Provided courtesy of National Audubon Society, Inc.
By:  Stephen W. Kress, Vice President of Bird Conservation

Bluebirds nested primarily in woodpecker holes and other natural cavities during colonial days. They were once abundant in rural and agricultural habitats, but they are vulnerable to changes that people are bringing to their world. Bluebird populations decline where farmland converts to forest; where suburbs replace open space and where they encounter their archrivals-- alien House Sparrows and European Starlings that aggressively compete for scarce nesting cavities.

Fortunately, caring people are helping the three North American species and Western, Mountain and Eastern Bluebirds are staging an impressive comeback. The nest box is the primary tool making a difference for these beautiful birds. Some enthusiasts are even creating bluebird trails containing hundreds of boxes. You can help bluebirds and other native, cavity-nesting birds such as chickadees, titmice, wrens and swallows by carefully locating and maintaining your new nest box. Here are some tips:

Selecting a site

• Bluebirds prefer farmland, meadows, rural schoolyards, cemeteries and other open habitats. They rarely nest in woodlands and cities.

• Locate your nest box within 50 feet of a tree, tall shrub or other solitary perch. The adults use this to scan the ground for insect prey and the young use the perch on their first flights from the box. This keeps them off the ground and reduces risk from predators.

• Mount the box on a freestanding ¾" galvanized pipe, Audubon pole, or sturdy fencepost about 5 feet off the ground. Face the box away from prevailing winds and preferably toward the nearest tree or shrub so that young birds can easily fly to the perch rather than landing on the ground.

• Avoid locating your nest box near a forest edge or shrubby hedgerow. This reduces risk of competition with House Wrens, which often displace bluebirds with their bulky stick nests. Also avoid placing the nest box in locations such as barnyards and cities where House Sparrows are common. Like House Wrens, House Sparrows can usurp nest boxes from bluebirds.

• The diameter of the entrance hole for your nest box will likely exclude European Starlings, but House Sparrows and House Wrens may attempt to use the box. To favor bluebirds, remove House Sparrow nests and consider relocating the box to a site where these sparrows are less of a concern. Habitat considerations are the best way to determine which species will use your box. Bluebirds rarely nest in wooded habitats, but chickadees, titmice and Great-crested Flycatchers may use the box if it is placed in the woods. This bluebird box features a predator protector, which is the block of wood surrounding the entrance hole. This will assist in protecting the young birds from predators reaching in the nesting box.

• Tree Swallows and Violet Green Swallows also compete with bluebirds for nest boxes. The best way to benefit both bluebirds and swallows is to place two boxes near each other. By placing boxes 5-15’ apart, the highly territorial swallows will chase other swallows from the vicinity of their nest, but they will usually not fight with a neighboring bluebird.

• Avoid using garden and lawn pesticides. Bluebirds and other cavity-nesting birds are primarily insect-eaters and are very vulnerable to poisoning from pesticides. Lawn chemicals not only kill backyard birds, but runoff from yards into nearby wetlands and ground water can affect wildlife far from your home.

• Plant berry-producing shrubs that provide food throughout the seasons- bluebirds especially like flowering dogwood, serviceberries, elderberries, spicebush, hollies and blueberries.

Maintaining your nest box

• At the end of each nesting season (usually by October) clean out your nest box by removing old nesting material. If nest boxes are not cleaned, bluebirds will usually build a new nest on top of the old nest, which makes their eggs and young vulnerable to predators such as raccoons. Cleaning will also reduce the risk of over wintering blowflies and other parasites.

• Clean out accumulated nesting material, old wasp nests and other debris with a spatula or ice scraper. Use a dilute mixture of bleach (1 part bleach to 10 parts water) if you encounter parasites in the nest box. By cleaning out nests in the fall, you are making the box available for winter- roosting by bluebirds or other cavity nesters that spend cold winter nights in boxes.

• Clean out your nest boxes a second time in late February (in southern states) or early March- just prior to the beginning of the bluebird nesting cycle. This cleaning will remove mouse nests that can fill up the boxes and preclude nesting.

• You can follow the progress of the nesting cycle by carefully opening the box once a week. If you discover wasps nesting in the roof of the box, scrape off the nests with a spatula in the early morning before the wasps become active. If wasps are a chronic problem, coat the roof of the box with candle wax.

Bluebird biology

• Bluebirds begin nesting in late February in the southern U.S. and late March to early April in the north. Bluebirds stay on their nesting territories throughout the year in the south, but usually leave the north in the winter.

• Bluebirds lay 4-5 light blue eggs (sometimes white) and incubate for 12-14 days.

• Both parents feed the young for 18-21 days. Two to three broods are common.

• Ten or more bluebirds may use a nest box as a communal roost in the winter.

Common nests

Bluebirds build a tall, cup-shaped nest from fine grass, sometimes entwined with pine needles. Bluebirds usually lay 4-6 light blue eggs, but occasionally the eggs are white. Habitat: Meadows, fields with scattered trees or shrubs. Tree Swallows and Violet-Green Swallows construct a nest similar to bluebirds, but usually line it with feathers. They lay 4-7 white eggs that are smaller than bluebird eggs.

Habitat: Meadows, fields and wetlands with scattered trees and shrubs. House Wrens usually fill the nest box with twigs and line their bulky nest with feathers and course grass. They lay 5-6 buff-colored eggs with dark brown speckles.

Habitat: Forest edge, brushy fencerows, gardens. House Sparrows use course grass to build a bulky nest with a dome-shaped roof, often they add feathers, plastic, etc. Their eggs are white with dark brown speckles.

Habitat: Near houses, barns, city parks. Chickadees build a small, cup-shaped nest from moss and plant down and line the nest with fine hair or animal fur. They lay 5-8 tiny white eggs with reddish speckles.

Habitat: Forest edge and interior. Titmice construct a cup-shaped nest from moss and grass, lined with fur, feathers and scraps of snakeskin. Titmice lay 5-7 small eggs. The eggs are cream-colored with brown speckles.

Habitat: Forest edge and interior.

For More information on nest boxes and plantings to create backyard bird habitat, consult: The Audubon Society Bird Garden by Stephen W. Kress. 1995. Dorling Kindersley, New York. Also visit the Audubon at Home website: www.audubonathome.org

For information about Audubon, including how to become a member, visit our website at www.audubon.org or call 800-274-4201.

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