Very few birds share the same brilliant attire, cheerful persona, and backyard-friendly reputation as the Eastern Bluebird (Sialia sialis). Found in lawns across the Eastern United States, they are a much-loved favorite of many bird enthusiasts.
These birds hardly need description, as most of us could recognize them in an instant. Males are a vibrant blue with a striking orange breast and stark white belly. Females look identical except they are markedly paler. The Eastern Bluebird is one of three bluebird species in the United States. It shares the country with its western counterparts – the Western Bluebird (Sialia mexicana) and Mountain Bluebird (Sialia currucoides). Their song is a series of genial whistles and chatters, and the call is a wavering “tu-a-wee.” Being a member of the Thrush family (Turdidae), they are closely related to another familiar backyard bird – the American Robin (Turdus migratorius). Though the adults look different, the close relationship between robins and bluebirds is why fledglings of both species share a similar speckled appearance.
While bluebirds are a backyard staple nowadays, they were not always so common. Their populations had begun seriously declining as early as the 1920s because of alterations in land use. Urbanization, forest fragmentation, reduction of natural open spaces, fire suppression, forest thinning (i.e. clearing dead material that could serve as nesting sites), and use of pesticides all contributed to a drop in bluebird numbers. The negative effects of these changes were compounded by invasive species and predation. European Starlings (Sturnus vulgaris) and House Sparrows (Passer domesticus) are extremely aggressive nonnative birds. They compete for nesting cavities, often driving away or even killing breeding bluebirds. To top it off, an extremely severe ice storm in 1978 reduced vital food sources, further dropping bluebird numbers. Populations declined so drastically in some regions that several state wildlife agencies declared the species as rare. Sadly, many of the threats that Eastern Bluebirds faced throughout the 20th century persist today. However, the introduction of nest box programs has helped to combat these declines.
The North American Bluebird Society has been a major player in the bluebird’s recovery by encouraging nationwide public involvement in bluebird conservation. Due to extensive efforts over the past decades, citizen-run nest box initiatives have restored bluebird populations. Tennessee, Virginia, and North Carolina all have active bluebird organizations. Local chapters are working to maintain regional bluebird numbers and educate community members about cavity nesting bird conservation. NestWatch, a Cornell Lab of Ornithology platform, also promotes citizen-powered support for breeding birds. Check out the NestWatch and North American Bluebird Society websites to get started with building boxes and monitoring your own bluebirds.
In East TN, Southwest VA, and Western NC, the bluebird breeding season begins around late March and lasts until mid-August. Eastern Bluebird females typically construct their nests out of pine straw in an artificial or natural cavity. Once the nest cup is fully formed and lined with soft grasses, she lays 3-5 sky-blue eggs. Sometimes other colors are laid – approximately 4-5% of females lay white eggs. After several weeks of incubation and brooding, the young fledge from the nest. The male continues feeding the fledglings while the female begins working on another clutch. It is common for bluebirds in our area to lay a second and occasionally even a third brood. The older fledglings sometimes stick around to help raise the new nestlings. Talk about built-in babysitting!
The Eastern Bluebird is primarily insectivorous. Bugs make up almost 70% of their diet. Caterpillars, grasshoppers, spiders, beetles, and everything in between are on the menu for the bluebird. It has been said that they can catch up to 2,000 insects a day. That equates to nearly 350,000 insects over a single breeding season. Hunting small insect prey requires excellent eyesight. They can spot a creepy crawly from over 50 yards away. For reference, that is half the length of a football field! Berries like viburnum, sumac, dogwood, mulberry, pokeweed, holly, etc. make up the rest of their diet. When insects are scarce in winter, they rely almost entirely on these plants. Dried mealworms are also a tasty snack that birdwatchers can provide at feeders. However, too many mealworms can deplete a bluebird’s calcium, so be sure to provide recommended amounts as supplemental feeding only.
These stunning birds are truly a joy to observe. Becoming a bluebird landlord is fun, interesting, and a great way to contribute to a successful, decades-old conservation initiative. Consider putting up a nestbox this season and watch the fascinating life of our Eastern Bluebird unfold from the comfort of your own home.