Preferred Diets of Birds Preferred Dlet Type of Bird American goldfinch Eastern bluebird Lesser goldfinch Purple martin Yellow warbler Seeds from grasses and wildflowers A large variety of insects Seeds from sunflower plants Winged insects Caterpillars, moths, mosquitoes, and beetles O Purple martin and yellow warbler Eastern bluebird and purple martin O Lesser goldfinch and eastern bluebird O American goldfinch and lesser goldfinch​