Species Profile
This familiar species nests across much of the East and winters south to Nicaragua. A bluebird is six inches long and weighs about an ounce. Males have a vivid blue back and wings and a ruddy breast while the females have a more muted blue-gray back and less vividly colored breast. When not nesting, bluebirds wander in small feeding flocks sometimes with house finches and other songbirds. They favor semi-open habitats: orchards, pastures, hayfields, fence lines, cut over or burned areas, forest clearings, open woodlots, and suburban gardens and parks. The song consists of three or more soft, melodious and mellow whistled notes (“tury cherwee,cheye-ley,” as one observer has rendered it). Bluebirds eat crickets, grasshoppers, beetles, caterpillars, and many other insects, and they take spiders, centipedes, earthworms, and snails. Often they sit on a low perch, then flutter down to catch prey from vegetation or the ground. In fall and winter they turn to fruits, including those of sumac, dogwood, Virginia creeper, poison ivy, pokeweed, elderberry, wild cherry, bittersweet, honeysuckle, and wild grape. On sunny or warm winter days, they can turn back to insects for food if they are available.
Bluebirds are permanent residents in the southern parts and lower elevations of their range. In winter, bluebirds from northern areas and higher elevations may shift southward and to the valleys. In mild winters you may see many bluebirds in the agricultural valleys of central Pennsylvania. If they ever left their nesting ground, bluebirds return to their breeding grounds in March and April, welcomed as harbingers of spring by winter weary rural folk. Bluebirds nest statewide in Pennsylvania, avoiding deep woods and wooded ridges. The population of Sialia sialis probably peaked around 1900, when farmland covered two thirds of the state. The number of bluebirds waned for many years thereafter as unprofitable acres were abandoned and grew back up in forest, but bluebird numbers have risen over the last several decades thanks to thousands of bluebird boxes put up by humans.
The courting male sings to the female and flutters close to her with his wings and tail spread; he may pass food to her. Mated pairs preen each other’s feathers. A study in New York found that bluebird territories used for mating, nesting, and feeding averaged over five acres. Bluebirds nest in abandoned woodpecker holes, tree cavities, hollow fence posts, and artificial boxes put up for them by humans. Bluebirds may face stiff competition for these sites from European starlings, house sparrows, tree swallows, and house wrens, all of which have been known to kill adult bluebirds. Bluebirds tend to like more open situations for nesting than competing house wrens, informing us as to the better locations for nest box placement. The female builds a loose nest inside the cavity out of grasses and weed stalks, sometimes lining a central cup with feathers or animal hair. Early nesters, bluebirds lay first clutches by late March or early April and second clutches by early June. Some pairs will nest three times in a season. The three to six eggs (usually four or five) are pale blue and unmarked. The female incubates them for about two weeks. Both parents feed the nestlings. After about eighteen days, fledglings leave the nest. Second and third clutches will usually have one fewer egg than a first clutch produced by the same pair.
Bluebird Nesting Box Plan
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How to Build a Bluebird Box
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