Anhingas (darters)

 

The Anhingidae family of birds is closely related to other families within the Sulae suborder, which includes gannets, boobies, cormorants and shags. However, the four species that comprise the Anhingidae show several features that set them apart from birds such as the cormorant to which they might, at first sight, appear to be similar.

 

The four species are the anhinga or American darter (Anhinga anhinga), the Oriental or Indian darter (Anhinga melanogaster), the African darter (Anhinga rufa) and the  Australasian or Australian darter (Anhinga novaehollandiae). They are long, slim water birds that inhabit tree-lined margins of freshwater lakes and rivers in tropical and warm temperate regions, only rarely being found in brackish waters. Their regional distributions are suggested by their names, but the differences between the species are not all that great. Indeed, they can almost be thought of as four subspecies of a widely distributed species, the anhinga or darter, which is also sometimes called the snakebird. Another name used in the United States is water turkey, which is strange in that any presumed resemblance to a turkey must be the product of a very vivid imagination! However, this may have something to do with the anhinga’s appearance on the Southern table as meat.

 

The anhinga is between 32 and 36 inches in length, which makes it similar in size to a cormorant, but their heads are slimmer, their bills longer and thinner and unhooked, their necks longer, and their body feathers thicker. Males and females are differently coloured, unlike cormorants. However, one feature that anhingas have in common with cormorants is that their flight feathers are relatively permeable to water, so they need to spread their wings to dry after they have been swimming. They also lack air sacs under the skin and have quite heavy bones, which is an aid when diving.

 

Female anhingas tend to be slightly larger than the males, but with smaller bills. Males have generally dark plumage with the females being lighter in colouring.

 

Anhingas are strong fliers, with steady and rapid wingbeats, but they glide and climb more than cormorants. They can sometimes be seen riding warm air currents several hundred feet up, with wings outstretched and necks and legs extended, thus forming a cross shape.

 

Anhingas from the northern part of their North American range will fly south for the winter, which is when they are sometimes found in more brackish waters.

 

Anhingas only enter the water to escape from danger or to feed. They can swim completely underwater, with nostrils closed, or with the body submerged and only the head and neck above the surface. This latter mode is what gives them the “snakebird” epithet.

 

The name “darter” is equally well deserved, as this refers to the bird’s method of catching their prey. The neck will be held in an S-shape and the rapier-like beak thrust suddenly forwards to spear a fish. This is then brought to the surface, tossed in the air, caught again and swallowed whole. Other prey includes frogs and salamanders, which are speared and then beaten to death against a rock. Crayfish and water insects also form part of the diet.

 

Anhingas nest in small colonies, often alongside ibises and herons. A bulky nest of sticks, lined with green leaves, is built in a bush or tree, anything from three to thirty feet above the water. The average clutch size is four eggs, although this can be as few as two or as many as six. Incubation, by both parents, can take up to four weeks, after which the chicks are fed by food regurgitated by a parent bird.

 

The chicks are born blind and naked, but are able to leave the nest when two weeks old, should the need arise. If danger threatens, a chick is able to fall into the water and swim ashore, although they are then very vulnerable to predators such as alligators. A chick can climb back to the nest by using its wings and neck as well as its feet.

 

Young anhingas fledge at six to eight weeks, staying close to the nest until they are ready.

© John Welford