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Field guide

Bluebirds are making a comeback — thanks to a little help from their friends

A female bluebird nests in a box.Donald Morse

While having dinner with my friends Kaori and Larry Kelts in Andover this summer, I saw a beautiful bird with a bright blue head, wings, and tail, rusty-colored chest, and white belly land on their lawn. I recognized it immediately as an eastern bluebird. I was thrilled. I don’t recall ever having seen a bluebird.

Kaori said two bluebird nest boxes were set up in their yard years ago by a friend, Don Morse.

“For a long time the nest in the yard was occasionally used by chickadees,” Kaori explained. “All of sudden, without any particular changes, bluebirds appeared a couple of years ago and started to use the front nest. This is the second year they nested and raised their young successfully.”

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In the 20th century, pesticides and competition with house sparrows negatively impacted bluebird populations, explained Wayne Petersen, Mass Audubon’s director of Important Bird Areas.

“House sparrows are very aggressive,” said Petersen. “They will attack bluebirds, bluebird eggs, and baby bluebirds. House wrens compete with bluebirds as well. And bluebirds don’t tend to fight back.”

But bluebirds have recovered in recent years, Petersen said, and are increasing in numbers, thanks in large part to people putting up nesting boxes in their yards and fields.

“Bluebirds have been very responsive to nesting in bird boxes,” said Petersen. “Some people and organizations, like the North American Bluebird Society, set up boxes and monitored them to make sure house sparrows didn’t occupy the boxes. They even set up bluebird trails — large numbers of bluebird boxes along roadsides and other areas. With a lot of TLC, bluebirds made a really remarkable comeback.”

Marcia Walsh, Merrimack College School of Health Sciences professor emeritus, said she and her husband, Don Morse ― yes, the same Don Morse ― put up a bluebird trail with about six boxes spaced apart in a field at their farm in Westford when they lived there several years ago. Walsh said the boxes were a special size, and Morse researched what the best structure was for the bluebirds.

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“We placed the boxes on steel posts,” said Walsh. “Blues do best when the boxes are facing east and positioned near a small tree so the fledglings have a place to fly to. We put dry pine needles on the ground below for nesting materials and offered mealworms we put in a tuna can on the stake to the residents! Some of the boxes were occupied by tree swallows, which got along just fine with the blues.”

Walsh said in winter, they had a station with a water heater and special bluebird cakes made of suet, oatmeal or cornmeal, peanut butter, sugar, and currants. The bluebirds remained all winter.

“What is most appealing about bluebirds is their gorgeous color and their sweet song,” said Walsh. “Also, seeing the blues in winter in the snow is a beautiful sight.”

Bluebirds natural nesting sites are holes in trees, said Petersen. They begin breeding in early spring, and usually lay four to five eggs. The eggs hatch in about two weeks, and the young typically leave the nest in 17 to 21 days. Bluebirds may produce two or three broods a summer.

Eastern bluebirds occur in southern Canada and in the US from New England to Florida, and the upper Midwest south to Texas, into Mexico and Central America, according to the Cornell Lab of Ornithology.

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Bluebirds are most common in Central Massachusetts and the Connecticut River Valley, but can be found throughout the state, said Petersen.

“The key is agricultural landscapes,” explained Petersen. “They like fields with scattered trees, with fences and wires for perching. Apple orchards are classic bluebird habitat. Golf courses and roadsides are also good bluebird habitat. They are more common in rural areas, but occur in suburbs, too. They’re not a city bird.”

Eastern bluebirds scour the grass under a frontyard bird feeder in Pembroke for fallen seed. They mostly forage for insects on the ground. John Tlumacki/Globe Staff

Eastern bluebirds feed mainly on insects on the ground, said Petersen. They’ll also eat soft fruit in winter.

Potential bluebird predators include Cooper’s and sharp-shinned hawks, said Petersen. Snakes that can climb — like rat snakes — and raccoons are potential nest predators.

Cavity nesting birds like bluebirds are also more inclined to get feather mites, lice, and ticks, Petersen added.

Bluebirds are small members of the thrush family, about two-thirds the size of robins, according to the Cornell Lab, and can live about 10 years.

Many bluebirds migrate to the Southeast in autumn, Petersen said, but increasing numbers have been overwintering in Massachusetts.

“Winters are milder because of climate change,” said Petersen. “And people feed them in the winter by putting out mealworms. If they can find food, they can manage.”

Petersen said several bluebirds may huddle together in holes in trees or bird boxes for warmth on cold winter nights.

“They’re very gentle birds and they’re beautiful ― you have to love them,” said Petersen. “Who doesn’t want a bluebird in their bird box? If a bluebird shows up, that’s as good as it gets.”

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Send your questions about nature and wildlife in the suburbs to donlymannature@gmail.com.