Although eastern bluebird populations are on the rise, the largest threat to their future is the continued loss of nesting habitat. Approximately two-thirds of the diet of an adult eastern bluebird consists of insects and other invertebrates. The remainder of the bird's diet is made up of wild fruits. Favored insect foods include grasshoppers, crickets, katydids, and beetles. Other food items include earthworms, spiders, millipedes, centipedes, sow bugs, and snails.
Fruits are especially important when insects are scarce in the winter months.
Some preferred winter food sources include dogwood, hawthorn, wild grape, and sumac and hackberry seeds. Supplemental fruits eaten include blackberries, bayberries, fruit of honeysuckle, Virginia creeper, red cedar, and pokeberries. Bluebirds feed by perching on a high point, such as a branch or fence post, and swooping down to catch insects on or near the ground. The availability of a winter food source will often determine whether or not a bird will migrate. If bluebirds do remain in a region for the winter, they will group and seek cover in heavy thickets, orchards, or other areas in which adequate food and cover resources are available.