The Eastern Bluebird is a small, migratory thrush whose survival depends on a diverse diet that shifts dramatically with the changing seasons. Its ability to locate specific high-protein or high-energy foods is directly tied to its reproductive success and winter survival. This adaptability requires the bluebird to switch from a primarily insect-based diet in the summer to one centered on wild fruits when invertebrates become scarce.
The Breeding Season Staple: Insects and Arthropods
During the spring and summer months, the Eastern Bluebird’s diet consists of up to two-thirds insects and other small invertebrates. This high-protein intake is necessary to support the energy demands of reproduction and the rapid growth of their young. Bluebirds primarily hunt by perching on an elevated spot, such as a wire or tree branch, and scanning the ground below for movement. Once prey is spotted, the bird employs a “perch-and-pounce” technique, quickly dropping down to capture the item on or near the ground. Their diet is rich in common garden and field invertebrates, including grasshoppers, crickets, various beetles, soft-bodied moth and butterfly larvae, spiders, and earthworms.
Winter Survival: Native Fruits and Berries
With the arrival of cooler weather, the bluebird’s food source shifts significantly as insects become inactive or die off. The bird must transition to a diet of wild fruits and berries to obtain the calories and energy needed to maintain body temperature during winter. Their preference is for native, soft-flesh fruits that remain on the branches throughout the cold season. The bird seeks out specific berries from plants such as sumac, dogwood, holly, and eastern red cedar. They also readily consume the berries of poison ivy and Virginia creeper, which are often overlooked by other wildlife. A specific adaptation allows the bluebird to extract nutrients from these plants by digesting the soft pulp while passing the hard seeds completely undigested. This process aids in the dispersal of native plant seeds across the landscape.
Specialized Needs of Nestlings
The dietary needs of bluebird nestlings are highly specialized, requiring an almost exclusive supply of soft, easily digestible, high-protein invertebrates. For the first several days after hatching, parents concentrate on feeding the young soft-bodied items, such as small caterpillars and spiders. This type of food provides the necessary protein and moisture for rapid development without straining the nestlings’ undeveloped digestive systems. Parents will bring whole, non-regurgitated food directly to the nestlings, with feeding frequency being extremely high. While earthworms are occasionally fed to older nestlings, they must be used sparingly because they can sometimes cause digestive distress or diarrhea in young birds.
Supplemental Foods Provided by Humans
Humans can offer supplemental foods to Eastern Bluebirds, particularly during the harsh winter months or the demanding breeding season. The single most popular and readily accepted item is the mealworm, which can be offered live or freeze-dried, providing a concentrated source of protein. Specific types of suet can also be offered, especially those blended with peanut butter or berries, as they provide fat and energy. Avoid suet made with rendered beef fat; bluebirds rarely consume traditional birdseed mixes. Foods such as bread, cracked corn, or large seeds should not be offered. These items provide little nutritional value and can attract aggressive bird species, like House Sparrows, which compete with bluebirds for resources.