Phalacrocoracidae – Cormorants & Shags

The Phalacrocoracidae is a family of some 41 species of aquatic birds commonly known as cormorants or shags. Several different classifications of the family have been proposed recently, and the number of genera is disputed. There is no consistent distinction between cormorants and shags as these appellations have been assigned to different species seemingly randomly.

They are medium-to-large seabirds. They range in size from the Pygmy Cormorant Phalacrocorax pygmaeus, at as little as 45cm and 340g, to the Flightless Cormorant Phalacrocorax harrisi, at a maximum size 100cm and 5kg. The recently extinct Spectacled Cormorant Phalacrocorax perspicillatus was rather larger, at an average size of 6.3kg. The majority, including nearly 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 coloured skin on the face (the lores and the gular skin) which can be bright blue, orange, red or yellow, typically becoming more brightly coloured in the breeding season. The bill is long, thin, and sharply hooked. Their feet have webbing between all four toes, as in their relatives.

They are coastal rather than oceanic birds, and some have colonised inland waters – indeed, the original ancestor of cormorants seems to have been a fresh-water bird, judging from the habitat of the most ancient lineage. They range around the world, except for the central Pacific islands.

All are fish-eaters, taking small eels, other 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, though some also propel themselves with their wings. Some cormorant species have been found 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. All cormorants have preen gland secretions that are used ostensibly to keep the feathers waterproof. Some sources state that cormorants have waterproof feathers while others say that they have water permeable feathers. Still others suggests that the outer plumage absorbs water but does not permit it to penetrate the layer of air next to the skin. The wing drying action is seen even in the flightless cormorant but commonly in the Antarctic Shag and Red-legged Cormorant. Alternate functions suggested for the spread-wing posture include that it aids thermoregulation, digestion, balances the bird or indicates presence of fish. A detailed study of the great cormorant concludes that it is, without doubt, to dry the plumage.

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, showing a greater resemblance to those of the pelicans, to which they are related, than is obvious in the adults.