in a nest to have different fathers. (Robertson, et al., 1992)
Tree swallows breed between May and September. They raise one brood per year. Tree swallows usually nest solitarily. However, they may nest near other tree swallows if nest cavities are close together.
Tree swallows build their nests in late April or early May. Their nests are usually built in holes in dead or live trees or in hollow stumps. The female builds the nest using grasses, mosses, rootlets, and aquatic plants. She then lines it with feathers from other birds. Building the nest takes a few days to two weeks. The female lays 2 to 8 (usually 4 to 7) eggs, usually in early May. She incubates the eggs for 14 to 15 days. When the eggs hatch, the chicks are altricial (helpless). The female broods them for the first three days, and both parents feed them.
The chicks leave the nest (called fledging) at 15 to 25 days old (usually at 18 to 22 days). They are able to fly right away. The parents continue to feed the chicks for at least 3 days after they leave the nest. These chicks will be able to breed the next summer. (Robertson, et al., 1992)
Female tree swallows build the nest, incubate the eggs and brood the chicks. Both parents feed the chicks while they are in the nest and for at least three days after they fledge. (Robertson, et al., 1992)
The oldest known tree swallow lived at least 11 years. Most tree swallows probably live about 3 years. (Robertson, et al., 1992)
Tree swallows are very social. They often roost together in groups of several thousand birds during the winter and migration. However, they are very territorial during the breeding season. Males and females both defend an area around their nest against other tree swallows, and against other species of cavity nesting birds.
All tree swallows migrate south in the fall and north in the spring. They migrate during the day, often in loose flocks. At night, they roost together in large groups.
Tree swallows do not spend much time on the ground. They prefer to perch in trees or on other structures instead. They also spend much of their time in flight. To bathe, swallows swoop down over a body of water and lightly brush the water. Then they begin to fly upwards, shaking the water off. They also bathe by preening during a rainfall, using it as a shower. (Robertson, et al., 1992)
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, et al., 1992)
Tree swallows communicate using sounds and body signals. Only male tree swallows sing. They sing to let other males know where their territory is. Males and females both use calls to communicate. There are at least 14 different tree swallow calls. These are used to communicate many different messages, including distress, anxiety, pleasure and submission. They may also be used to beg for food and to attract a mate to copulate with. Body signals such as crouching and wing-fluttering are used to communicate many different messages, such as aggression or desire to copulate. (Robertson, et al., 1992)
Tree swallows mostly eat flying insects, though they also eat plant materials (about 20% of their diet). They feed in flight, searching for food in open areas above water or ground. They sometimes feed in flocks when there are a lot of insects around. Tree swallows can also catch insects on the surface of water or on other surfaces.
Swallows feed from dawn until dusk, mainly on flies, beetles and ants. However, 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, et al., 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, et al., 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 pretty common bird. They have become more common over the past 25 years. There are about 20,000,000 tree swallows in the world. Pollution and acid rain are two environmental problems that may hurt tree swallow populations in the future. (Robertson, et al., 1992)
Kari Kirschbaum (author, editor), Animal Diversity Web.
Jennifer Roof (author), University of Michigan-Ann Arbor, Marie S. Harris (author), University of Michigan-Ann Arbor.
Harrison, H. 1975. A field guide to the birds' nests: United States east of the Mississippi River. New York: Houghton Mifflin, Peterson Field Guide Series.
Robertson, R., B. Stutchbury, R. Cohen. 1992. Tree Swallow (Tachycineta bicolor). Pp. 1-28 in A Poole, P Stettenheim, F Gill, eds. The Birds of North America, Vol. 11. Philadelphia, PA: The Academy of Natural Sciences; Washington, DC: The American Ornithologists' Union.