The Phalacrocoracidae family of birds is represented by over thirty species of cormorants and shags. All but three are in the genus Phalacrocorax, the exceptions being the Galapagos Flightless Cormorant, the Kerguelen Shag and the Imperial Shag.
The names "cormorant" and "shag" were originally those of the two species of the family found in Great Britain, Phalacracorax carbo (the Great Cormorant) and P. aristotelis (the Common Shag). "Shag" refers to the bird's crest.
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).
Christopher Isherwood was obviously unaware of the distinction when he began a poem, "The common cormorant (or shag)/lays eggs inside a paper bag". His information about the bird's nesting habits shouldn't be relied on, either.
Cormorants and shags are medium-to-large seabirds, usually with mainly dark plumage and areas of coloured skin on the face which are bright blue, orange, red or yellow. The bill is long, thin, and sharply hooked. Their feet are four-toed and webbed, a distinguishing feature among the Pelecaniformes order.
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.
After fishing, cormorants go ashore to dry their wings by holding them out in the sun. 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.
Humans have historically exploited cormorants' fishing skills, especially in Japan, where they have been trained by fishermen. Traditional cormorant fishing can be watched in the city of Inuyama, in Aichi prefecture.
This group is related to other Pelecaniformes as below:
The Spectacled Cormorant Phalacrocorax perspicillatus is extinct.
For an alternative scientific classification, see Sibley-Ahlquist taxonomy.