It takes two years for both males and females to attain their adult plumage, but they can and do breed as one year olds. Adult males that are two years old and older have glossy, purple-black plumage. Adult females are less colorful, with gray necks, foreheads, and underparts, but they can be nearly as purple on their backs as adult males. Yearling males resemble adult females but can be distinguished by a few distinct purple feathers on the chin, throat, breast, and flanks. Yearling females are less colorful than yearling males and are white underneath.
Juveniles are gray brown with grayish white underparts.
While martin populations have grown in the East, their numbers have declined in the middle of the United States. This species nests in open and semiopen areas, including savannas, cultivated lands, fields, parks, pastures, near lakes and marshes and in towns and suburbs. In the West, martins are less likely to inhabit nest boxes, relying more heavily on natural cavities, but they will nest in gourds and supplied single-unit houses on the West Coast. They also feed on midges, dragonflies, damselflies, cicadas, stinkbugs, beetles, and butterflies. They are not the mosquito specialists that martin-house manufacturers would have us believe.