The Purple martin is the largest swallow in North America. Despite their name, these birds are not truly purple. Their dark blackish-blue feathers have an iridescent sheen caused by the refraction of incident light giving them a bright blue to navy blue or deep purple appearance. In some light, they may even appear green in color. Adult males are entirely black with glossy steel blue sheen, the only swallow in North America with such coloration. Adult females are dark on top with some steel blue sheen and lighter underparts. Adults have a slightly forked tail.
Purple martins breed across eastern North America, and also some locations on the west coast from British Columbia to Mexico. In winter, these birds migrate to the Amazon basin. Purple martins inhabit open areas near wetlands, swamps, and wet meadows. They can be found along forest edges, in mountain forests, shrubland, agricultural areas, farms, and in urban settlements.
Purple martins are diurnal social birds; they live and breed in colonies but prefer forage in small groups or in pairs. These birds are agile hunters and eat a variety of winged insects. They primarily feed by hawking, a strategy of catching insects in the air during flight. Rarely, they will come to the ground to eat insects. Purple martins migrate to North America in the spring to breed. Older males typically migrate first and leave the overwintering sites in late December or early January, followed by older females. Younger birds (first yearlings) typically arrive at the breeding grounds up to two months later. When the breeding season is over, Purple martins head south. Some birds leave as early as July and others stay as late as October. Martins generally migrate over land, through Mexico and Central America. When not breeding, martins form large flocks and roost together in great numbers. This behavior begins just prior to the southern migration and continues on the wintering grounds. Purple martins are fairly noisy, chirping, and making sounds that can be described as chortles, rattles, and croaks. The various calls are said to be "throaty and rich" and can be rendered as tchew-wew, pew pew, choo, cher, zweet and zwrack. The males have a gurgling and guttural courtship song, a dawn song, and even a subsong used at the end of the breeding season.
Purple martins are serially monogamous and form pairs that last within one nesting season. However, they may also exhibit polygynous behavior when one male may mate with more than one female. Breeding season occurs during May and June. Males arrive in breeding sites before females and establish their territory. A territory can consist of several potential nest sites. After forming a pair, both the male and female inspect available nest sites. Purple martins make their nests in cavities, either natural or artificial. In many places, humans put up real or artificial hollow gourds or houses for martins. The nest is made inside the cavity of such artificial structures and retains a somewhat flat appearance. The nest is a structure of primarily three levels: the first level acts as a foundation and is usually made up of twigs, mud, small pebbles, and even small river mollusk shells; the second level of the nest is made up of grasses, finer smaller twigs; the third level of construction composing the nest, is a small compression usually lined with fresh green leaves where the eggs are laid. Purple martins generally produce only a single brood. The average clutch size is 4 to 6 eggs per nest. Incubation lasts 15-16 days and the female is the main incubator, with some help from the male. Fledging, when the young leave the nest, occurs between 26-32 days after hatch day. The chicks will continue to receive care from both parents for up to a month after fledging and become reproductively mature at 1 year of age.
Purple martins suffered a severe population crash in the 20th century that was caused by the release and spread of European starlings in North America. European starlings and house sparrows compete with martins for nest cavities; they also kill adult martins, take over the nest and remove eggs or remaining young. Where Purple martins once gathered by the thousands, by the 1980s they had all but disappeared. Today, these birds are experiencing a unique threat to their long-term survival. Nearly all eastern species exclusively nest in artificial gourds and ‘condo’ units provided by human ‘landlords’. A practice that has been experiencing a steady decline in the number of ‘landlords’ offering nesting sites. One study found that nearly 90% of landlords were 50 years of age or older, and that younger generations were not exhibiting the same enthusiasm nor possess the resources to provided martin housing for the species.
According to the What Bird resource, the total population size of the Purple martin is 11,000,000 individuals. According to the All About Birds resource the total population size of the species is 7 million birds. Overall, currently, Purple martins are classified as Least Concern (LC) on the IUCN Red List and their numbers today remain stable.
Purple martins feed mainly on various insects and play an important role as pest controllers. Thee birds also serve as food items for local predators such as hawks, starlings, owls, gulls, crows, snakes, raccoons, herons, squirrels, and house cats.