Although Eastern bluebirds have never been extinct in Michigan, bird lovers have been concerned about this popular member of the thrush family for more than 100 years. The winter of 1894-95 with its record cold and deep snow caused heavy mortality among certain semi-hardy species including the eastern bluebird and American robin. Although bluebirds were able to bounce back from this major loss, they then had to compete with introduced species from Europe such as the English or house sparrow and the European starling. With these introductions there was increased competition for cavity nesting sites, which further decreased bluebird populations.
By 1950, bluebirds were no longer common around people's homes. In addition to bad winters and foreign bird competition, habitat changes also contributed to their decline. As farming practices changed from small family farms to large operations, many fencerows were removed. Subsequently, this removed nesting cavities found there in trees and wooden posts, reducing bluebird nesting sites. Also, the increase in pesticide use and the gradual shift to more row crops had a negative impact on the bluebird's food availability. However, thanks to public education and a concerted effort by many people to provide nest boxes, bluebirds have made a comeback in recent years.
Bluebirds can be found throughout the state, and are most common in rural areas. They prefer grassland habitat with scattered trees; especially where trees are large enough to provide nesting cavities and provide shelter from early spring storms. Bluebirds are found in old fields, abandoned orchards, open woodlands, oak savannas, oak barrens, jack-pine barrens, and the edges of bogs and sedge meadows. They usually avoid heavily forested areas, even during migration. Common associates of bluebirds include eastern kingbirds, tree swallows, field sparrows and American gold-finches. Most or all of these species will benefit from management for bluebirds.
Although this popular songbird nests in every Michigan county, it is most common in the northern Lower Peninsula. It is seen less frequently in the metropolitan area of southeast Lower Michigan and in the intensively farmed Thumb region. Most Michigan bluebirds migrate south in winter, but a few southern Michigan residents stay here during mild winters.
From mid-February to mid-March, bluebirds return to Michigan in small flocks from southern wintering grounds. Early nesters, they begin to look for woodpecker holes and cavities, which they will clean out if necessary.
Bluebirds are extremely territorial, and will often fight over nest cavities. Males typically show several potential sites to females, who will make the final decision. Males may mate with more than one female, and females may mate with more than one male.
Once the female selects a cavity, she spends a week or so bringing soft, dry grass with which to form a deep, cup-shaped nest inside the cavity. She will then lay a clutch of three to six eggs, with five eggs being the standard. For the next 12 to 14 days she will incubate the eggs. Once hatched, the nestlings will remain in the box for about two weeks. Therefore, bluebirds need four to five weeks of uninterrupted time to rear their young.
Both sexes aid in feeding the young, and they stay with the juveniles for several days after the fledglings leave the nest. The adults may raise one or two more families during the summer-long nesting season before they head south again for the winter.
Food and Water
Bluebirds like to perch on telephone and electrical wires from which they prey on grasshoppers, crickets, beetle and other insects, which make up about two-thirds of their diet. Bluebirds are also attracted to mowed lawns where they catch ground-hugging insects. During fall migration and on its winter range, fruiting vines, shrubs, and trees are favored.
Although bluebirds do not winter in Michigan in large numbers, they may be found in wetlands where they feed on sumac, wild grapes, pokeweed, honeysuckle, poison ivy, and holly. Bluebirds do not migrate long distances, and when food abounds in mild winters, they go no farther south than is necessary. Bird feeders containing a mixture of peanut butter and cornmeal may also attract them in winter.
Like most birds, bluebirds are attracted to water. Bluebirds like to bathe nearly every day and sometimes several times daily. Therefore, the presence of an abundance of water is important in their survival.
Since bluebirds are territorial, your land will only support a limited number of bluebird pairs. They will usually not nest within 100 yards of each other. Keep this in mind when measuring the success of your management.
Oak savannas, oak barrens, and jack-pine barrens are good examples of native habitat important to bluebirds. Generally, bluebirds do best where soils are either very dry or very wet. Trees have a difficult time becoming established in these areas, and the scattered trees that result often make good nesting sites for bluebirds.
Habitat manipulation should be minimal in these types of areas, although fire management can be beneficial in oak savannas, oak barrens, and jack-pine barrens where it can be safely executed by fire management professionals (permits are usually required). In other areas, such as abandoned orchards and old fields, more active management may be needed.
The following are options to consider when managing for bluebirds:
Building and Placing a Nest Box
Materials: Use 1/2 inch or 3/4 inch wood such as cedar or exterior-grade plywood. Treat pine or other wood on the outside only to protect it from the weather. If you paint the box, use a drab color such as gray, green or tan, which will help the box to blend into surroundings and help protect it from overheating. Do not use pressure-treated wood, which contains copper arsenate. Use 1-inch coated box nails or wood screws. The box may be nailed, screwed or wired to metal poles, fence posts, private utility poles or tree trunks.
Design: The outside dimensions of the box should be 5-1/2 inches wide and 15 inches tall in back. The body of the box is placed two inches from both the top and the bottom of the backboard. The bottom should be recessed a quarter-inch, and the inside corners cut away to provide drainage. Make the entrance hole 1-1/2 inches in diameter, and do not provide a perch on the box, which will attract sparrows and other undesirable birds. Install a predator guard (as shown below) around the entrance that will prevent predators from disturbing the nest.
Access: You need to be able to get into the box to clean it out after each clutch, or to remove nests of wasps and other birds. The design in our diagram allows for the side to pivot outward. Some box builders prefer access from the front or top of the box.
Mounting: Using holes placed in the extensions of the back, secure the box four to six feet above the ground. Metal poles provide better protection against predators, or you can place a collar of sheet metal 18 inches wide just below the box if necessary. If ants invade the box, greasing the mounting pole will prevent them from climbing. You can also place the box on a fence post.
Location: Locate the box in an open field area with plenty of insects but in an area where pesticides are not being used. The boxes should be placed away from buildings and near perches. If possible, mount it along a field edge near wires or other perches. If you place the box too close to trees and shrubs, though, house wrens will likely invade. Boxes placed near gardens may result in bluebirds helping to control garden insects.
Place two boxes 15 to 25 feet apart and at least 100 yards from the next pair of boxes. Pairing boxes allow tree swallows (or other territorial birds) to use one box and leave the empty one for bluebirds. Artificial nest boxes should be erected and ready by mid-February. Expect chickadees, titmice, sparrows, woodpeckers, wrens, and flying squirrels to also use the boxes.
Wrens and sparrows are a special problem because they will evict bluebirds and destroy their nests. If the box is filled with unorganized twigs, a wren has likely moved in. Assuming the wren is not nesting, remove the twigs and plug the hole until the wren relocates. Then, consider mounting a wren box with 1-inch diameter hole near shrubbery, or move the bluebird box farther from shrubbery.
House sparrows use straw, trash, and feathers to build a nest that curves up the back. Look for other clues such as missing or pierced eggs, and pecked or dead nestlings lying under the box. An option is to move bluebird boxes away from buildings and bird feeders. Because sparrows are not protected by law, they can be destroyed.
Crows, jays, and grackles are other birds that prey on bluebird eggs and young. Solutions are to increase the roof overhang or deepen the box. To control wasps and bees, first remove their nests, then rub bar or liquid soap on the box ceiling. A predator guard will discourage raccoons, squirrels, and house cats.
Providing nesting, foraging, and watering sites is essential to attracting bluebirds to your property. Bluebird trails and cooperative projects with neighbors are an excellent way to build a population of bluebirds and associated species in your area.
Last Revised: December 12, 1999