Anhinga Life History

Habitat

The Anhinga lives in shallow, slow-moving, sheltered waters and uses nearby perches and banks for drying and sunning. It's rarely found out of freshwater except during severe droughts. Generally not found in extensive areas of open water, though it may nest on edges of open bays and lakes. Breeds in association with other waterbirds such as herons, egrets, ibises, storks, and cormorants. The Anhinga may also breed in saltwater colonies and feed in freshwater.

Food

The Anhinga's diet consists of many small- to medium-sized wetland fishes, with very small amounts of crustaceans and invertebrates. It swims slowly underwater, stalking fish around submerged vegetation. Anhingas typically spear fish through their sides with a rapid thrust of their partially opened bill. They usually stab with both mandibles, but may use the upper mandible only on small fish. The side-spearing habit of the Anhinga suggests that the usual hunting method is by stalking rather than pursuit.

Nesting

Nest Placement

The Anhinga typically nests in loose groups of several to hundreds of pairs, and sometimes with other colonial waterbirds. The nest is usually in a tree near to water or overhanging it.

Nest Description

The male begins nest construction before he has a mate, by placing large sticks and green material in the forks of trees. The male collects nearly all the nesting material, and the female then finishes building. The nest is a bulky platform of sticks, somewhat more compact than heron nests. It is often lined with fresh leaves, green twigs, willow leaves, and catkins. Over time, excrement can build up on the outer rim of the nest giving it a white appearance.

Nesting Facts

Behavior

The Anhinga swims lower in the water than many other birds due to its reduced buoyancy-a result of wetted plumage and dense bones. When at the surface, it tends to swim low in the water, often with only the neck and head above the water, and sometimes with only the bill exposed. The Anhinga is also an adept soarer. While soaring, it holds its wings flat and straight, its neck outstretched or held with a slight kink; its long, straight tail is conspicuous. Anhingas often use thermals for soaring, and may achieve altitudes of several thousand feet.

Conservation

A relatively accurate estimate of the Anhinga population is difficult to obtain because the birds are uncommon throughout their range and reside in areas that can be difficult to reach. According to the North American Breeding Bird Survey, however, populations increased by close to 2% per year between 1966 and 2019. Partners in Flight estimates Anhinga’s global breeding population at 2 million and rates them 9 out of 20 on the Continental Concern Score, indicating a species of low conservation concern. Potential threats to Anhingas include the development of wetlands which may reduce available habitat for Anhinga. Discarded fishing lines also pose a threat because the birds can get tangled up in them.

Credits

Frederick, Peter C. and Douglas Siegel-Causey. (2000). Anhinga (Anhinga anhinga), version 2.0. In The Birds of North America (P. G. Rodewald, editor). Cornell Lab of Ornithology, Ithaca, New York, 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). Avian Conservation Assessment Database, version 2020.

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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