The scientific classification of the eastern bluebird is Passeriformes (order), Turididae (Thrush) family, Sialia (genus), and sialis (species). Male bluebirds have a bright blue back and tail, rusty colored breast, and a white abdomen. The females have blue wings and tail with a gray-brown back, rusty breast and grayish-white abdomen. Their size from head to tip of tail is about 5 ½ inches. The blue and rust coloration makes both sexes easy to identify in the field.
Bluebird species. The eastern bluebird does not share its range with either the mountain or western bluebirds. The western bluebird (Sialia mexicana) has a blue throat and a rusty upper back, while the mountain bluebird (Sialia currucoides is sky blue with no rust on a bluish breast. The mountain bluebird lives in higher altitudes in the same range as the western bluebird.
Habitat Preference
Bluebirds prefer short ground cover such as pastures, golf courses, and lawns instead of woods. They need natural cavities and seem to prefer old woodpecker nests; however, they will also use nest boxes which have the correct size entry hole. Bluebirds will not nest in dense woods or near high brush. This has contributed to their declining populations since other cavity nesting birds simply retreated further into the woods as habitat is destroyed.
Distribution
Bluebirds are only found in North America. The eastern bluebird breeds east of the Rockies, from the Canadian Provinces down to the central portion and the eastern coastal region of Mexico and northern Central America.
Courtship Behavior
Males generally arrive in the nesting area two or three days to two weeks earlier than the females. The male finds possible nesting locations, sings to entice the female to enter his territory, and offers her food such as caterpillars. He will fight off any intruders that invade his territory during courtship.
Females appear to ignore the male during his courtship ritual. The female indicates her acceptance of the male by inspecting one of the nesting sites. The male responds to her action with much singing and flying displays such as the “butterfly flight” and “wing-waving”. Once the female begins nest building she will fight violently with, and may even kill female intruders.
Males respond to female fighting in one of two ways. He may try to physically separate them, in which case the females fly away and resume their fight until one bird leaves the area. Alternatively, he may accept both females and raise two families in close proximity to each other.
Nesting Behavior
Nesting periods. Researchers suggest that natural selection favors those birds that nest earliest in the season since nest sites become scarcer later in the season. Birds that nest early have time to raise two families if the first attempt should fail. Predators are also scarcer during the early spring nesting period.
Nest location. The nest may be located either in naturally occurring cavities, in nest boxes, or in former woodpecker nests. Bluebirds are known as secondary cavity nesters because they do not excavate their own nest. The nest is constructed from dried grasses, pine needles, and other plant materials.
Egg laying and incubation. The female lays one egg a day until the clutch, ranging from two to seven eggs, is completed. The eggs average .8 inches long and .6 inches wide. They are a clear blue with no other markings.
Incubation generally lasts 13-14 days although it may last longer if the weather is cool and damp. The female begins incubating after the last egg is laid. This results in all the eggs hatching at nearly the same time. The female leaves the nest only to find food. During that time the male bird will enter the nest box but doesn’t appear to do actual incubation. He may feed the female during incubation but not enough that she could survive only on him as a food source.
Nestling care. Nestlings are feed every 20 minutes. One day old nestlings are fed spiders (higher in calories than insects). Two to five day old nestlings are fed spiders and butterfly or moth larva. Older nestlings are given beetles, earthworms, crickets, grasshoppers and other foods typically used by adults. Fruit is also eaten.
Bluebirds normally leave the nest at 13-14 days. The fledglings fly to the nearest tree, fence, or anything else that keeps them off the ground on their first flight from the nest. The parents continue to feed then for about 10 days. The male takes over the feeding process when the fledglings have been out of the nest for about 10 days. During this time they learn to catch their own prey.
The male bluebird completely takes over the feeding process if the female begins a second nest. If the pair raises at least one nest safely, the male-female pair bond normally lasts throughout the season. Second nests fail more if the birds have safely raised a first nest. This may be due to physiological strain of raising the first nest.
Behavior Patterns
Bluebirds will remain with their parents and the fledglings of successive nestlings during their first summer. Several family groupings will gather in loose flocks during the summer to feed. These same flocks migrate south together in the fall. The actual timing of the migration seems to be determined by weather and food availability.
Food Preferences/Methods of Feeding
Food. Bluebirds vary their diet according to the season, weather and temperature. During the spring, summer, and fall, insects form the largest percentage of their diet. Bluebirds feed on both animals and plants. Among their favored animal food items are: caterpillars, crickets, moths, horseflies, beetles, millipedes, grubs, earthworms, and termites. Bluebirds feed on staghorn sumac, multiflora roses, honeysuckle, cherry, and mulberry. They may also eat seeds from pokeberry, Japanese honeysuckle, possumhaw seeds, rose seeds, and sumac during cold weather.
Methods of feeding. The bluebird uses its binocular vision to locate prey from their lookout perch (a tall tree or pole). They then drop to the ground to catch it. Since they frequently change lookout perches, it is necessary that good bluebird habitat contain an abundance of dead trees, telephone poles, fence posts, etc., that can serve as these lookout perches.
Bluebirds may also capture aerial insects (flycatching), remove prey from plant foliage (gleaning), and hop on the ground to search for food. They also hover in the air or perch on tree limbs while consuming fruit.
Bluebird Mortality
Bluebird nestlings die from many causes. Among them are parasites (blowfly larva is a common one), snakes, starlings, house wrens, and raccoons. Adult bluebirds face several causes of death. Among these are exceptionally cold winters, food limitation, various diseases, and natural enemies such as cats, raccoons, squirrels, and snakes.
Bluebird mortality in nest boxes may be improved by creating them in shapes more closely resembling natural cavities. The bluebirds themselves create problems by filling the nest box with so much plant material that the distance between the top of the nest and the entry hole is so short that predators have an easy time in reaching the nestlings. It is important that nest boxes are cleaned out annually to eliminate part of this problem.
Habitat Management Practices
Bird enthusiasts that want to provide bluebird habitat need to provide housing, food, water, and protection from predators. Since bluebirds prefer old woodpecker nests for their nesting sites, any dead trees on the edge of woods near open meadows or lawns should be left standing. Pesticides should not be used.
The homeowner should choose from the following plants to provide optimum food for bluebirds.
Red chokeberry (Aronia arbutifolia), Spicebush (Benzoin aestivale), Bittersweet (Celastrus scandens), Hackberry (Celtis occidentalis), Flowering dogwood (Cornus florida), Small-leaved cotoneaster (Cotoneaster microphylla), Washington hawthorn (Crataegus phaenopyrum), Blackthorn (Crataegus tomentosa), Inkberry (Ilex glabra(), Smooth winterbeery (Ilex laevigata), American holly (Ilex opaca), Black sider (Ilex verticillata), Western red cedar (Juniperous scopulorum), Red cedar (Juniperus virginiana), Privet (Ligustrum vulgare), Amur honeysuckle (Lonicera maacki), Moonseed (Menispermum candense), Bayberry (Myrica carolinensis(), Sour gum (Nyssa sylvatica), Virginia creeper (Parthenoclassus quinquefolia), Pyracantha (Pyracantha species), Sumacs ( Rhus species), Multiflora roses (Rosal multiflora), Mountain ash (Sorbus Americana), Coralberry (Symphoricarpos orbicalatus), and the various Viburnums (Viburnum species).
Many of the above mentioned plants are wonderful ornamental plants for the landowner as well as being an excellent food source for bluebirds and other bird species.
What Can You Do To Help Bluebirds?
Humans have contributed to a slight upswing in bluebird populations by following suggestions provided by the North American Bluebird Society. Visit their website for more information. You may want to consider joining the society.
