A tree swallow is a small green and blue perching bird that migrates from North America to southern Central America each year. The birds typically measure 5 inches (about 13.5 cm) in length and weigh around 0.7 ounces (20 g). They primarily eat insects that are caught mid-air and roost in nests made of grass and twigs.
The feathers of an adult tree swallow are a metallic green and blue in appearance, with females having noticeably duller coloring when compared to the males. Juvenile tree swallow feathers also appear dull, with the color deepening over time with age. Both genders and all ages of tree swallows have pure white feathers on their undersides. The eyes of the bird are brown, and the legs and feet are also light-brown in appearance. The bill of the tree swallow is generally small in size and black in color.
In the spring and summer months, the tree swallow can be found in North America as far north as Alaska, Canada and Newfoundland. They are also located in California, Colorado, Nebraska, and Maryland. In the fall, the birds begin to gather in large flocks in the Gulf Coast region to migrate to Central America, the Caribbean, and as far south as Honduras. One flock can contain as many as one million tree swallows.
The tree swallow mainly eats insects, including beetles, grasshoppers, moths, and horseflies. In the winter months, fruits such as berries may also be consumed. Tree swallows hunt mid-air, catching insects with their small bills. The birds have been recorded flying as fast as 25 miles per hour (around 40 kilometers per hour).
When breeding, each tree swallow forms a pair with a bird of the opposite gender after arriving back North in the spring, with males appearing at the breeding grounds ahead of females. A nest for the eggs is constructed first by the females with twigs and grass, while the male provides collected feathers to reinforce the nest. The female lays four to seven eggs at a time and incubates them herself.
The male provides support for the female by diving and attacking possible intruders when the nest is in danger of being approached. Eggs generally take two weeks to hatch, with the female and male breeding pair working together for the length of the incubation. Once born, both the male and female will hunt to feed the baby birds.
Tree swallows live in areas with both water and tree cover, sometimes also preferring open field environments. This includes meadows, marshes, and wooded areas near lakes and streams. Deforestation and expanding new construction has displaced the tree swallow over time, but the birds have been shown to adapt to artificial nest boxes that have been placed by conservation effort workers to allow safe roosting and breeding.