The purple martin is the largest swallow in North America. Males are all dark, glossy blue-black; females and immatures duller above and grayish below. The purple martin is an extremely popular and well-known bird due to its willingness to nest in structures provided by humans. Polytypic. Length 7.5" (19 cm).
Identification Adult male: all glossy blue-black above and below, wings and tail dusky black, distinctly notched tail. In hand, small concealed white tuft on sides of rump and sides of body are visible. Adult female: duller above than male, with more scattered patches of blue-black above. Grayish collar on hind neck. Throat, breast, and flanks dusky brown, paler on center of belly. Undertail coverts grayish with dusky centers. Immature: similar to adult female; young males show some blue-black on head and underparts, dark shaft streaks on ventral feathers, and sometimes a less distinct collar on hind neck; females, paler below and browner above, and lack dusky centers on undertail coverts. Flight: somewhat starlinglike shape. Graceful, liquid wingbeats interspersed with gliding and soaring.
Geographic Variation Females of western (arboricola) and desert (hesperia) subspecies with whiter underparts and forehead. Immature males tend to look more like females of eastern subspecies (subis).
Similar Species Very similar to, sometimes indistinguishable from, other martins except the brown-chested. Female purple martin is the only species with contrasting gray collar on hind neck and pale forehead. Mottled undertail coverts.
Voice Call: most frequently gives a chur call in many situations. When alarmed or excited, gives a zwrack or zweet call. Song: usually a series of chortles, gurgles, and slightly harsher croaking phrases. Also gives a churring, chortling “dawn song” around potential nest sites upon arriving on the breeding grounds in early spring.
Status and Distribution Fairly common but a local and declining summer resident. Breeding: in the East, colonially almost exclusively in artificial sites near human habitations. In the West, frequently solitarily, more often in natural cavities in forested areas, and in saguaro cactus in desert Southwest. Nest: in cavity excavated by another species, or in artificial structures; 3–6 eggs (late March–late May). Migration: in spring, arrives as early as mid-Jan. in Texas, Florida, and Gulf Coast; early March in Virginia and Kansas, mid-April in southern Canada, May in Arizona, early May in Montana. During fall, in the East, very large aggregations of thousands of birds form locally in late summer. Passage peaks late July–September, beginning as early as late May, with stragglers until early October. In Southwest, scarce August–late September. Winter: South American lowlands east of the Andes south to northern Argentina (rarely) and southern Brazil. Vagrant: accidental in Bermuda and United Kingdom.
Population Causes of long-term declines unknown. Competes for nest cavities with the introduced European starling and house sparrow. In the West, logging has reduced availability of natural nest cavities. Increased availability of human-provided nest sites has had a positive effect on populations. Sharp declines in southern California.
—From the National Geographic book Complete Birds of North America, 2006