Anhinga anhinga [an' hin guh an' hin guh]

Description

This large bird with a long S-shaped neck and a long pointed bill has an average body length of 33 inches, a wingspan of 46 inches, and weighs just under 3 pounds. The head is small and appears to be merely an extension of its neck. The wings are broad, allowing it to soar, and the feet are webbed to facilitate swimming. The physical structure of the legs allows the bird to come onto land and climb 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 the anhinga resembles that of a cormorant, but the hunting action of the head and neck is more similar to a heron.

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 renders them flightless for a while. Unlike other 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.

Distribution and Habitat

There are two geographically distinct subspecies of anhinga. The northernmost distribution of Anhinga anhinga leucogaster is found in the United States from North Carolina to Texas, although it has 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 United States migrate there in March and April and stay until October, then return to Mexico and more southern parts of the United States. 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.

Both subspecies prefer 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.

Feeding Habits

Anhingas prey primarily on fish, 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.

Reproduction

Breeding can occur throughout the year, but is usually triggered by wet or dry seasons.

The male begins courtship by soaring and gliding, followed by marking a possible nest location with leafy twigs. Then he performs behavioral displays to attract the female. Once the pair is formed, the male gathers nesting material, while the female builds a platform nest, which is usually on a branch overhanging water or in open areas in the tops of trees. The female constructs the nest by weaving sticks together and padding it with live twigs and green leaves. Males defend any threats to nesting territories with extensive displays and even fighting. Females are less aggressive, but will defend the nest if necessary. Once formed, breeding pairs are monogamous, and may reuse nests from year to year.

The female lays one egg every one to three days, until she has a clutch of two to six eggs; average clutch size is four eggs. The oval-shaped eggs are bluish-white or pale green, sometimes with brown speckles. Both parents share in incubating the eggs for 25 to 30 days.

Upon hatching, anhinga chicks are naked and helpless. They eventually grow a white down on their belly side and a dark down on their back side. At first the parents feed the chicks by dripping fluid and regurgitated material from partially digested fish down their throats. As the chicks grow older, they shove their heads down the parents' beaks to get this food material. The chicks are in the nest approximately three weeks, but if threatened, are able to drop into the water and swim away, later climbing out of the water and back into the nest. At the end of three weeks, they are able to climb out of the nest to a branch, and fledge at approximately six weeks. They stay with their parents for several more weeks before becoming independent.

Anhingas can live up to 16 years in the wild.

Other Information

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.

When not fishing, anhingas are usually found perched in trees.

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 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.

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.

Scientific Classification

phylum Chordata
subphylum Vertebrata
class Aves
order Pelecaniformes
family Anhingidae
genus & species Anhinga anhina

Animal Diversity Web http://animaldiversity.org/accounts/Anhinga_anhinga/

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