petrel

Like all petrels, the Madeiran fork-tailed petrel has globular salt glands close to the eyes. About 100 species of petrels are known, most of which range over the cold southern seas. They are highly social birds, nesting in large colonies and feeding together in large, floating ‘rafts’.

Any of various families of seabirds in the order Procellariiforme, including the worldwide storm petrels (family Hydrobatidae), which include the smallest seabirds (some only 13 cm/5 in long), and the diving petrels (family Pelecanoididae) of the southern hemisphere. All have a hooked bill, rudimentary hind toes, tubular nostrils, and feed by diving underwater. They include fulmars and shearwaters.

Like other ground-nesting or burrow-nesting seabirds, petrels are vulnerable to predators such as rats that take eggs and nestlings. Several island species are in danger of extinction, including the Bermuda petrel Pterodroma cahow and the Freira petrel of Madeira P. madeira.

It is feared that 26 species are facing extinction, owing to habitat degradation, disturbance of breeding sites, and especially longline fishing, which kills up to 1,000 seabirds daily.

Species Storm petrels Hydrobates pelagicus are smoky brown with a broad band of white above the tail. Marine crustaceans constitute the natural food, but they also follow ships collecting scraps. Storm petrels are able to run lightly over the surface of the water with the aid of their wings. Wilson's storm petrel Oceanites oceanicus breeds in the southern hemisphere and migrates to the North Atlantic in winter. Seldom coming to land except to breed, Wilson's storm petrels lay a single egg in holes among the rocks. They are 18 cm/7 in long and sooty black with a white rump band.

The largest petrel, the Southern giant petrel Macronectes giganteus, is up to 1 m/3.3 ft long, with a wingspan of 2 m/6.6 ft. It is a scavenger with a powerful hooked beak, unusual among petrels in that it walks well on land. A forceful and powerful bird with behaviour resembling a vulture, it feeds on whatever it can find, including smaller burrowing petrels, unattended penguin chicks, and carrion such as dead seals. As a defence mechanism it spits oil at its attacker.

White-chinned petrels Procellaria aequinoctialis, known also as shoemakers from their courtship call, are among the first birds to return to breed on sub-Antarctic islands as winter retreats in September and October. They lay a single egg in an underground burrow. The snow petrel Pagodroma nivea with pure white body and black eyes and beak, is exceptional as the only flying bird to breed in the Antarctic interior, as far as 150 km from the coast. It nests in outcrops of rock in the ice.

In March 2001, an agreement to protect petrels and albatrosses was sanctioned by 12 nations.