Eastern Bluebirds Natural History

The brilliant blue male Bluebird has a rusty throat, breast and sides, and white belly. He sits high atop a dead tree or branch, TV antenna, or power line to hunt for insects that make up two-thirds of his diet. He and his mate also eat wild berries, especially in cold weather when insects are not available. They rarely damage cultivated crops and are very beneficial to farmers and gardeners by eating insects. The young bluebirds have spotted breasts until fall molt.

As early as the end of February and as late as July, the male Bluebird locates a nesting site, establishes territory around it of two to five acres, and sings to attract a female and to warn other male Bluebirds to stay away. Once a female accepts the site, she builds a neat cup-shaped nest of dry grasses or pine needles. Nest building may take five days to three weeks.

The female lays one blue, or somewhat rare, a white (approximately 5%) egg each morning until three to six eggs are produced. The female begins incubating the eggs after the final egg is laid. Thirteen to fourteen days later, all viable eggs will normally hatch with hours of each other.

The adults begin feeding the young immediately after hatching, starting with soft insects and graduating to courser food as the nestlings grow. The adults also keep the nest clean by removing the fecal sacs that enclose the nestlings’ waste. The nestlings grow very rapidly, with their eyes opening on about the eighth day. By the time the nestlings fledge (leave) the nestbox, 16 to 20 days after hatching, they will be nearly the size of an adult Bluebird.

Usually, the entire brood of fledglings leaves the box within two hours. The fledglings can fly fifty to one hundred feet on their first flight and try to land in a bush, shrub, or low branch to avoid predators. The adults continue to care for the young and teach them to forage for food. The male Bluebird will continue this job while the female begins her second or third nest. On occasion, the young from a first nesting will help feed the nestlings from their parents’ second or third nesting.

After nesting season is over, Bluebirds give up their territories and flock together. South Carolina Bluebirds do not migrate. They are joined by migrant northern Bluebirds and roam the area looking for berries. In winter, bluebirds will roost in pine tree stands and nestboxes to avoid cold weather.