Boat-tailed Grackle Life History

Habitat

Boat-tailed Grackles breed abundantly in salt and freshwater marshes along the Atlantic and Gulf coasts. They are closely associated with saltwater and are rarely found more than about 30 miles from saltwater except in the Florida peninsula, where they occur across its breadth. Main breeding habitats include saltmarsh; marshes along rivers, lakes, impoundments, or ponds; and nearby upland habitats. They forage in city streets and plazas, cultivated fields, stockyards, open beaches, and saltmarshes. They stay in the same types of habitats during the nonbreeding season.Back to top

Food

Boat-tailed Grackles eat arthropods, crustaceans, mollusks, frogs, turtles, lizards, grain, seeds, fruit, and tubers. Inveterate scavengers and pirates, they also take food from humans, domestic animals, and other birds. They usually forage out in the open, in a wide variety of habitats that include floating mats, mudflats, beaches, roadsides, parking lots, dumps, cultivated fields, and cattle feedlots. They walk slowly over the ground or in shallow water, pecking or probing at soil, litter, or low vegetation. They often overturn debris, stones, and shells with their bills. In aquatic habitats they stand still and cock their heads to watch the water with one eye, then plunge their heads below the surface. They can pry open mussel shells and eat snails by forcing an opening between the tissue and the shell. Boat-tailed Grackles often dunk foods like bread, rice, and dog food in water before eating them.Back to top

Nesting

Nest Placement

Boat-tailed Grackles nest in cattails and other grasses of freshwater or brackish marshes, about 2 feet off the ground. Females choose an area secure from ground predators and out of the reach of floodwaters. Especially in the northern part of their range, they may nest in isolated trees or bushes near water, up to 13 feet off the ground. Nest trees include live oak, white mangrove, wax myrtle, redcedar, water oak, and cabbage palm.

Nest Description

The female builds the nest by herself in about 8 days, starting with a shallow platform of long, coarse grass stems, leaves, or Spanish moss. On top of the platform she weaves an outer cup of grass stems and leaves around branches, and then adds an inner layer of wet mud and debris to create an inner cup about 3.5 inches across and just as deep. Finally she lines the nest with fine materials like pine needles and grass stems.

Nesting Facts

Behavior

Gregarious Boat-tailed Grackles roost communally in tall grasses all year round. During the breeding season, the nesting females stay on their nests, but males and nonbreeding females leave colonies to join roosts that may include other blackbirds and European Starlings. The harem mating system of these grackles is unique to birds in North America, though it’s shared by oropendolas of the American tropics. Individual males defend clusters of nesting females from other males. Only the high-ranked males, having established their status through displays and vigorous fights, get to mate in the colony, although DNA evidence indicates other males manage to mate with females away from the colonies. Boat-tailed Grackles often take advantage of humans for food and predator protection, through behavior like foraging in dumpsters and forming colonies on traffic islands. Their most serious predators are the yellow rat snakes that attack their nests, but they are also preyed upon by black rats, Norway rats, rice rats, alligators, and Purple Gallinules.Back to top

Conservation

Boat-tailed Grackles are fairly common within their restricted range, but populations declined by about 47% between 1966 and 2014, according to the North America Breeding Bird Survey. Partners in Flight estimates the global breeding population at 2 million, with 100% living in the United States. They rate a 10 out of 20 on the Continental Concern Score and are not on the 2014 State of the Birds Watch List. Their strict habitat use of marshes along a very narrow coastal range puts them at risk from coastal development, which is intense in many areas. Researchers recommend monitoring their numbers and maintaining coastal impoundments for nesting birds. Some people consider Boat-tailed Grackles to be pests because they are gregarious and noisy, their droppings are messy, and they may eat pet food, rice crops, and fruit-tree crops. People sometimes try to deter grackles and other blackbirds by shooting at them, or poisoning them (although Boat-tailed Grackles are legally protected under the Migratory Bird Treaty Act of 1918). In some places farmers have adopted less harmful methods of protecting their crops, including cutting down brushy roost sites, harvesting while grackles are busy nesting, and scaring the birds away with balloons or explosions.Back to top

Credits

Bancroft, G. T. (1984a). Growth and sexual dimorphism of the Boat-tailed Grackle. Condor 86: 423–432.

Lutmerding, J. A. and A. S. Love. (2020). Longevity records of North American birds. Version 2020. Patuxent Wildlife Research Center, Bird Banding Laboratory 2020.

North American Bird Conservation Initiative. (2014). The State of the Birds 2014 Report. US Department of Interior, Washington, DC, USA.

Partners in Flight (2017). Avian Conservation Assessment Database. 2017.

Post, William, J. P. Poston and G. Thomas Bancroft. (2014). Boat-tailed Grackle (Quiscalus major), version 2.0. In The Birds of North America (P. G. Rodewald, editor). Cornell Lab of Ornithology, Ithaca, New York, USA.

Sauer, J. R., J. E. Hines, J. E. Fallon, K. L. Pardieck, Jr. Ziolkowski, D. J. and W. A. Link. The North American Breeding Bird Survey, results and analysis 1966-2013 (Version 1.30.15). USGS Patuxent Wildlife Research Center (2014b). Available from http://www.mbr-pwrc.usgs.gov/bbs/.

Sibley, D. A. (2014). The Sibley Guide to Birds, second edition. Alfred A. Knopf, New York, NY, USA.

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