darter

Anhingidae are large birds with sexually dimorphic plumage. They measure about 80 to 100 cm (2.6 to 3.3 ft) in length, with a wingspan around 120 cm (3.9 ft), and weigh some 1,050 to 1,350 grams (37 to 48 oz). The males have black and dark-brown plumage, a short erectile crest on the nape and a larger bill than the female. The females have much paler plumage, especially on the neck and underparts, and are a bit larger overall. Both have grey stippling on long scapulars and upper wing coverts. The sharply pointed bill has serrated edges, a desmognathous palate and no external nostrils. The darters have completely webbed feet, and their legs are short and set far back on the body. There is no eclipse plumage, but the bare parts vary in color around the year. During breeding, however, their small gular sac changes from pink or yellow to black, and the bare facial skin, otherwise yellow or yellow-green, turns turquoise. The iris changes in color between yellow, red or brown seasonally. The young hatch naked, but soon grow white or tan down.

Ofter swims with head and neck above the water and body below. Seensingly, in scattered pairs and sometimes in larger groups. Spends much timedrying its spread wings and tail while sitting on a favoured perch. Unlike commorants does not leap up before diving, but slowly sumberges. Lakes ponds. reservoirs, rivers, marches and other inland waters; also mangroves and coastal waters.

Darters feed mainly on mid-sized fish; far more rarely, they eat other aquatic vertebrates and large invertebrates of comparable size. These birds are foot-propelled divers which quietly stalk and ambush their prey; then they use their sharply pointed bill to impale the food animal. They do not dive deep but make use of their low buoyancy made possible by wettable plumage, small air sacs and denser bones. On the underside of the cervical vertebrae 5–7 is a keel, which allows for muscles to attach to form a hinge-like mechanism that can project the neck, head and bill forward like a throwing spear. After they have stabbed the prey, they return to the surface where they toss their food into the air and catch it again, so that they can swallow it head-first. Like cormorants, they have a vestigial preen gland and their plumage gets wet during diving. To dry their feathers after diving, darters move to a safe location and spread their wings. Darters go through a synchronous moult of all their primaries and secondaries making them temporarily flightless, although it is possible that some individuals go through incomplete moults.

Darter vocalizations include a clicking or rattling when flying or perching. In the nesting colonies, adults communicate with croaks, grunts or rattles. During breeding, adults sometimes give a caw or sighing or hissing calls. Nestlings communicate with squealing or squawking calls.

It has a long and slender neck with a straight pointed bill and like the cormorant it hunts for fish while its body submerged is in water. It spears a fish underwater bringing it above the surface tossing and juggling it before swallowing the fish head first. The body remains submerged as it swims and the slender neck alone is visible above the water which accounts for the colloquial name of snakebird. Like the cormorants it has wettable feathers and it is often found perched on a rock or branch with its wings held open to dry. The adult plumage above is black and the wing coverts and tertials having silvery streaks along the shaft. The crown and neck are brown shading to black towards the back of the neck. The underparts are blackish brown. A pale line over the eye and throat and a line running along the sides of the neck gives it a striped appearance. The iris is white with a yellow ring (brighter yellow in breeding birds) around it. The tip of the upper mandible is dark while the base is pale brown bill while the lower mandible is yellowish. The legs and webbing on the foot are yellow in immatures and non-breeding birds while breeding birds have darker grey tarsi and toes with yellow webbing. The sexes are not easily distinguishable but males tend to have black speckles that coalesce on the white throat. Adult females have a shorter bill and tend to have the black at the base of neck and chest separated from the hind neck by a wide buff band that ends at the shoulder.