Eastern bluebird (Sialia sialis)

Also known as: azure bluebird
Synonyms: Motacilla sialis
GenusSialia (1)
SizeLength: 16 - 21 cm (2) (3)
Wingspan: 25 - 33 cm (4) (5)
Weight28 - 32 g (2) (4) (5)
Top facts

The eastern bluebird is classified as Least Concern (LC) on the IUCN Red List (1).

A small, colourful thrush, the eastern bluebird (Sialia sialis) is named for its bright blue plumage and its distribution in eastern parts of North America (3) (4). One of the continent’s most easily recognised birds (2), the male eastern bluebird is a vivid blue on the back, tail, wings and head, with a contrasting red-orange throat, breast and flanks and a white belly (2) (3) (4) (5).

The female eastern bluebird is duller than the male, with greyer upperparts, a bluish tail and wings, and paler orange on the underparts (2) (3) (4) (5). As in the male, the belly and undertail are white (4). Both male and female eastern bluebirds have a large, rounded head, a plump body, a relatively short tail and legs, and a short black bill that is slightly notched at the tip (2) (3) (4). The legs, feet and eyes are black, and there is a thin white ring around the eye (2) (3).

Juvenile eastern bluebirds have dull, brownish upperparts with whitish spots, as well as white spots and streaks on the greyish-brown breast (2) (3) (4) (5). The wings and tail are bluish, with juvenile males being brighter blue than juvenile females (2) (3).

The eastern bluebird only shows slight variations in size and appearance across its large range. Eight subspecies are recognised, but the differences between them are relatively minor, and there is much overlap (2) (3).

The eastern bluebird is quite similar in appearance to the closely related western bluebird (Sialia mexicana) and mountain bluebird (Sialia currucoides), but the male western bluebird has chestnut shoulders and a blue rather than red-orange throat, while the male mountain bluebird is lighter blue and lacks a reddish breast. The females of these species can be harder to tell apart (2) (3) (4).

The most common call of the eastern bluebird is a soft, low-pitched, melodious ‘tu-a-wee’ or ‘tura-lee’, while its song is a fairly low, short, varied series of warbles and whistles (2) (4) (5). This song is usually given by the male from a high perch or in flight, although the female may sometimes also sing if a predator is spotted near the nest (2) (4).

The eastern bluebird is found across eastern North America and into Central America, occurring from southern Canada in the north to Nicaragua in the south (2) (3) (4) (5) (6). There is also a resident population on Bermuda (2) (3) (6).

This species is a partial migrant, with more northerly populations generally moving southwards in winter, while those further south usually remain resident in the breeding areas year-round (2) (3) (5).

The eastern bluebird prefers open habitats with scattered trees and shrubs, little or no understory and only sparse ground cover (2) (3) (4). This species is likely to have originally inhabited open, frequently burned savannas, beaver ponds, open woods and forest clearings, but is now more commonly found in modified habitats such as orchards, pastures, fields, parks, gardens, golf courses, roadsides and clear-cut or burned forest (2) (4) (5).

Although it may be found in similar habitats outside of the breeding season, the eastern bluebird is often more common in wooded areas at this time of year, as these may provide a greater supply of berries and other fruits (3).

The diet of the eastern bluebird consists mostly of insects and other invertebrates, including beetles, caterpillars, grasshoppers, spiders, and occasionally earthworms and snails (3) (4) (5). It will even sometimes catch larger prey such as shrews, salamanders, lizards, snakes and frogs (2) (3) (4). In autumn and winter, the eastern bluebird becomes more dependent on small fruits and berries, such as mistletoe, blueberries, currants and honeysuckle (2) (3) (4) (5).

The eastern bluebird typically hunts from a low perch, scanning the ground for prey before dropping down from the perch to capture it (2) (3) (4) (5). It may also catch insects in the air (3) (4), and perches on bushes and trees to feed on fruits (2) (3) (4).

In winter, the eastern bluebird may form small flocks to forage (2) (5), but during the breeding season a pair will aggressively defend a territory (2), even attacking other species that might compete for nesting holes (4). Most breeding takes place in April, but the breeding season may run at any time from February to September (2).

