Eastern bluebirds are beautiful, well-known, popular song birds that live in eastern North America. These little birds are easily recognized by the male's bright royal blue upper plumage, chest of reddish brown and white abdomen. The females is duller in color than the male, with grayer upperparts; but with an elegant look from the blue tinges to her wings. These bluebirds are the most common of the three bluebird species. Today many of the eastern bluebirds in North America nest in birdhouses intended for them on "bluebird trails." When not nesting, these birds fly in small flocks around the countryside.
Eastern bluebirds are found in eastern North America and Central America, from southern Canada to Nicaragua. There are a number living on Bermuda. They are partial migrants, the more northerly populations tending to move southwards in winter, with those further south generally remaining resident year-round in the breeding areas. These birds live in open woodlands, orchards, farmlands, and suburban areas. They prefer open land where there are scattered trees for nesting, perching and feeding.
The Eastern bluebird is a diurnal and very social bird. They sometimes gather in flocks numbering one hundred or more. They are also territorial and will defend a feeding and nesting territory around their nest site during the breeding season, as well as, in winter, a feeding territory. These birds are partially migratory, leaving their homes in the north when food becomes scarce or temperatures or other environmental conditions are unfavorable. When feeding, they often fly from their perch to the ground in order to catch a prey item such as an insect. Sometimes they use gleaning or fly catching. With good eyesight, they are able to locate small food items from distances of more than 100 feet. They fly quite low to the ground with a fast and irregular wing beat. Territorial males chase each other at fast speeds, sometimes fighting with their feet, plucking at feathers with their bills, and hitting their opponents with their wings.
These birds are monogamous, and a pair may mate with each other for more than just one season. Breeding usually occurs in April, though the season runs from February to September. A male will display at a potential nest site to attract a female, bringing nest material, going in and out of a suitable hole, then perching above it, waving his wings. He will select several nest sites, and the female may begin to build nests in different sites before choosing one and completing a nest. The cup-shaped nest is often located in an old woodpecker hole, a dead tree, or a nest box. It is made from dry grasses, weed stems and rootlets. 3 to 5 white or sky blue eggs are laid, and incubation is by the female, for around 12 to 14 days. The altricial chicks hatch within one or two days of one another and their mother broods them at this time. Both parents tend to their young, brooding them at night if it is cold. The chicks fledge at around 16 to 22 days, and are dependent on their parents for a further 3 to 4 weeks. Chicks are reproductively mature at the age of one.
Eastern bluebird numbers fell in the early 20th century as European starlings, house sparrows and other aggressive introduced species caused available nest holes to be increasingly difficult for the bluebirds to use. Other potential threats include increased use of pesticides as well as the use of metal fence posts in preference to wooden ones, decreasing the possibility of nesting holes in rotting posts.
According to the What Bird resource, the total population size of the Eastern bluebird is 10 million individuals. According to the All About Birds resource, the total breeding population of this species is 22 million birds, 86% of them spending some time in the U.S., 22% of them in Mexico, and 1% of them breeding in Canada. Overall, currently this species is classified as Least Concern (LC) on the IUCN Red List and its numbers today are increasing.
Being insectivorous, these birds affect insect populations in their range.