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. A. anhinga anhinga is found in South America from Colombia to Ecuador, east of the Andes to Argentina, and in Trinidad and Tobago. The Anhinga's range is limited by cool temperatures and low amounts of sunshine. (del Hoyo et al. 1992, Henneman 1985, Isenring 1997)

A. 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, A. anhinga is able to stalk slow-moving prey and seek refuge from danger in the water, and perch and sun itself in the treetops. (Owre 1967, del Hoyo et al. 1992)

A. anhinga has 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 this 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 of A. anhinga resembles that of a cormorant; the hunting action of the head and neck is more similar to a heron.

A. anhinga is dimorphic; the male has brighter colors than the female. The male has greenish-black plumage overall, accentuated by silver-gray feathers on the upper back and wings that are edged with long white plumes. It also has a black crest. 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 it flightless for a while. Unlike some aquatic birds, all of A. anhinga's body feathers become completely wet upon contact with the water, allowing it to be able to dive through the water more easily. This feature, however, causes it to have little buoyancy, to lose heat quickly, and hinders flight. (del Hoyo et al. 1992, Henneman 1982, Owre 1967, Scott 1983)

A. anhinga starts its flight by either running on the surface of the water or diving from a tree. It usually returns 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 its low buoyancy. Most of the time spent in the water is devoted to fishing; otherwise it is found perched in trees. Often it crawls from the water and then up to a high perch in order to sun itself. Similar to cormorants and turkey vultures, A. anhinga suns itself by spreading out its wings, which allows it to dry out the plumage and absorb heat from the sun. A. anhinga loses heat quickly in the water due to its lack of an insulating layer of body feathers; thus, the sun's radiation helps it to maintain its body temperature.

A. anhinga prefers to stay on its own, but at times is found among groups of herons, cormorants, ibises, or storks. Although it does nest in small loose groups with its species, it is unusual to find it with other anhingas. Normally a quiet bird, its vocalizations include clicks, rattles, croaks, and grunts. It typically calls while on or near the nest, and occasionally while flying or perching. It is particularly silent and elusive when flightless due to molting. (Burger et al. 1978, del Hoyo et al. 1992, Henneman 1982)

A. anhinga preys primarily on fish (family Percidae, Centrarchidae, Peociliidae, Cyprinodontidae), but its diet can also include aquatic invertebrates and insects. Although not a particularly fast swimmer, it is an effective aquatic hunter, relying on its quick neck and sharp bill to catch prey. It targets slower-moving species of fish and stalks them underwater, finally striking out with its long neck and spearing the prey with its beak. It then brings the prey above water and jerks it off its bill, manipulating it in order to swallow the fish head first. (Owre 1967)

In North America, A. anhinga has no particular economic impact, particularly since it does not eat the fish that humans might.(del Hoyo et al. 1992)

Both the eggs and birds of the Anhinga genus are eaten by humans in parts of Asia. (del Hoyo et al. 1992)

In the Americas, A. anhinga is abundant, although as with many bird species, their habitat is 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 U.S. (del Hoyo et al. 1992)

Although A. anhinga resembles the cormorant (Phalacrocorax spp.), the two have several differences. The cormorant is a more powerful swimmer and thus able to hunt faster-swimming fish, whereas the Anhinga is much slower in the water and therefore hunts slower-swimming fish. A. anhinga is able to soar, but requires gliding flights from trees in order to start flight, unlike the cormorant that is not able to soar and can easily take off from the water. The Anhinga is more limited by temperature due to its low metabolic rate, and thus, it is disposed to a more southern range in North America. The cormorant, however, is able to maintain a higher body temperature and able to deal with colder temperatures, explaining their range in colder regions of North America. (Owre 1967)