[order] Passeriformes | [family] Hirundinidae | [latin] Tachycineta bicolor | [UK] Tree Swallow | [FR] Hirondelle bicolore | [DE] Sumpfschwalbe | [ES] Golondrina Bicolor | [IT] Rondine arboricola bicolore | [NL] Boomzwaluw

Boomzwaluw determination

copyright: J. del Hoyo

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.

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.

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.

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.

This species has a large range, with an estimated global Extent of Occurrence of 12,000,000 kmē. It has a large global population estimated to be 20,000,000 individuals (Rich et al. 2003). Global population trends have not been quantified, but the species is not believed to approach the thresholds for the population decline criterion of the IUCN Red List (i.e. declining more than 30% in ten years or three generations). For these reasons, the species is evaluated as Least Concern. [conservation status from birdlife.org]

Tree swallows are primarily monogamous. However, polygyny has been documents at low rates in some populations. Breeding pairs form as soon as females arrive at breeding sites in the spring. Extra-pair copulations are common in this species; as many as 50% of nests in a given population may contain young that were not fathered by the resident male.
Tree swallows breed between May and September, and raise one brood per year. They usually nest solitarily, though they will nest near each other if existing cavities are close together. Nest building takes place in late April or early May. Nests are typically built in cavities in dead or live trees (excavated earlier by woodpeckers or other species) or in hollow stumps over water. However, they can also be found under the eaves of buildings, in steel drums, fire hydrants, holes in the ground or nest boxes. Nests are built almost entirely by the female. They are made of grasses, mosses, rootlets, and aquatic plants, and are lined with feathers from other species of birds. Construction takes from a few days to two weeks.
The female lays 2 to 8 (usually 4 to 7) eggs, at a rate of one per day. The female then incubates the eggs for 11 to 19 (usually 14 to 15) days. The female broods the altricial chicks for the first three days after hatching. Both parents share the responsibility of feeding and finding food for the chicks. Chicks fledge 15 to 25 days after hatching (usually 18 to 22 days), at which time they are good fliers. 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 if they are able to establish a nest site.

The winter range extends from southern California, southwestern Arizona, northern Mexico, the Gulf Coast and southern Baja California, Honduras, where it is very abundant in winter, Nicaragua, Costa Rica, northwestern Panama and the West Indies (mainly the northern Bahamas and Cuba, but also Jamaica, Grand Cayman, Hispaniola and Puerto Rico). The migration routes east of the Rockies are along the east coast to Central America for the east coast and Great Lakes birds; the Mississippi Basin to the Gulf Coast and Central America for Canadian prairie and mid-west birds; and along the Rockies to Mexico for populations from the eastern Rockies (Butler 1988). It occasionally winters further north, as far as Long Island and Massachusetts (Bull 1974). It is an irregular winter visitor south of Honduras, on the Pacific slope of Central America, but there are several records from South America, mainly in Colombia, Venezuela, Guyana and Trinidad. There are also supposed sightings of individuals along the western South American coast as far south as Salta, Argentina (Gochfeld et al. 1980). It occurs casually or accidentally in northern Alaska, St Lawrence Island, the Bering Sea and Greenland.