Thursday, July 18, 2024

A bluebird in April at the beginning of breeding season. (Photo: Richard George)

When the first English colonists arrived in Massachusetts, they found Eastern bluebirds (Sialia sialis) in the fields and forest edges. These brilliant blue birds with red chests reminded the settlers of European robins, so they called the birds blue-robins. Years later, Henry David Thoreau would describe the bluebird as carrying the sky on its back.

In the 1850s, New York City imported house sparrows to combat linden moths, which were devouring city trees. Hundreds of house sparrows were released to combat inchworm infestations by officials in Boston; New Haven, Connecticut; Philadelphia; and Rhode Island. In the 1870s, the Cincinnati Acclimatization Society let loose thousands of songbirds including house sparrows to “aid people against the encroachment of insects.” 

A bluebird on the Cambridge-Watertown line. (Photo: Mark Rosenstein)

House sparrows are aggressive. These birds attacked bluebirds, bluebird eggs and baby bluebirds. Throughout the 1900s, house sparrows and introduced European starlings challenged bluebirds for nesting cavities and food. And if that wasn’t enough, pesticides such as DDT killed the insects that bluebirds needed to survive. By the 1970s, the bluebird population in the Northeast had declined by 90 percent. Today, thanks largely to people who have installed bluebird houses, numbers in our commonwealth are stable or increasing.

A female bluebird has a grayish head and back. (Photo: Richard George)

The first bluebirds return to our area in March and April, where they nest in cavities. They are happy in either a human-made nest box or a natural woodpecker hole. The female lays about five eggs, which hatch in two weeks. The young leave the nest in about two more weeks. Together the bluebird couple raises two broods during the summer, feeding them insects such as caterpillars, spiders or worms. 

Bluebird populations are stable or increasing thanks to an abundance of nest boxes. (Photo: Richard George)

Later in the season, while the female sits on her second set of eggs, the male attends to the needs of the first brood. These fledglings have left the nest, but they are not completely independent. By the time the second set of eggs hatch, the first brood are self-sufficient, and they may help feed the new chicks. Two-thirds of a bluebird diet is insects. The young bluebirds stay in the vicinity of the nest throughout the summer and fall until it is time to migrate south for the winter.

A bluebird surveys the scene in Lincoln in February 2022. (Photo: Richard George)

In October, flocks of bluebirds fly south, but some will overwinter if food is available. These overwintering birds eat mostly soft fruits, for they are not seed-eaters. A bluebird pair might elect to stay on or near their breeding territory all winter. Massachusetts lies at the northern edge of bluebirds’ winter range, so overwintering is becoming more and more common.

The birds that do not overwinter return at the first sign of warm weather. Sometimes the weather turns cold again – to the birds’ detriment. Ornithologist Aaron Clark Bagg and co-author Samuel Atkins Eliot Jr. in 1937 cite a Springfield, Massachusetts, newspaper story about a pair of bluebirds: 

On March 28 a pair of Bluebirds came to the feeding station of Charles J. Anderson . . . and after eating began to flutter and peck at the window. It was cold outside, so after talking to them through the glass, Mrs. Anderson let them in. The male was hardy, but the female manifestly required warmth. She was given warm milk to drink, and warbled her thanks. For three days, while the cold spell lasted, she returned periodically to get warm inside the room.

A bluebird finds a caterpillar. (Photo: Richard George)

Bluebirds are not city birds, but can be found nearby in open fields, parks, cemeteries, golf courses, swamps or other open spaces with scattered trees. They like fences, wires or branches for perching. Eastern bluebirds are members of the thrush family, a group of birds noted for singing and chatter. Bluebirds are no exception. People have long enjoyed the warbling of the bluebird. As Henry David Thoreau wrote in his poem “The Bluebirds:”

The bluebird had come from the distant South
To his box in the poplar tree,
And he opened wide his slender mouth,
On purpose to sing to me.

A bluebird in February 2022. Some bluebirds overwinter in our region. (Photo: Richard George)

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Jeanine Farley is an educational writer who has lived in the Boston area for more than 30 years. She enjoys taking photos of our urban wild things.