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Darter
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The darters or snake-birds are birds in the family Anhingidae. There are four living species, one of which is near-threatened. The darters are frequently referred to as snake-birds because of their long thin neck, which gives a snake-like appearance when they swim with their bodies submerged.
The darters are large birds with sexually dimorphic plumage. The males have black and dark brown plumage, an erectile crest on the nape and a larger bill than the female.
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The darters or snake-birds are birds in the family Anhingidae. There are four living species, one of which is near-threatened. The darters are frequently referred to as snake-birds because of their long thin neck, which gives a snake-like appearance when they swim with their bodies submerged.
The darters are large birds with sexually dimorphic plumage. The males have black and dark brown plumage, an erectile crest on the nape and a larger bill than the female. The females have a much paler plumage especially on the neck and underparts. Both have grey stippling on long scapulars and upper wing coverts. The sharply pointed bill has serrated edges. The darters have completely webbed feet, and their legs are short and set far back on the body. Their plumage is somewhat permeable, like that of cormorants, and they spread their wings to dry after diving. Vocalizations include a clicking or rattling when flying or perching. During breeding adults sometimes have caw or hissing calls.
Range
Darters are circum-equatorial, tropical or subtropical. They inhabit either fresh or brackish water and can be found in lakes, rivers, marshes, swamps, estuaries, bays, lagoons and mangrove swamps. They tend to gather in flocks sometimes up to about 100 birds but are highly territorial when breeding. Most are sedentary and do not migrate, however the populations at extreme distributions may migrate. The Oriental Darter is near-threatened species. Habitat destruction along with other human interferences is among the main reasons for a declining population.
Food and feeding
Darters feed mainly on fish. They use their sharply pointed bill to spear their prey when they dive; this is how they get the name darter. Their ventral keel is present on the 5-7 vertebrae which allows for muscles to attach so that they are able to project their bill forward like a spear. They also eat amphibians such as frogs and newts, reptiles such as snakes and turtles and invertebrates such as insects, shrimp and mollusks. These birds use their feet to move underwater and quietly stalk and ambush their prey. They then stab the prey, such as a fish, and bring them to the surface where they toss it into the air and catch and swallow it.
Breeding
The darters are monogamous and pair bond during the breeding season. There are many different types of displays used for mating including male displays to attract the female, greeting displays between the male and female and pair bonding displays between the pairs. Also during breeding, their small gular sac changes from pink or yellow to black and the bare facial skin turns to turquoise from a yellow or yellow-green color. They usually breed in colonies.
Breeding can be seasonal or year round and varies by geographic range. The nests are made of twigs and are built in trees or reeds, often near water. The clutch size is two to six eggs (usually about 4) of a pale green color and the eggs are incubated for 25 to 30 days. The eggs hatch asynchronously. Bi-parental care is given and the young are considered altricial. They reach sexual maturity by about 2 years. These birds generally live to around 9 years.
Systematics and evolution
This family is very closely related to the other families in the Pelecaniformes suborder Sulae, i.e. the cormorants and shags and the gannets and boobies. Cormorants and anhingas are extremely similar as regards their body and leg skeletons, showing that they are closely related. In fact, several anhinga fossils were initially believed to be cormorants or shags (see below for examples).
There are four living species of darters recognized, all in the genus Anhinga, although the Old World ones are often lumped together as subspecies of A. melanogaster:
Extinct "species" from Mauritius and Australia known only from bones were described as Anhinga nana ("Mauritian Darter") and Anhinga parva, but they were misidentifications of bones of the Long-tailed Cormorant and the Little Pied Cormorant, respectively. In the former case, however, they might belong to an extinct subspecies which would have to be called Phalacrocorax africanus nanus (Mauritian Cormorant) - quite ironically, as nanus means "dwarf" and the remains are larger than those of the geographically closest population of the Long-tailed Cormorant.
The darters are known since the Early Miocene. The diversity was highest in the Americas; a number of prehistoric species and genera known only from fossils have been described. The aptly named Macranhinga, Meganhinga and Giganhinga represent very large and at least partly flightless forms:
- Meganhinga (Early Miocene of Chile)
- Macranhinga (Middle/Late Miocene -? Early Pliocene of SC South America)
- Giganhinga (Late Pliocene/Early Pleistocene of Uruguay)
- Anhingidae gen. et sp. indet. (Middle/Late Miocene of Paraná, Argentina)
Prehistoric members of Anhinga are:
- Anhinga subvolans (Early Miocene of Thomas Farm, USA) - formerly in Phalacrocorax
- Anhinga cf. grandis (Middle Miocene of Colombia -? Late Pliocene of SC South America)
- Anhinga sp. (Sajóvölgyi Middle Miocene of Mátraszőlős, Hungary)
- Anhinga fraileyi (Late Miocene -? Early Pliocene of S South America)
- Anhinga minuta (Solimőes Late Miocene/Early Pliocene of SC South America)
- Anhinga pannonica (Late Miocene/Early Pliocene of Tatarus-Brusturi, Hungary ?and Tunisia, East Africa, Pakistan and Thailand - ?Sahabi Early Pliocene of Libya)
- Anhinga grandis (Late Miocene - Kimball Late Pliocene of USA)
- Anhinga malagurala (Allingham Early Pliocene of Charters Towers, Australia)
- Anhinga sp. (Early Pliocene of Bone Valley, USA)
- Anhinga hadarensis (Late Pliocene/Early Pleistocene of E Africa)
- Anhinga sp. (Early Pleistocene of Coleman, USA) - may be same as Anhinga sp. "Bone Valley"
The Pleistocene Anhinga laticeps is a misidentified Australian Darter; it might have been a paleosubspecies of the last ice age.
Footnotes
External links
- on the Internet Bird Collection
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