About two thirds of an adult bluebird’s diet consists of insects and other invertebrates. The remainder is made up of wild fruits or berries. The bluebird’s preferred insect prey include grasshoppers, crickets, katydids, and beetles. Other prey include earthworms, spiders, millipedes, centipedes, sow bugs, and snails.
In the breeding season, males tip their heads back and fluff up feathers to display and keep other males away. This same behavior is used as a defensive posture to attempt to intimidate predators. Male common grackles are less aggressive toward one another, and more cooperative and social, than the larger boat-tailed grackle species.