The Phalacrocoracidae family of birds is represented by 38 species of cormorants and shags. Several different classifications of the family have been proposed recently, but in the one most commonly used, all but three species are placed in a single genus Phalacrocorax, the exceptions being the Galapagos' Flightless Cormorant, the Kerguelen Shag and the Imperial Shag.
There is no consistent distinction between cormorants and shags. The names "cormorant" and "shag" were originally the common names of the two species of the family found in Great Britain, Phalacrocorax carbo (now referred to by ornithologists as the Great Cormorant) and P. aristotelis (the Common Shag). "Shag" refers to the bird's crest, which the British forms of the Great Cormorant lack. As other species were discovered by English-speaking sailors and explorers elsewhere in the world, some were called cormorants and some shags, depending on whether they had crests or not. Sometimes the same species is called a cormorant in one part of the world and a shag in another, e.g. the Great Cormorant is called the Black Shag in New Zealand (the birds found in Australasia have a crest that is absent in European members of the species). Some modern classifications of the family have divided it into two genera and have tried to attach the name "Cormorant" to one and "Shag" to the other, but this flies in the face of common usage and has not been widely adopted.
The scientific genus name is latinized Ancient Greek, from phalakros (bald) and korax (raven). "Cormorant" is a contraction derived from Latin corvus marinus, "sea raven". Indeed, "sea raven" or analogous terms were the usual terms for cormorants in Germanic languages until after the Middle Ages, and the erroneous belief that these birds were related to ravens lasted at least to the 16th century:
"...le bec semblable à celuy d'un cormaran, ou autre corbeau." (...the beak similar to that of a cormorant or other corvids."; Thevet, 1558).
Cormorants and shags are medium-to-large seabirds. The majority, including all Northern Hemisphere species, have mainly dark plumage, but some Southern Hemisphere species are black and white, and a few (e.g. the Spotted Shag of New Zealand) are quite colourful. Many species have areas of colored skin on the face (the lores and the gular skin) which can be bright blue, orange, red or yellow, typically becoming more brightly colored in the breeding season. The bill is long, thin, and sharply hooked. Their feet are four-toed and webbed, a distinguishing feature among the Pelecaniformes order.
They are coastal rather than oceanic birds, and some have colonised inland waters. They range around the world, except for the central Pacific islands.
All are fish-eaters, dining on small eels, fish, and even water snakes. They dive from the surface, though many species make a characteristic half-jump as they dive, presumably to give themselves a more streamlined entry into the water. Under water they propel themselves with their feet. Some cormorant species have been found, using depth gauges, to dive to depths of as much as 45 metres.
After fishing, cormorants go ashore, and are frequently seen holding their wings out in the sun; it is assumed that this is to dry them. Unusually for a water bird, their feathers are not waterproofed. This may help them dive quickly, since their feathers do not retain air bubbles.
Cormorants are colonial nesters, using trees, rocky islets, or cliffs. The eggs are a chalky-blue colour. There is usually one brood a year. The young are fed through regurgitation. They typically have deep, ungainly bills which make it obvious that they are related to pelicans.
Humans have historically exploited cormorants' fishing skills, in China, Japan, and Macedonia, where they have been trained by fishermen. In Japan, traditional cormorant fishing can be seen in Gifu City, in Gifu Prefecture, where it has continued uninterrupted for 1300 years, or in the city of Inuyama, in Aichi Prefecture. In Guilin, China, cormorant birds are famous for fishing on the shallow Lijiang River. A snare is tied near the base of the bird's throat, a snare that allows the bird only to swallow small fish. When the bird captures and tries to swallow a large fish, the fish gets stuck in the bird's throat. When the bird returns to the fisherman's raft, the fisherman helps the bird to remove the fish from its throat. The method is not as common today, since more efficient methods of catching fish have been developed.