Eastern Bluebird Life History

Habitat

Habitat GrasslandsEastern Bluebirds live in open country around trees, but with little understory and sparse ground cover. Original habitats probably included open, frequently burned pine savannas, beaver ponds, mature but open woods, and forest openings. Today, they’re most common along pastures, agricultural fields, suburban parks, backyards, and golf courses.Back to top

Food

Food InsectsInsects caught on the ground are a bluebird’s main food for much of the year. Major prey include caterpillars, beetles crickets, grasshoppers, and spiders. In fall and winter, bluebirds eat large amounts of fruit including mistletoe, sumac, blueberries, black cherry, tupelo, currants, wild holly, dogwood berries, hackberries, honeysuckle, bay, pokeweed, and juniper berries. Rarely, Eastern Bluebirds have been recorded eating salamanders, shrews, snakes, lizards, and tree frogs.Back to top

Nesting

Nest Placement

Nest CavityEastern Bluebirds put their nests in natural cavities or in nest boxes or other artificial refuges. Among available natural cavities, bluebirds typically select old woodpecker holes in dead pine or oak trees, up to 50 feet off the ground. Older bluebirds are more likely than younger ones to nest in a nest box, although individual birds often switch their preferences between nesting attempts. When given the choice in one study, bluebirds seemed to prefer snugger nest boxes (4 inches square instead of 6 inches square on the bottom) with slightly larger entrance holes (1.75 inch rather than 1.4 inch diameter).

Nest Description

After a male Eastern Bluebird has attracted a female to his nest site (by carrying material in and out of the hole, perching, and fluttering his wings), the female does all the nest building. She makes the nest by loosely weaving together grasses and pine needles, then lining it with fine grasses and occasionally horse hair or turkey feathers. Nest boxes in some places are so common that a single territory may contain several suitable holes. Females often build nests in each available hole, but typically only use one of these. Bluebirds may use the same nest for multiple broods.

Nesting Facts
Clutch Size:2-7 eggs
Number of Broods:1-3 broods
Egg Length:0.7-0.9 in (1.8-2.4 cm)
Egg Width:0.6-0.8 in (1.5-1.9 cm)
Incubation Period:11-19 days
Nestling Period:17-21 days
Egg Description:Pale blue or, rarely, white.
Condition at Hatching:Naked except for sparse tufts of dingy gray down, eyes closed, clumsy.
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Behavior

Behavior Ground ForagerThis small, brightly colored thrush typically perches on wires and fence posts overlooking open fields. The birds forage by fluttering to the ground to grab an insect, or occasionally by catching an insect in midair. Bluebirds can sight their tiny prey items from 60 feet or more away. They fly fairly low to the ground, and with a fast but irregular pattern to their wingbeats. Males vying over territories chase each other at high speed, sometimes grappling with their feet, pulling at feathers with their beaks, and hitting with their wings. The boxes and tree cavities where bluebirds nest are a hot commodity among birds that require holes for nesting, and male bluebirds will attack other species they deem a threat, including House Sparrows, European Starlings, Tree Swallows, Great Crested Flycatchers, Carolina Chickadees, and Brown-headed Nuthatches, as well as non-cavity nesters such as robins, Blue Jays, mockingbirds, and cowbirds. Males attract females to the nest with a display in which he carries bits of nesting material into and out of the nest. Once a female enters the nest hole with him, the pair bond is typically established and often remains intact for several seasons (although studies suggest that around one in every four or five eggs involves a parent from outside the pair).Back to top

Conservation

Conservation Low ConcernEastern Bluebird populations increased between 1966 and 2015, according to the North American Breeding Bird Survey. Partners in Flight estimates a global breeding population of 22 million, with 86% spending at least some part of the year in the U.S., 22% in Mexico, and 1% breeding in Canada. The species rates a 7 out of 20 on the Continental Concern Score, and is not on the 2016 State of North America's Birds' Watch List. Eastern Bluebird populations fell in the early twentieth century as aggressive introduced species such as European Starlings and House Sparrows made available nest holes increasingly difficult for bluebirds to hold on to. In the 1960s and 1970s establishment of bluebird trails and other nest box campaigns alleviated much of this competition, especially after people began using nest boxes designed to keep out the larger European Starling. Eastern Bluebird numbers have been recovering since.Back to top

Backyard Tips

This species may visit backyards if food is offered. It doesn't often come to feeders, unless you have feeders that provide mealworms. Find out more about what this bird likes to eat and what feeder is best by using the Project FeederWatch Common Feeder Birds bird list.

Eastern Bluebirds are a great prospect for nest boxes if you have the space to put one up in your yard, and if your yard isn’t too hemmed in by trees or houses. Consider putting up a nest box to attract a breeding pair. Make sure you put it up well before breeding season. Attach a guard to keep predators from raiding eggs and young. Find out more about nest boxes on All About Birdhouses, where you'll find plans for building a nest box of the appropriate size for Eastern Bluebird.

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Credits

Dunne, P. (2006). Pete Dunne's essential field guide companion. Houghton Mifflin Harcourt, New York, USA.

Ehrlich, P. R., D. S. Dobkin and D. Wheye (1988). The birder's handbook. A Field Guide to the natural history of North American birds, including all species that regularly breed north of Mexico. Simon and Schuster Inc., New York, USA.

Gowaty, Patricia A. and Jonathan H. Plissner. 2015. Eastern Bluebird (Sialia sialis), version 2.0. In The Birds of North America (P. G. Rodewald, editor). Cornell Lab of Ornithology, Ithaca, New York, USA.

Lutmerding, J. A. and A. S. Love. Longevity records of North American birds. Version 2015.2. Patuxent Wildlife Research Center, Bird Banding Laboratory 2015.

Partners in Flight (2017). Avian Conservation Assessment Database. 2017.

Sauer, J. R., D. K. Niven, J. E. Hines, D. J. Ziolkowski, Jr., K. L. Pardieck, J. E. Fallon, and W. A. Link (2017). The North American Breeding Bird Survey, Results and Analysis 1966–2015. Version 2.07.2017. USGS Patuxent Wildlife Research Center, Laurel, MD, USA.

Sibley, D. A. (2014). The Sibley guide to birds, second edition. Alfred A. Knopf, New York, USA.

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