Anhinga anhinga
anhinga

The northernmost distribution of Anhinga anhinga leucogaster is in the United States from North Carolina to Texas. It has however been spotted as far north as Wisconsin. Its range also includes Mexico, Central America, Panama, and Cuba. The individuals found in the more northern areas of the U.S. migrate there in March and April and stay until October, then return to Mexico and more southern parts of the U.S. Anhinga anhinga anhinga is found in South America from Colombia to Ecuador, east of the Andes to Argentina, and in Trinidad and Tobago. The range is limited by cool temperatures and low amounts of sunshine. (del Hoyo, Elliot, and Sargatal, 1992; Hennemann, 1985; Isenring, 1997)

Anhinga anhinga prefers freshwater and coastal aquatic habitats that include shrub or tree-covered islands or shores; these habitats include lakes, marshes, swamps, mangrove swamps, shallow coastal bays, and lagoons. Within such habitats, anhingas are able to stalk slow-moving prey and seek refuge from danger in the water, and perch and sun itself in the treetops. (del Hoyo, Elliot, and Sargatal, 1992; Owre, 1967)

Anhingas have an average body length of 85 cm, weight of 1350 g, wingspan of 117 cm, and bill length of 81 mm. The head is small and appears to be merely an extension of its long snake-like neck. In the neck, the 8th and 9th cervical vertebrae create a hinge-like apparatus that allows the quick catching of prey. The long, sharp, serrated bill also aids it in hunting. The wings are broad, allowing it to soar, and the feet are webbed to facilitate swimming. The physical structure of the legs is, however, more suited to crawling out of water onto land and for climbing bushes and trees. The tail is long and is used for providing lift, steering, braking, and balancing. When spread in flight, the tail resembles that of a turkey. The overall body shape of anhingas resembles that of a cormorant; the hunting action of the head and neck is more similar to a heron.

Anhingas are sexually dimorphic; males have brighter colors than females. Males have greenish-black plumage overall, accentuated by silver-gray feathers on the upper back and wings that are edged with long white plumes. They also have black crests. Females are brown with a lighter brown head and neck; juveniles are a uniform brown color. Molting of all flight feathers at the same time render them flightless for a while. Unlike some aquatic birds, all of the body feathers become completely wet upon contact with the water, allowing them to dive through the water more easily. This feature, however, causes them to have little buoyancy, to lose heat quickly, and hinders flight. (del Hoyo, Elliot, and Sargatal, 1992; Hennemann, 1982; Owre, 1967; Scott, 1983)

Anhingas start flight by either running on the surface of the water or diving from a tree. They usually return to the water by gliding into it from a perch or crawling into it from land. Only the head and neck are visible when in the water due to their low buoyancy. Most of the time spent in the water is devoted to fishing; otherwise they are found perched in trees. Often they crawl from the water and then up to a high perch in order to sun themselves. Similar to cormorants and turkey vultures, anhingas sun themselves by spreading out the wings, which dries out the plumage and absorbs heat from the sun. Anhingas lose heat quickly in the water due to their lack of an insulating layer of body feathers; thus, the sun's radiation helps them maintain body temperature. Anhingas are solitary but are sometimes found among groups of herons, cormorants, ibises, or storks. Although they nest in small loose groups, it is unusual to find them with other anhingas at other times of the year. (Burger, Miller, and Hahn, 1978; del Hoyo, Elliot, and Sargatal, 1992; Hennemann, 1982)

Normally quiet birds, vocalizations include clicks, rattles, croaks, and grunts. Anhingas typically call while on or near the nest, and occasionally while flying or perching. They are particularly silent and elusive when flightless due to molting. (Burger, Miller, and Hahn, 1978; del Hoyo, Elliot, and Sargatal, 1992; Hennemann, 1982)

Anhingas prey primarily on fish (Percidae, Centrarchidae, Peociliidae, Cyprinodontidae), but their diet can also include aquatic invertebrates and insects. Although not particularly fast swimmers, they are effective aquatic hunters, relying on their quick necks and sharp bills to catch prey. They target slower-moving species of fish and stalk them underwater, finally striking out with their long neck and spearing the prey with the beak. They then bring the prey above water and manipulate it in order to swallow the fish head first. (Owre, 1967)

In North America, anhingas have no particular economic impact, particularly since they do not eat the fish that humans might. (del Hoyo, Elliot, and Sargatal, 1992)

Anhingas and their eggs are eaten by humans in parts of Asia. (del Hoyo, Elliot, and Sargatal, 1992)

In the Americas, anhingas are abundant, although their aquatic habitats are threatened. DDT was found to have an effect on the reproductive success of these birds and banning of this pesticide in North America has benefited those birds that breed in the southern United States. (del Hoyo, Elliot, and Sargatal, 1992)

Although anhingas resemble cormorants (Phalacrocorax species), the two have several differences. Cormorants are more powerful swimmers and thus able to hunt faster-swimming fish, whereas anhingas are much slower in the water and hunt slower-swimming fish. Anhingas are able to soar, but require gliding flights from trees in order to start flight, unlike cormorants, which are not able to soar and can easily take off from the water. Anhinga distributions are more limited by temperature due to their low metabolic rate. Cormorants are able to maintain higher body temperatures and are found in colder regions of North America. Also, anhingas use a flap and glide form of flight, whereas cormorants continually flap. (Owre, 1967)