Montana Field Guide

Eastern Bluebird - Sialia sialis

The Eastern Bluebird is a small thrush (16 to 21 cm long) with a wingspan of approximately 33 cm. The male has a bright blue back, head, wings, and tail. The throat, sides of the neck, and upper breast are orange, with the orange on the breast extending down the flanks. The white belly is bright and apparent. The female is similarly colored, but is duller overall. The head and back are more of a gray or gray-blue than blue, but the wings and tail are primarily blue. Unlike the male, the female has a white throat. On both sexes, the eye is black, and the bill is dark and stout, with a yellow gape (Gowaty and Plissner 1998, Sibley 2000).

Vocalization of the Eastern Bluebird is described as a song of mellow whistles sounding somewhat like "chiti WEEW wewidoo" or "Tu-a-wee" (Gowaty and Plissner 1998, Sibley 2000). The male sings loudly from high, conspicuous perches, sometimes during flight (Gowaty and Plissner 1998).

The plumage of the male Eastern Bluebird is most similar to that of the Western Bluebird. The Eastern is discernable by its white belly, orange throat and blue scapulars, while the Western has a blue belly and throat and chestnut scapulars. The features distinguishing the female Eastern, Western, and Mountain bluebirds are less distinct. The Eastern Bluebird female is distinguishable from the Western by the white throat, rufous on the sides of the neck, and more distinct rufous flanks. The Eastern is darker overall than the Mountain Bluebird, with more rufous-orange on the flanks, upper breast, and sides of the neck. The Western and Mountain Bluebird females lack the white throat. In addition, the bill of the Eastern Bluebird is thicker and stouter than that of the two other bluebird species.

Montana Range

Based upon limited records, spring arrival occurs in May. Records indicate that birds are present through August, and fall migration begins soon after. In 1990, the presence of an individual bird was recorded at Long Pines, Carter County as late as October (Montana Bird Distribution 2003).

Limited specific information exists on habitat use by Eastern Bluebirds in Montana, but the species may generally be limited to the deciduous trees (primarily cottonwood, Populus spp.), along the rivers of eastern Montana, which can provide significant habitat where nest boxes haven't supplanted these natural nesting sites (Johnsgard 1986, Gowaty and Plissner 1998).

Other frequently used habitats can include pastures, roadsides, farmlands, meadows, yards, and other open grassy areas that might provide adequate foraging habitat (Northern Prairie Research Center 2003). Reports of breeding in the state indicate the use of nesting boxes, with other potential nesting sites including old woodpecker holes and natural cavities in riparian forests, shelterbelts, farmsteads and city parks (Johnsgard 1986, Montana Bird Distribution 2003).

No information regarding food habits exist for Eastern Bluebird in the state. Other studies outside of Montana indicate Eastern Bluebirds eat mainly insects, but will also consume other invertebrates and small fruits. Primarily a ground-forager, this bird will perch on a branch, post, or wire and swoop to catch prey items on or near the ground (Northern Prairie Research Center 2003). Orthoptera and beetles comprise a large portion of the Eastern Bluebird's diet (Terres 1980). While foraging fruit, which this species consumes primarily in late summer and into winter, the bird will land on the stalks of fruiting bushes or in trees to pluck fruit from the perch (Gowaty and Plissner 1998). Eastern Bluebirds may also be observed gleaning insects from foliage.

No Eastern Bluebird ecological information is available from Montana. Studies from other areas in the species' range state that Eastern Bluebirds are a territorial species and are known to prefer nesting boxes that are at least 100 yards from other bluebird nests (Gowaty and Plissner 1998). Nesting territories range from 1.1 to 2.0 hectares in size, and decrease as the nesting season advances, possibly in response to an increase in food availability or the need for parents to more closely protect the nestlings (Gowaty and Plissner 1998).

Ectoparasites of the Eastern Bluebird include lice (Philopterus sialii, Ricinus sp.); mites (Analgopsis sp. and Dermanyssus prognephilus) (Peters 1936 as cited in Gowaty and Plissner 1998); flies (Ornithomyia anchineuria); eye worms (Oxyspirura pusillae) (Pence 1972 as cited in Gowaty and Plissner 1998); nasal mites (Sternostoma siliphilus and Boydaia spatulata) (Pence 1973 as cited in Gowaty and Plissner 1998); and trematodes (Collyriclum faba) (Kibler 1968, Pinkowski 1976 as cited in Gowaty and Plissner 1998). Predation by chipmunks (Tamias sp.), and flying squirrels (Glaucomys volans) on the Eastern Bluebird is common, the former species raids the nests and eats eggs or young. Adults, nestlings, and/or young can become prey to the House Sparrow, European Starling, domestic cat (Felis domesticus), black bear (Ursus americanus), raccoon (Procyon lotor), and American Kestrel (Falco sparverius) (Gowaty and Plissner 1998).

Given the rarity of records in the state (less than 25), relatively numerous nesting observations exist for Montana. The thirteen breeding records indicate that at least three eggs have been produced (when eggs have been observed) and on more than one occasion four fledglings have been noted. Four breeding accounts indicate that nesting took place in nest boxes, with breeding dates ranging from May to July (Montana Bird Distribution 2003).

Other than the placement of nesting boxes in appropriate habitat, no management activities designed specifically for the Eastern Bluebird in Montana are known.