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Nature Notes: Eastern Bluebird

Ed Robinson
February 1, 2017
Curt Chipman photo

This winter has been fairly mild, and that may mean you’ll see some of your favorite birds a bit earlier this spring. One of my favorites is the Eastern bluebird (Sialia sialis), a member of the thrush family, known for their soft plumaged, plump figures and melodic calls. If you are lucky enough to have bluebirds nesting around your home, you can look forward to a beautiful bit of color in your days until they move on after summer.

Of four bluebird species found in North American, the Eastern is found mostly east of the Rockies, from southern Canada to Florida, Texas, Baja and as far south as Nicaragua. While some birds may fly up to 2,000 miles during a seasonal migration, others choose to remain in their spring and summer habitats hoping to survive the winter. You will generally find this bird in open woodlands and pastures, fields, backyards and golf courses, and they prefer little understory and sparse ground cover so they can spot food items. This is a very social bird, and they can gather in flocks up to 100, but will become territorial during mating season

Thrushes in general are fairly small, with the bluebird running to about seven inches long, with a wingspan of around 13 inches. The adult male is a brilliant royal blue on his back and head, with a rich, red-brown breast. The adult female has tinges of blue in her wings and tail that are more subtle, a whitish eye ring and brown lateral stripes on her throat. Fledglings and juveniles are grayish, with speckled breasts.

When springtime thoughts turn to love, the male will flutter and display his wings while singing during courtship. He will also carry bits of grass into the chosen nest cavity or nest box, hoping to attract a female. Once the female enters the cavity, a bond is established that may last through several breeding seasons. The male brings nesting material to the site, and sits outside, flapping his wings as if he deserves all the credit for nesting success. The female weaves the grasses and pine needles into a cup shaped nest, then lines it with finer grasses, animal hair or feathers.

If multiple suitable sites are available within their territory, the pair may build multiple nests but lay eggs only in one. She will sit on the nest, incubating three to seven pale blue or white eggs. The incubation period is 12 to 17 days. Both parents bring food to the nest, and juveniles from an earlier brood may help out. The young are ready to leave the nest within three weeks. Depending on survival, the pair may have two or even three broods in one nesting season.

Bluebirds enjoy sitting on a perch such as a fence post or wire and scanning for insects, spiders, grasshoppers, snails, worms and, in the autumn and winter, berries, wild grapes, even apples. They have also been observed catching and eating larger prey such as salamanders, small snakes, lizards, frogs and shrews. Bluebirds have excellent eyesight and can spot prey from 50 to 60 feet away, and are capable of grabbing insects in the air. They are also known to flutter next to a fruit bearing bush to feed.

The birds have a range of calls, including a short, soft set of quick, warbled whistles that may sound like “tur a lee,” or a soft “chew wee” and short calls that sound like “chit.” Their average life span is probably four to six years in the wild, but one deceased bird recovered in South Carolina had been banded in New York more than 10 years earlier.

John Berry photo

Wooden nesting boxes have been extremely successful in attracting bluebirds, and millions of them have been installed in the last few decades (although many of them are not properly maintained to keep them clean and ready for the next occupants). You will find a number of these at HHLT preserves, including Curtis Farm and Johnson Field, as well as the town-owned Mitchell Field. This is a good time of year to install the boxes, before the birds begin looking for nest sites. The dimensions of the boxes are important for nesting success, so either buy a box or a kit for assembly, or find a set of plans on the internet if you wish to build your own. It is important for the boxes to be installed in relatively open locations, not in or near a tree line. A guard is suggested below the box to keep out snakes, squirrels, and raccoons hoping to steal the eggs or fledglings. Competition for prime nesting sites can be keen, so you may see bluebirds jockeying with sparrows, swallows, chickadees and more.

If you want to attract bluebirds to your feeders, the recommended feed is meal worms, but friends have reported seeing them this winter on general bird seed mixes.

While bluebird populations declined into the 1960’s due to pesticide use and loss of habitat from indiscriminate tree cutting and housing expansion, today populations are stable or rising in most areas, thanks to bluebird supporters who installed nesting boxes, or informed wood cutters who now leave some dead trees standing. After clearing all of the living aspens in a one acre patch at my old farm in New York, last spring I observed bluebirds using cavities in three old snags left for that purpose. The species is not currently under threat so we can look forward to this beautiful visitor to our neighborhoods for a long time to come.

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