The Boat-tailed Grackle is a large, conspicuous blackbird (subfamily Icterinae) found along the coasts of eastern North America. The species was first described in 1819 by the French ornithologist Louis Jean Pierre Vieillot from a specimen collected in New Orleans, Louisiana. The easily recognized, pigeon-sized male is loud, with a long tail and iridescent blue-green plumage. The less conspicuous, cinnamon-colored female is half the size of the male and, to a casual observer, appears to be a different species.
This grackle is an opportunistic omnivore that eats foods ranging from seeds and insects to crabs and lizards. In many areas it has established a commensal relationship with humans; by doing so, it may increase its rate of food intake and gain protection from predators.
The Boat-tailed Grackle's mating system (harem polygyny) appears to be unique among North American songbirds but has been found in the oropendolas (Psarocolius) of the American tropics. Boat-tailed Grackle sexes remain apart most of the year, except in the nesting season when females gather in large, dense colonies, usually on small islands in marshes or in isolated trees in settled areas. Many males are attracted to each nesting colony, but only a few high-ranked individuals succeed in mating there. Relative positions in the male dominance hierarchy are maintained from year to year; the alpha male may be ten years or older. Despite the high mating success of alpha males within the nesting colony proper, a high percentage of young are sired by noncolony males.
The reproductive behavior of female Boat-tailed Grackles is molded by the potentially high rate of predation occurring in marshes. Females nest synchronously in predator-safe sites such as marsh islands patrolled by alligators, or in trees in highway traffic islands. Their incubation and nestling periods are shorter than in other similar-sized songbirds. Young leave the nest prematurely, and weight gain is sacrificed for early maturation of legs and plumage.
Little is known about the complex vocal repertoire of this species. Its song and Precopulatory Vocalization are of particular interest because of the role they may play in maintaining reproductive isolation from the very similar Great-tailed Grackle (Quiscalus mexicanus), which is expanding its range into areas occupied by the Boat-tailed Grackle.