Eastern Bluebirds

A male Eastern Bluebird

    Eastern Bluebirds (Sialia sialis) are one of three species of bluebirds in North America. This includes its close relative the Western Bluebirds (Sialia mexicana) out west (which they can hybridize with where their ranges overlap), and the Mountain Bluebirds (Sialia currucoides) in the mountainous regions of the West with its hovering flight (which can also hybridize with the Eastern though much less commonly do so). They are all members of the thrush (Turdidae) family of birds. 

    Eastern Bluebirds are between 6.5 to 7 inches in size and are the most widespread of the three species, including ranging as far south as Nicaragua and the eastern half of the U.S and Canada. However, until the 1970’s bluebirds were in severe decline. The loss of nesting cavities and competition from invasives such as house sparrows and European starlings were the main reasons for these declines. In 1978, the North American Bluebird Society was formed and along with its efforts, bluebirds started to recover. 

    One of the ways that helped most was building proper bird boxes to fill in for missing tree cavities that bluebirds traditionally used and reducing competition from other birds such as house sparrows and European starlings. There are numerous boxes available for sale and you can build your own as well with plans available on the internet. One of the most important things to remember is keep the entrance hole no bigger than 1 ½ inches to keep starlings and larger birds out. 

    Next is proper placement. Bluebirds prefer edges and open habitats with native plants in a meadow or edge setting, and, if possible away, from buildings. Native plants are extremely important as pretty much all the food for the young will be insects and these insects evolved together with the native plants. Nonnative and especially invasive plants will Not supply the necessary amount of insects to allow the young to fledge. A nearby small tree or sapling is often good to allow not only the bluebirds a place to keep an eye on the nest but for the first flights for the young. Placing the bird box on a steel pole and then placing a predator baffle (such as a metal cone guard) around the pole to keep raccoons, snakes and other predators from accessing the nest works best. Keep it away from overhanging trees or fences that the predators can use to gain access or drop down onto the bird box as well. Cat/raccoon guards made of mesh placed around the entrance hole so it is difficult for these predators to reach inside is always a good idea. 

A bluebird box complete with predator baffles.

     House sparrows can be an issue, so if placing the bird box well away from buildings doesn’t help, you can construct a scare baffle that helps keep sparrows away made from monofilament line, and using PVC pipe entrances (sometimes referred to as a Gilbertson design) also works well. If they still persist, just recall that invasive house sparrows are not protected by law and the eggs can be removed. Boxes are often placed 200 feet apart, but some place them close together or even next to each other in the belief that if tree sparrows use one and bluebirds the other, they can both combine to drive off predators. 

    Many more tips and information on the things mentioned can be obtained by contacting your local bluebird society website and on the internet. Bluebirds will also roost in these boxes in the winter as well, so they can be useful year-round.

A female Eastern Bluebird brings nesting material into a bird box in Barcroft Park, Arlington, VA. Note the cat/raccoon guard at the front of the box entrance.

    Eastern Bluebirds can have 2-3 broods a year. They lay 3-6 pale blue eggs each time. These take 16-21 days to incubate and the young fledge after 16-21 days. Occasionally bluebirds will lay their eggs into other bluebird’s nest, particularly if there are not enough nest cavities present. Female bluebirds will also occasionally mate with more than one male, and so the male which helps feed the young may not always be feeding its own young. Eastern bluebirds are short to intermediate migrants. As they feed their young insects and prefer these for themselves, when the cold weather kills these food items off, they need to find other food sources or move south. They form winter flocks which can number over 200 and search for additional items to feed on. They often search for berries and fruits to tide them over, particularly liking wild grapes. They may also come to bird feeders that are stocked with mealworms, raisins, berries, and peanut butter mixes. 

    Bluebirds were significant in many native American cultures. They were symbols of spring for many tribes. For the Haudenosaunee (Iroquois) the singing of blue birds were said to drive off winter. The Cherokee associated them with the wind and thought they could influence the weather. To the Pueblo, the bluebirds were sons of the sun. To the Pima, bluebirds are a symbol of transformation. One of their legends says that bluebirds got their color from by bathing in magical blue water, originally being the color of clay and considering itself ugly. It took 4 days of daily bathing for the feathers to turn blue. Many clans are named after bluebirds in their own languages such as clans in the Pueblo, Hopi, and Diné (Navajo). 

    So please keep an eye out for bluebirds or listen to their songs (which many people think sounds like “Tru-ly , Tru-ly”) and perhaps encourage them into your yards using some of the information here.