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Sialia sialiseastern bluebird

By Kate Fimbel

Geographic Range

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)

Habitat

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)

Physical Description

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)

  • Sexual Dimorphism
  • female larger
  • sexes colored or patterned differently
  • male more colorful
  • Range mass
    27 to 34 g
    0.95 to 1.20 oz
  • Range length
    16 to 21 cm
    6.30 to 8.27 in
  • Average length
    18 cm
    7.09 in

Reproduction

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)

  • Breeding interval
    A mature female typically raises two broods each season.
  • Breeding season
    Eastern bluebirds breed in the spring and summer.
  • Range eggs per season
    3 to 7
  • Average eggs per season
    4
    AnAge
  • Range time to hatching
    13 to 16 days
  • Range fledging age
    15 to 20 days
  • Average age at sexual or reproductive maturity (female)
    1 years
  • Average age at sexual or reproductive maturity (male)
    1 years

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)

  • Parental Investment
  • altricial
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • male
      • female
    • protecting
      • female
  • pre-independence
    • provisioning
      • male
      • female

Lifespan/Longevity

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.

Behavior

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.

  • Range territory size
    0.011 to 0.084 km^2

Home Range

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

Communication and Perception

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)

Food Habits

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)

  • Animal Foods
  • insects
  • Plant Foods
  • seeds, grains, and nuts
  • fruit

Predation

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)

Ecosystem Roles

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.

Economic Importance for Humans: Positive

Eastern bluebirds may help to control insect populations.

  • Positive Impacts
  • controls pest population

Economic Importance for Humans: Negative

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

Conservation Status

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)

Other Comments

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)

Contributors

Tanya Dewey (editor), Animal Diversity Web.

Kari Kirschbaum (editor), Animal Diversity Web.

Kate Fimbel (author), Southwestern University, Stephanie Fabritius (editor), Southwestern University.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

acoustic

uses sound to communicate

agricultural

living in landscapes dominated by human agriculture.

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

cooperative breeder

helpers provide assistance in raising young that are not their own

diurnal
  1. active during the day, 2. lasting for one day.
endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

insectivore

An animal that eats mainly insects or spiders.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

migratory

makes seasonal movements between breeding and wintering grounds

monogamous

Having one mate at a time.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

polymorphic

"many forms." A species is polymorphic if its individuals can be divided into two or more easily recognized groups, based on structure, color, or other similar characteristics. The term only applies when the distinct groups can be found in the same area; graded or clinal variation throughout the range of a species (e.g. a north-to-south decrease in size) is not polymorphism. Polymorphic characteristics may be inherited because the differences have a genetic basis, or they may be the result of environmental influences. We do not consider sexual differences (i.e. sexual dimorphism), seasonal changes (e.g. change in fur color), or age-related changes to be polymorphic. Polymorphism in a local population can be an adaptation to prevent density-dependent predation, where predators preferentially prey on the most common morph.

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

suburban

living in residential areas on the outskirts of large cities or towns.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

visual

uses sight to communicate

References

Gowaty, P., J. Plissner. 1998. Eastern Bluebird (Sialis sialis). Pp. 1-32 in A Poole, F Gill, eds. The Birds of North America, Vol. 381. Philadelphia, PA: The Birds of North America, Inc.

North American Bluebird Society, 1999. "Fact Sheet: Getting Started with Bluebirds" (On-line). Accessed December 1, 1999 at http://www.nabluebirdsociety.org/start.htm.

Robbins, C., B. Bruun, H. Zim.. 1983. A Field Guide to the Birds fo North America. New York: Golden Books.

Terres, J. 1980. The Audubon Society: Encyclopedia of North American Birds. New York: Alfred A. Knopf.

Tveten, J. 1993. Birds of Texas. Fredricksburg, TX: Shearer Publications.

USGS Northern Prairie Wildlife Research Center, 1999. "Eastern Bluebird (Sialia sialis)" (On-line). Accessed December 4, 1999 at http://www.npwrc.usgs.gov/resource/birds/eastblue/eastblue.htm.

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