Eastern Bluebird - Life History

Life History

Eastern bluebirds are very social birds. At times they gather in flocks of a hundred or more. However, they are territorial during the breeding season and may continue to defend a feeding area throughout the winter. Mating occurs in the spring and summer months. A mature female will typically raise two broods each season. Nests are constructed in trees within abandoned woodpecker holes or other cavities that provide adequate protection (usually several feet above ground). Construction of the nest is done primarily by the female and takes approximately 10 days to complete. These nests are small, cup-like structures that are lined with grass, feathers, stems, and hairs. Each female lays 3 to 7 (average 4 to 5) light-blue or, rarely, white eggs. The female incubates the eggs, which hatch after 13 to 16 days. The young are altricial at hatching, meaning they cannot care for themselves upon hatching. The female broods the chicks for up to 7 days after hatching. Fledglings then leave the nest 15 to 20 days after hatching.

Both parents cooperate in raising the young, which they feed a diet consisting almost entirely of insects. Several studies have revealed that some young will stay around the nest to help raise another brood. Fledglings are grayish in color with a speckled breast. The blue color becomes much more prominent and the speckles on their breast disappear as they mature. Bluebirds may begin breeding the summer after they are hatched.

Eastern Bluebirds can live for 6 to 10 years. The record lifespan for a bluebird was 10 years and 5 months. However, a majority of bluebirds die within their first year of life. Starvation and freezing can threaten young bluebirds, but most threats come from other animals, including humans. Natural predators of eggs and nestlings can include eastern chipmunks, flying squirrels, American black bears, fire ants and raccoons. Bluebirds of all ages (including adults) are threatened by rat snakes, racers and American kestrels. Introduced species such as European starlings, house sparrows and domestic cats pose a major threat to bluebird nests as well, with the cat being a serious predator of adult bluebirds and the other birds being competitors for nesting sites. Non-nesting adults face predation with all native species of falcon, owl and most varieties of hawks (particularly in the Accipiter genus). When approached by a predator, male eastern bluebirds make a song-like warning cry. If a male is not present, a female will begin to sing, hoping to attract a protective male back to the territory. Both males and females will also flick their wings and warble when predators are nearby but losses are often heavy when a persistent predator finds their nest.

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