American Bittern Life History

Habitat

American Bitterns breed mainly in freshwater marshes with tall vegetation. You can find them in wetlands of many sizes and kinds, typically less densely vegetated and shallower than wetlands used by the Least Bittern. In winter they move to areas where water bodies don't freeze, especially near the coast, where they occasionally use brackish marshes. Managed wetlands such as wildlife refuges seem to be important for wintering American Bitterns. Wintering birds may also forage in dry grasslands and other terrestrial habitats.Back to top

Food

American Bitterns eat insects, crustaceans, fish, amphibians, reptiles, and small mammals. Their most common insect prey include water striders, giant water bugs, water beetles, water scorpions, grasshoppers, and especially dragonflies, which the birds sometimes manage to capture in midair. Frequently consumed fish include eels, catfish, pickerel, sunfish, suckers, perch, killifish, and sticklebacks. Rayfish, crabs, frogs, tadpoles, salamanders, garter snakes, water snakes, and meadow voles round out the diet. American Bitterns usually forage in dim light, at shorelines and the fringes of vegetated areas. A foraging bird may sway its neck, perhaps to see past glare from the surface of shallow water, or to warm up its muscles for a quick strike. A characteristic strategy is to stand stock-still with bill held horizontal, gradually aiming the bill downward with nearly imperceptible movements—until, with a sudden darting motion, the bittern seizes the prey in its bill, bites or shakes it to death, and swallows it head first. Indigestible parts of prey animals are regurgitated as pellets.Back to top

Nesting

Nest Placement

American Bitterns usually build their nests among thick stands of cattails, bulrushes, and sedges that grow out of shallow water. Less commonly, they nest on dry ground, in grassland areas dense with tall herbaceous plants. Limited research suggests that the females choose the nest sites.

Nest Description

The female American Bittern gathers materials, builds the nest, incubates eggs, broods, and feeds chicks with no apparent assistance from the male. She builds a mound or platform about 3.5 to 8 inches above the water’s surface, using dead, dry reeds, sedges, cattails, or other vegetation, and lines the nest with fine grasses. The nest’s outside diameter ranges from about 10 to 15 inches.

Nesting Facts

Behavior

American Bitterns are solitary foragers, standing motionless or walking slowly with outspread toes in search of food. They hunt during the day and especially at dawn and dusk. Possibly the most famous aspect of bittern behavior is the stance it assumes when it perceives a threat. It points its bill skyward, elongates its body, and even sways with the breeze, all to blend in with its reedy surroundings. This pose is so ingrained that bitterns sometimes adopt it even when they’re out in the open. American Bitterns don't do much socializing apart from migrating in small groups, mating, and facing off over territories—which can be dramatic. Competing males hunker down and approach each other while displaying white plumes between their shoulders. This can escalate into an airborne chase, with the combatants spiraling upwards, trying to stab each other with their bills. A male about to copulate lowers and pumps his head, and fluffs the white feathers that usually lie concealed beneath his wings. Copulation lasts about 15 seconds. Males and females have little to do with each other apart from copulation, although a female may nest near a "booming" male as a way of distracting predators from her brood. Back to top

Conservation

American Bitterns are fairly common, but their numbers declined in some regions of the U.S. and Canada between 1966 and 2019, according to the North American Breeding Bird Survey. Partners in Flight estimates a global breeding population of 2.5 million and rates them 12 out of 20 on the Continental Concern Score, indicating a species of relatively low conservation concern. These reclusive birds are difficult to survey accurately; regions of the Northeast and Upper Midwest have declined significantly, although estimates of decline for the continent, as a whole, are small. With its entire life cycle dependent on wetlands, the bittern’s fate is inextricably linked to that of its frequently degraded or developed habitat. More than half the original wetlands in the lower 48 states have already been destroyed, and inland freshwater wetlands—the American Bittern’s most important nesting and wintering grounds—are among the most threatened. Coupled declines of the bittern and its habitat were recorded in Massachusetts as early as the 1890s. The American Bittern was listed in 1982 and 1987 as a Nongame Species of Management Concern by the U.S. Fish and Wildlife Service, with listed causes including habitat loss, human disturbance, and exposure to pesticides and pollutants. Marshland invasion by exotic plant species may also affect habitat suitability, as can siltation, overgrowth of plants, and oxygen depletion due to contamination with nutrients, and other forms of pollution that affect the birds or their prey.

Credits

Dunne, P. (2006). Pete Dunne's essential field guide companion. Houghton Mifflin Harcourt, New York, USA.

Gibbs, J. P., S. Melvin, and F. A. Reid. 1992. American Bittern. In The Birds of North America, No. 18 (A. Poole, P. Stettenheim, and F. Gill, Eds.). Philadelphia: The Academy of Natural Sciences; Washington D.C.: The American Ornithologists' Union.

Kushlan, J. A., M. J. Steinkamp, K. C. Parsons, J. Capp, M. A. Cruz, M. Coulter, I. Davidson, L. Dickson, N. Edelson, R. Elliott, R. M. Erwin, S. Hatch, S. Kress, R. Milko, S. Miller, K. Mills, R. Paul, R. Phillips, J. E. Saliva, W. Sydeman, J. Trapp, J. Wheeler and K. Wohl (2002). Waterbird conservation for the Americas: The North American waterbird conservation plan, version 1. Washington, DC, USA.

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

Partners in Flight (2020). Population Estimates Database, version 3.1.

Sauer, J. R., D. K. Niven, J. E. Hines, D. J. Ziolkowski Jr., K. L. Pardieck, J. E. Fallon, and W. A. Link (2019). The North American Breeding Bird Survey, Results and Analysis 1966–2019. Version 2.07.2019. USGS Patuxent Wildlife Research Center, Laurel, MD, USA.

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

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