Harpswell Naturalist: Eastern bluebird

One of the pleasures of walking the golf course is enjoying the resident birds. Blue jay and tufted titmouse calls are always on offer, but you never know what will catch your eye. Yesterday it was a female eastern bluebird plucking a tuft of grass and flying toward her nest site. Spring breeding season is past, but these gorgeous birds attempt second, even third broods in favorable summer weather.

The eastern bluebird, Sialia sialis, is a member of the thrush family known for its lovely blue plumage and melodic calls. Of three bluebird species in North America, the eastern bluebird lives mostly east of the Rockies, from southern Canada through the eastern United States, extending south into Mexico and Central America as far as Nicaragua. While bluebirds are capable of migration flights up to 2,000 miles, the birds may remain in Maine thanks to recent milder winters.

You will generally find this bird in open woodlands, pastures or spots like Mitchell Field. They prefer sparse ground cover to spot food. Highly social outside the breeding season, they can gather in winter flocks of up to 100, but they become territorial while seeking a mate.

The adult male is a brilliant royal blue on his back and head, with a rich, reddish-brown breast and white underbelly. The adult female is more subdued, displaying subtle blue in her wings and tail, a grayish-brown back, a whitish eye ring and pale throat feathers. Fledglings are grayish-brown, with heavily speckled breasts that help them blend into their surroundings until their blue flight feathers emerge.

In spring, the male’s courtship display involves fluttering his wings and singing to his intended mate. He carries a symbolic bit of grass into a nest box or a tree cavity to entice the female. Once she enters, a bond is established that may last through several breeding seasons. While the male sits outside fluttering his wings, the female builds the nest. She weaves dry grasses and pine needles into a neat, cup-shaped nest, lining it with fine grass, animal hair, or feathers.

While the pair may investigate multiple cavities, the female will lay eggs in only one. The female incubates three to seven pale blue eggs until they hatch in roughly two weeks. Both parents bring food to the nest, and juveniles from an earlier brood may help feed their younger siblings. The young are ready for flight within three weeks.

Bluebirds sit on high perches, such as fence posts or wires, scanning for insects, spiders, grasshoppers, snails or worms. In autumn and winter, they switch to eating berries, wild grapes, sumac and winterberries. At times, they eat larger prey like salamanders, tree frogs or shrews. Bluebirds have excellent eyesight and can spot prey from 50 feet away, often grabbing insects right out of the air. If you want to attract bluebirds to your feeders, offering live or dried mealworms is a proven method for success.

The birds have a range of calls, including a soft, warbled whistle that sounds like “tur-a-lee,” a soft “chew-wee,” and quick alarm calls. Their average lifespan is roughly five years in the wild, but one bird recovered in South Carolina had been banded in New York more than 10 years earlier.

Wooden nesting boxes have become the standard method for attracting nesting bluebirds across the country. They are readily available, but you can also build your own. Late autumn or winter is an ideal time to install a box, before returning males look for nest sites. Use a box with a 1.5-inch entry hole to exclude larger competitors. Install the box on a pole in an open location, at least 50 feet from dense tree lines. A predator guard below the box will keep out snakes, squirrels, mice and raccoons.

Competition for nest sites can be keen, so you may see bluebirds jockeying with tree swallows, sparrows and chickadees. If you install two boxes within 5 feet of each other, bluebirds are happy to have other species as neighbors. Each year, scrape out the old nests and clean the box with mild soap and warm water.

Bluebirds suffered population declines into the 1960s thanks to pesticide use and habitat loss. Populations now are stable or rising in most areas, thanks to their many fans who installed nesting boxes and to forest management practices that leave dead trees standing. With continued vigilance, we can enjoy these beautiful birds for the long haul.