Eastern Bluebird Natural History

The brilliant blue male bluebird has a rusty throat, breast and sides, and white belly. He sits high atop a dead tree or branch, TV antenna, or power line to hunt for insects that make up two-thirds of his diet. He and his mate also eat wild berries, especially in cold weather when insects are not available. They rarely damage cultivated crops and are very beneficial to farmers and gardeners by eating insects. The young bluebirds have spotted breasts until fall molt.

As early as the end of February and as late as June, the male bluebird locates a nesting site, establishes territory around it of two to five acres, and sings to attract a female and warn other male bluebirds to stay away. Once a female accepts the site, she builds a neat cup-shaped nest of dry grasses and pine needles. Nest building may take five days to three weeks.

The female lays one blue, or rarely white, egg each morning until three to six eggs are produced. The female begins incubating the eggs after the final egg is laid. Thirteen to fourteen days later, all eggs will hatch with hours of each other.

The adults begin feeding the young immediately after hatching, starting with soft insects and graduating to courser food as the nestlings grow. The adults also keep the nest clean by removing the fecal sacs that enclose the nestlings’ waste. The nestlings grow very rapidly, with their eyes opening on about the eighth day. By the time the nestlings fledge (leave) the nest box 16 – 20 days after hatching, they will be nearly the size of an adult bluebird.

Usually, the entire brood of fledglings leaves the box within two hours. The fledglings can fly fifty to one hundred feet on their first flight and try to land in a bush, shrub or low branch to avoid predators. The adults continue to care for the young and teach them to forage for food. The male bluebird will continue this job while the female begins her second or third nest. On occasion, the young from a first nesting will help feed the nestlings from their parents’ second or third nesting.

After nesting season is over, bluebirds give up their territories and flock together. South Carolina bluebirds do not migrate. They are joined by migrant northern bluebirds and roam the area looking for berries. In winter, bluebirds will roost in pine tree stands and nest boxes to avoid cold weather.

Why Do Bluebirds Need Our Help?

Between the 1920’s and the 1970’s, the bluebird population declined by an estimated 90%. There are a number of reasons for this but the main ones are loss of habitat and competition from other species.

Loss of Habitat

The bluebird is a cavity nesting bird, which means it prefers to build its nest in a tree cavity. Unlike the woodpecker, however, the bluebird’s beak is no suited for excavating. It depends on natural cavities, or ones made by other birds. However, the expansion of large commercial or agricultural operations, growth of cities and dense residential land development have destroyed many of the bluebirds’ natural nesting places.


The main source of competition for bluebirds is a bird that is not native to North America – the House or English Sparrow. The House Sparrow was introduced to this country in the mid 1800’s. It was thought that this bird would help control insect pests; however, those that brought them here seriously underestimated this bird’s fiercely competitive nature. The House Sparrow population exploded, while that of the bluebird declined alarmingly. While House Sparrows will nest about anywhere they can find a nook or cranny, they compete with the more finicky bluebird, and will often drive away adult bluebirds, leaving bluebird nestlings to starve to death. Worse, they will also peck open unhatched bluebird eggs and kill the babies, or even adults they happen to find sitting on the nest. They have even been known to build their own nests on top of the bodies of the bluebirds they have killed. Another source of competition for the bluebird is the Eastern Starling, a bird that is equally aggressive and will also kill both bluebird adults and young.


Photo by Andrew Lydeard

What Can You Do?

Birdhouses are readily available, but not everything called a “bluebird house” is really suitable for them. Real bluebird conservation takes a bit of effort, but it is well worth it when you see your first brood of fledglings take flight. Several things to keep in mind when you decide to put up a nest box for bluebirds are:

Suitable Location

Bluebirds prefer to nest in an area that includes open space, scattered trees, and low ground cover such as lawns, golf courses, pastureland, parks and school & industrial campuses. They do not nest in heavily forested areas. They also do not like land that is completely open (no trees or shrubs), but one that still provides perches for hunting (such as fences, telephone lines, posts, shepherd’s hooks, etc.) and trees nearby for both shade and to offer the baby birds a safe destination for fledging. Care should be taken not to place the nest box so close to trees and fences, which  predators are afforded easy access to the box from above. Keep boxes at least 200 yards from barnyards and feed lots where House Sparrows are abundant. Avoid areas with heavy pesticide use. Bluebirds are territorial, so multiple boxes should be placed at least 100 feet apart as a rough guide. Vegetation and topography might make closer location possible. There should be no direct line of sight between multiple boxes.

Proper Nest Box

Purchase or build a nest box designed specifically for bluebirds. Preferably, these are made of unpainted cedar, redwood, cyprus or pine. If you must paint your nest box, it should be painted ONLY on the outside, in a very light color, to avoid overheating. The box should have an overhanging slanted roof, NO perch, and a round entrance hole 1-1/2″ in diameter. It should have ventilation and drainage holes, be deep enough so predators can’t reach in to get to the eggs, and have a door that opens for ease of monitoring and cleaning. In areas of intense heat, additional measures should be taken to avoid overheating, such as the use of 3/4″ lumber, and overhanging roof on all sides, and placement in a location that receives shade from the afternoon sun.

Proper Mounting

Nest boxes may be mounted at any time, but to attract bluebirds for their first nesting of the season, they should be in place by mid-March, depending on your geographic location. You may see nest boxes mounted on trees, wooden fence posts or metal poles. SCBS highly recommends mounting nest boxes on a metal or plastic pole with a predator baffle to deter critters such as snakes and raccoons:”

Metal poles may be difficult for predators such as snakes and raccoons to climb. A metal mounting post need not be elaborate or expensive. Smooth, round 1″ electrical conduit is inexpensive and works well; although any smooth scrap round pipe will work. The next box should be mounted on the post so that the entrance hole is 5 feet off the ground.


Monitoring Nest Boxes

Being a conscientious bluebird landlord involves more than simply buying or making a nest box and mounting in in a good location. Nest boxes should be monitored at least once a week to be sure that undesirable competitors are not sing them. They should also be monitored for blowflies, ants, and other parasites, and predator problems. Bluebirds readily tolerate humans monitoring their nest boxes. They will not abandon their young because humans have looked at or touched them. Bluebirds do not have a good sense of smell, so your scent on their nest will not disturb them.Care should always be taken when opening a nest box, especially once the hatchlings are 12 days old, as this could cause them to fledge too early. The nest box should be cleaned out after each brood of babies has fledged. Bluebirds will not reuse a nest. They will typically produce three broods of three to six young by from March to August in South Carolina.

Photo by Mike deBruhl

Feeding Bluebirds

It is not normally necessary to feed bluebirds; however, many people find they enjoy offering treats to their birds, both to help them through times of difficulty, and to have the opportunity to interact more closely with these gentle, trusting creatures. They eat insects and insect larvae and berries. Some common native berry bushes that bluebirds enjoy are: Flowering Dogwood, Holly, Juniper, Sumac, Mountain-ash, Mistletoe, Hackberry, and Firethorn. Another food commonly offered to bluebirds is mealworms. They can be purchased in bulk from several mail-order houses, or obtained locally at bait shops, and wild bird supply stores. During the winter months, bluebirds will come to suet feeders and seed feeders containing sunflower meats. One caution is if you like to feed other species of birds – do not place your bluebird nest boxes too close to your wild bird feeding area. Feeding seed “blends” containing corn, milo, and millet, or feeding stale bread, rolls or donuts will attract house sparrows to your yard, and endanger your bluebirds. Bluebirds also enjoy shallow birdbaths, especially those with a drip/misting feature.