The eastern bluebird (Sialia sialis) is a small North American migratory thrush found in open woodlands, farmlands, and orchards.

The bright-blue breeding plumage of the male, easily observed on a wire or open perch, makes this species a favorite of birders. The male's call includes sometimes soft warbles of ' or ', or the melodious song '.

Taxonomy

The eastern bluebird was formally described by the Swedish naturalist Carl Linnaeus in 1758 in the tenth edition of his Systema Naturae under the binomial name Motacilla sialis. The type location is South Carolina. Linnaeus based his short Latin description on the earlier more detailed descriptions by the English naturalists Mark Catesby and George Edwards. The eastern bluebird is now placed in the genus Sialia that was introduced by the English naturalist William Swainson in 1827 with the eastern bluebird as the type species.

Seven subspecies are recognized: as well as range expansions of many other species of birds. From 1966–2015 the eastern bluebird experienced a greater than 1.5% annual population increase throughout most of its breeding and year-round ranges, with exceptions including southern Florida and the Ohio River valley.

Bluebirds tend to live in open country around trees, but with little understory and sparse ground cover. Original habitats probably included open, frequently burned pine savannas, beaver ponds, mature but open woods, and forest openings. Today, they are most common along pastures, agricultural fields, suburban parks, backyards, and even golf courses. Populations also occur across eastern North America and south as far as Nicaragua. Birds that live farther north and in the west of the range tend to lay more eggs than eastern and southern birds.

Behavior and ecology

Eastern bluebirds are social, and will sometimes gather in flocks of over a hundred. However, they are territorial during the breeding season and may continue to defend a feeding area throughout the winter.

Breeding

right|thumb|Eggs

Mating occurs in the spring and summer. A mature female typically raises 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 around 10 days to complete. These nests are small, cup-like structures lined with grass, feathers, stems, and hairs. Each female lays three to seven light-blue or, rarely, white eggs. The female incubates the eggs, which hatch after 13 to 16 days. The young cannot care for themselves upon hatching. The female broods the chicks for up to seven days after hatching. Fledglings then leave the nest 15 to 20 days after hatching. It is believed that bluebirds were most abundant around 1900. Throughout the early to mid-20th century, bluebird populations suffered a major decline. The main drivers of this decline were changes in land use, clearing land for agricultural purposes, expansion of human settlements, and resources. This involved intensive logging and the destruction of their habitat and clearing dead trees, which interfered with the bird's breeding habits. DDT also contributed to the decline via contaminated insects in the bluebird's diet, which led to eggs with weakened shells that could break during incubation.

Some organisations have attributed the decline of bluebirds due to competition with introduced house sparrows and European starlings mainly owing to their aggressive nesting habits. A definite drop has been shown to have occurred between 1938 and the late 1970s. and John Burrough's "The Bluebird".

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File:Eastern Bluebird (Sialia sialis bermudensis) in Bermuda, from below.jpg|Young Eastern Bluebird (Sialia sialis bermudensis) in Bermuda, seen from below.

File:Juvenile Eastern Bluebird (Sialia sialis bermudensis) at Prospect Camp Protestant Cemetery, Bermuda.jpg|Juvenile Eastern Bluebird (Sialia sialis bermudensis) at Prospect Camp Protestant Cemetery, in Devonshire Parish in the British Overseas Territory of Bermuda.

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See also

  • Bluebird of happiness

References

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  • North American Bluebird Society
  • Life Histories of Familiar North American Birds: Eastern Bluebird
  • Eastern Bluebird Overview, All About Birds – Cornell Lab of Ornithology
  • Eastern Bluebird at Northern Prairie Wildlife Research Center
  • Bermuda Department of Conservation Services Bluebird Page
  • Sialis.org — Resources and advice for bluebird conservation.
  • Eastern Bluebird – Sialia sialis – USGS Patuxent Bird Identification InfoCenter