Male eastern bluebirds display at potential nest sites to attract a female, taking nest material to a suitable hole, going in and out, and perching above it while waving the wings. However, the female alone builds the nest and incubates the eggs (4) (5). The eastern bluebird typically nests in a natural tree cavity, an abandoned woodpecker hole or an artificial nest box, in which the female constructs a loose cup of grass and pine needles, lined with fine grass, hair or feathers (2) (4) (5). In areas where nest boxes are common, a female may build a nest in each available hole, but usually ends up using only one (4).

The female eastern bluebird lays a clutch of 2 to 7 pale blue eggs (4) (5), which are incubated for around 11 to 19 days (2) (4). Both adults feed the young (2) (5), which fledge at about 17 to 21 days old (4). This species often has more than one brood each year (2) (4) (5), with the young from later broods often staying with the adults over winter, forming family groups (4) (5).

The eastern bluebird starts breeding from a year old (2) and may live for up to six or seven years in the wild, or for over ten years in captivity (2) (4). This small bird may be taken by a range of predators, including snakes, bears, raccoons, birds of prey, chipmunks, squirrels and domestic cats. Nestlings may fall victim to introduced, non-native fire ants (Solenopsis invicta), which also predate the insects on which the eastern bluebird depends (2).

In the early 20th century, the eastern bluebird underwent a dramatic population decline (3) (4) (5), with its numbers falling by as much as 90 percent (3). One of the most important factors in its decline was the introduction of species such as the house sparrow (Passer domesticus) and European starling (Sturnus vulgaris), which compete with the eastern bluebird for nest sites (2) (3) (4) (5) (7). Other potential threats have included the increased use of pesticides and a switch to using metal rather than wooden fence posts, which decreases the availability of nesting cavities in rotting posts (2) (5) (7).

On Bermuda, the breeding success of the eastern bluebird has also been affected by the loss of Bermuda or southern red cedars (Juniperus bermudiana), which has reduced the availability of nest sites on the island (2).

Despite these threats, the eastern bluebird population as a whole has rebounded in recent decades as a result of conservation efforts, and is now large, widespread and increasing (2) (3) (6). This species is also likely to have benefitted from the cutting of forests and their conversion to fields and orchards, as well as from activities that increase forest openings and reduce ground cover, such as burning and cattle grazing (2) (3).

The recovery of the eastern bluebird population is largely due to the efforts of enthusiasts who have undertaken extensive nest box programmes since the 1960s and 1970s (2) (3) (4) (5). ‘Bluebird trails’ have also been set up, in which a series of bluebird boxes are placed along particular routes (4) (7). In addition to increasing the availability of nesting sites, these programmes have also benefitted the eastern bluebird by taking measures to exclude or reduce competition with non-native species (2) (4) (5).

A number of organisations, such as the North American Bluebird Society, have been set up to promote the conservation of the eastern bluebird and other cavity-nesting birds in North America (7). Further recommended conservation measures for this vibrant small bird include controlling exotic fire ants, encouraging land owners to leave old fence posts standing, and using forestry practices that leave plenty of standing dead trees in which the eastern bluebird can nest (2).

Find out more about the eastern bluebird:

More information on bluebird conservation:

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:

  1. IUCN Red List (June, 2012)
  2. Gowaty, P.A. and Plissner, J.H. (1998) Eastern bluebird (Sialia sialis). In: Poole, A. (Ed.) The Birds of North America Online. Cornell Lab of Ornithology, Ithaca. Available at:
  3. Ritchison, G. (2000) Eastern Bluebird. Stackpole Books, Mechanicsburg, Pennsylvania.
  4. The Cornell Lab of Ornithology: All About Birds - Eastern bluebird (June, 2012)
  5. Mobley, J.A. (2009) Birds of the World. Marshall Cavendish Corporation, New York.
  6. BirdLife International - Eastern bluebird (June, 2012)
  7. North American Bluebird Society (June, 2012)