Змеешейки: Биология и Особенности Семейства Anhingidae.

Family of birds

The darters, anhingas, or snakebirds are mainly tropical waterbirds in the family Anhingidae, which contains a single genus, Anhinga. There are four living species, three of which are very common and widespread while the fourth is rarer and classified as near threatened by the IUCN. The term snakebird is usually used without any additions to signify whichever of the completely allopatric species occurs in any one region. It refers to their long thin neck, which has a snake like appearance when they swim with their bodies submerged, or when mated pairs twist it during their bonding displays. "Darter" is used with a geographical term when referring to particular species. It alludes to their manner of procuring food, as they impale fishes with their thin, pointed beak. The American darter (A. anhinga) is more commonly known as the anhinga. It is sometimes called "water turkey" in the southern United States; though the anhinga is quite unrelated to the wild turkey, they are both large, blackish birds with long tails that are sometimes hunted for food.

Anhingidae are large birds with sexually dimorphic plumage. They measure about in length, with a wingspan around , and weigh some 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. 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. 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.

Predators of darters are mainly large carnivorous birds, including passerines like the Australian raven (Corvus coronoides) and house crow (Corvus splendens), and birds of prey such as marsh harriers (Circus aeruginosus complex) or Pallas's fish eagle (Haliaeetus leucoryphus). Predation by Crocodylus crocodiles has also been noted. But many would be predators know better than to try to catch a darter. The long neck and pointed bill in combination with the "darting" mechanism make the birds dangerous even to larger carnivorous mammals, and they will actually move toward an intruder to attack rather than defending passively or fleeing.

They usually breed in colonies, occasionally mixed with cormorants or herons. The darters pair bond monogamously at least for a breeding season. There are many different types of displays used for mating. Males display to attract females by raising (but not stretching) their wings to wave them in an alternating fashion, bowing and snapping the bill, or giving twigs to potential mates. To strengthen the pair bond, partners rub their bills or wave, point upwards or bow their necks in unison. When one partner comes to relieve the other at the nest, males and females use the same display the male employs during courtship; during changeovers, the birds may also "yawn" at each other. These birds reach sexual maturity by about two years, and generally live to around nine years. The maximum possible lifespan of darters seems to be about sixteen years. Darter eggs are edible and considered delicious by some; they are locally collected by humans as food. The adults are also eaten occasionally, as they are rather meaty birds (comparable to a domestic duck); like other fish eating birds such as cormorants or seaducks they do not taste particularly good though. Darter eggs and nestlings are also collected in a few places to raise the young. Sometimes this is done for food, but some nomads in Assam and Bengal train tame darters to be employed as in cormorant fishing. With an increasing number of nomads settling down in recent decades, this cultural heritage is in danger of being lost. On the other hand, as evidenced by the etymology of "anhinga" detailed below, the Tupi seem to have considered the anhinga a kind of bird of ill omen. Anhinga is derived from the Tupi ajíŋa (also transcribed áyinga or ayingá), which in local mythology refers to a malevolent demonic forest spirit; it is often translated as "devil bird". The name changed to anhingá or anhangá as it was transferred to the Tupi–Portuguese Língua Geral. However, in its first documented use as an English term in 1818, it referred to an Old World darter. Ever since, it has also been used for the modern genus Anhinga as a whole. This family is very closely related to the other families in the suborder Sulae, i. e. the Phalacrocoracidae (cormorants and shags) and the Sulidae (gannets and boobies). Cormorants and darters are extremely similar as regards their body and leg skeletons and may be sister taxa. In fact, several darter fossils were initially believed to be cormorants or shags (see below). Some earlier authors included the darters in the Phalacrocoracidae as subfamily Anhingina, but this is nowadays generally considered overlumping. However, as this agrees quite well with the fossil evidence, some unite the Anhingidae and Phalacrocoracidae in a superfamily Phalacrocoracoidea. The Sulae are also united by their characteristic display behavior, which agrees with the phylogeny as laid out by anatomical and DNA sequence data. While the darters' lack of many display behaviors is shared with gannets (and that of a few with cormorants), these are all symplesiomorphies that are absent in frigatebirds, tropicbirds and pelicans also. Like cormorants but unlike other birds, darters use their hyoid bone to stretch the gular sac in display. Whether the pointing display of mates is another synapomorphy of darters and cormorants that was dropped again in some of the latter, or whether it evolved independently in darters and those cormorants that do it, is not clear. The male raised wing display seems to be a synapomorphy of the Sulae; like almost all cormorants and shags but unlike almost all gannets and boobies, darters keep their wrists bent as they lift the wings in display, but their alternating wing waving, which they also show before take off, is unique. That they often balance with their outstretched wings during walking is probably an autapomorphy of darters, necessitated by their being plumper than the other Sulae. The Sulae were traditionally included in the Pelecaniformes, then a paraphyletic group of "higher waterbirds". The supposed traits uniting them, like all webbed toes and a bare gular sac, are now known to be convergent, and pelicans are apparently closer relatives of storks than of the Sulae. Hence, the Sulae and the frigatebirds – and some prehistoric relatives – are increasingly separated as the Suliformes, which is sometimes dubbed "Phalacrocoraciformes".

There are four living species of darters recognized, all in the genus Anhinga, although the Old World ones were often lumped together as subspecies of A. melanogaster. They may form a superspecies with regard to the more distinct anhinga:

Extinct "darters" from Mauritius and Australia known only from bones were described as Anhinga nana ("Mauritian darter") and Anhinga parva. But these are actually misidentified bones of the long tailed cormorant (Microcarbo/Phalacrocorax africanus) and the little pied cormorant (M./P. melanoleucos), respectively. In the former case, however, the remains are larger than those of the geographically closest extant population of long tailed cormorants on Madagascar: they thus might belong to an extinct subspecies (Mauritian cormorant), which would have to be called Microcarbo africanus nanus (or Phalacrocorax a. nanus) – quite ironically, as the Latin term nanus means dwarf. The Late Pleistocene Anhinga laticeps is not specifically distinct from the Australasian darter; it might have been a large paleosubspecies of the last ice age.

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