Putting up a purple martin (Progne subis) house is like installing a miniature neighborhood in your backyard. In the East, dark, glossy-blue males and brown females will peer from the entrances and chirp from the rooftops all summer. In the West, martins mainly still nest the old-fashioned way—in woodpecker holes. Our largest swallows, purple martins perform aerial acrobatics to snap up flying insects. At the end of the breeding season they gather in big flocks and make their way to South America.