Sialia sialis
eastern bluebird

This species has a very broad range. It is found east of the Rocky Mountains, spanning from southern Canada to the Gulf states and on into Mexico and Honduras. There are also populations found in Cuba, although it is not a native species there. (Terres, 1980)

Eastern bluebirds prefer open land with scattered trees for perching, nesting, and feeding. They are often seen in parks, gardens, hedges, and other areas that provide perches. They are also commonly found sitting on fences and utility wires. (Terres, 1980)

Eastern bluebirds are small birds with short, slender beaks and short legs. They are brightly colored, with a blue upper body, red breast, and white abdomen. Males have wing and tail feathers that are blue with black or gray shafts and tips. Their heads are a lighter shade of blue, which fades into a red throat and breast area. The breast and belly are white with light blue tips on some of the longer feathers. Females also exhibit this pattern of coloration, although they tend to be duller than males and have more gray. Adult weight ranges from 27 to 34 grams. They are, on average 18 cm long from the tip of their beak to the end of their tail.

Young bluebirds are grayish in color. They have speckled breasts and their wings are tipped in blue. The blue color becomes much more prominent and the speckles on their breast disappear as they become adults.

There are eight recognized subspecies of Sialia sialis. These subspecies are distinguished based on coloration and geographic range. (Terres, 1980)

Eastern bluebirds are generally monogamous. However, some studies have shown that more than one female or male are involved in some broods, suggesting that monogamy is not always the rule in this species. Occasionally, juveniles of a first brood remain near the nest to help the parents raise a second brood. This behavior is uncommon among eastern bluebird. Juvenile helpers are much more common among western bluebirds. (Gowaty and Plissner, 1998)

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. Fledglings leave the nest 15 to 20 days after hatching. Several studies have revealed that some young will stay around the nest to help raise another brood.

Both parents cooperate in raising the young, which they feed a diet insects. 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. (North American Bluebird Society, 1999; Tveten, 1993)

The young are altricial, meaning they cannot care for themselves upon hatching. Both parents cooperate in raising the young. The female broods the chicks for up to 7 days after hatching. Both parents feed the chicks while they are in the nest and for about three weeks after they have left the nest. The chicks are fed mainly insects. (Gowaty and Plissner, 1998)

Eastern bluebirds can live up to 6 to 10 years. The oldest known wild individual lived 10 years and 5 months. However, most mortality occurs in the first year of life, making average lifespans much shorter than this.

Eastern bluebirds are very social. At times they gather in flocks of 100 hundred or more. However, they are territorial as well. They defend a nesting and feeding territory around their nest during the breeding season, and a feeding territory in the winter.

Eastern bluebirds are partially migratory. They leave their northern homes when food sources become scarce or when temperatures and other environmental conditions are not suitable. When feeding, bluebirds often fly from a perch to the ground to catch an insect or other prey item. Flying speeds of this bird have been measured at 17 miles per hour.

Home ranges of eastern bluebirds range from 1.1 ha (during the breeding season) to 120.8 ha (during winter). (Gowaty and Plissner, 1998)

Eastern bluebirds communicate primarily through sounds. One of the most distinguishing characteristics of this species, aside from its distinctive coloring, is its song. Bluebirds have different songs for mating, territoriality, and other purposes. When heard, the most common call of the bluebird sounds like -chir wi- or -chur lee-. When repeated several times, the call resembles the words -truly- and -purity-. Eastern bluebirds also use visual cues to communicate. (Terres, 1980; Tveten, 1993)

Eastern bluebirds eat a variety of foods depending on the season. In summer months, eastern bluebirds consume mostly beetles (order Coleoptera), crickets, caterpillars, grasshoppers, and other insects. A United States Biological Survey study of 855 eastern bluebirds found that the bluebird diet was 68% insects. During the fall and winter seasons, when insects are less common, eastern bluebirds eat fruits and plants, including blackberries, honeysuckle, dogwood, red cedar, and wild grapes.

Eastern bluebirds drink water from ponds, streams and birdbaths. They appear to prefer running water versus standing water. (North American Bluebird Society, 1999; USGS Northern Prairie Wildlife Research Center, 1999)

Eastern chipmunks and flying squirrels prey on eastern bluebird eggs and nestlings. House sparrows, European starlings, American kestrels black rat snakes, black racers, fire ants, domestic cats, black bears, and raccoons are predators of adults and chicks.

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. (Gowaty and Plissner, 1998)

Eastern bluebirds influence the composition of insect communities through their predation on insects. They also host many species of parasites, including mites, lice and blowflies.

Eastern bluebirds affect communities of the insects they eat. They also provide habitat for many species of parasites, including mites, lice and blowflies.

Eastern bluebirds may help to control insect populations.

There are no known adverse affects of eastern bluebirds on humans.

The future of eastern bluebirds has been of concern to conservation agencies. Population numbers have dropped drastically in the last few decades (in some places by as much as 90%), although recent increases in numbers have been encouraging. As a result, eastern bluebirds have been given some level of protection throughout their range. Two major hypotheses have been proposed to explain the decline, they are habitat destruction and competition. Much of the eastern bluebird's habitat has been turned into farmland or commercial property, greatly reducing food and shelter resources. Eastern bluebirds also compete with the more aggressive, introduced species, house sparrows and European starlings, for food and nesting sites. The most effective measure implemented to protect eastern bluebirds has been the introduction of nest boxes placed in good nesting habitat for bluebirds. These boxes are relatively easy to make and maintain and have been quite successful in places where they have been established.

Eastern bluebirds are listed as a species of "least concern" by the IUCN. They are not protected under CITES or the U.S. Endangered Species Act. There are an estimated 10,000,000 eastern bluebirds in North and Central America. (North American Bluebird Society, 1999; Terres, 1980; Tveten, 1993)

This species is the state bird of both Missouri and New York. Several other common names have been used to denote this bird, including American bluebird, Wilson's bluebird, Common bluebird, and others. In addition to S. sialis, there are two other species of bluebirds: Sialia mexicana (Western bluebird) and Sialia currucoides (Mountain bluebird). Both of these birds species have coloration and habits similar to that of S. sialis. Their ranges differ, although some range overlap occurs in the mid-west and central parts of the United States. Several cases of albinism have been seen within S. sialis, and hybrid crosses between Sialia species have been conducted, some of which were successful. (North American Bluebird Society, 1999; Robbins, et al., 1983; Terres, 1980)