Shearwaters are medium-sized long-winged seabirds in the petrel family. They have a global marine distribution, but are most common in temperate and cold waters, and are pelagic outside the breeding season.
Description
These tubenose birds fly with stiff wings and use a "shearing" flight technique to move across wave fronts with the minimum of active flight. This technique gives the group its English name. Some small species, like the Manx shearwater are cruciformin flight, with their long wings held directly out from their bodies.
Behaviour
Movements
Many shearwaters are long-distance migrants, perhaps most spectacularly sooty shearwaters, which cover distances in excess of from their breeding colony on the Falkland Islands to as far as 70° north latitude in the North Atlantic Ocean off northern Norway. One study found Sooty shearwaters migrating nearly a year, which would give them the longest animal migration ever recorded electronically. Short-tailed shearwaters perform an even longer "figure of eight" loop migration in the Pacific Ocean from Tasmania to as far north as the Arctic Ocean off northwest Alaska. They are long-lived. A Manx shearwater breeding on Copeland Island, Northern Ireland, was the oldest known wild bird in the world: ringed as an adult in July 1953, it was retrapped in July 2003, at least 55 years old. Manx shearwaters migrate over to South America in winter, using waters off southern Brazil and Argentina, so this bird had covered a minimum of on migration alone.
Breeding
Shearwaters come to islands and coastal cliffs only to breed. They are nocturnal at the colonial breeding sites, preferring moonless nights to minimise predation. They nest in burrows and often give eerie contact calls on their night-time visits. They lay a single white egg. The chicks of some species, notably short-tailed and sooty shearwaters, are subject to harvesting from their nest burrows for food, a practice known as muttonbirding, in Australia and New Zealand.
Feeding
They feed on fish, squid, and similar oceanic food. Some will follow fishing boats to take scraps, commonly the sooty shearwater; these species also commonly follow whales to feed on fish disturbed by them. Their primary feeding technique is diving, with some species diving to depths of.
Taxonomy
There are about 30 species: a few larger ones in the genera Calonectris and Ardenna and many smaller ones in Puffinus. The Procellaria and Bulweria petrels were believed to belong to this group, but are only distantly related based on more recent studies, while the Pseudobulweria and Lugensa "petrels" are more closely related. The genus Puffinus can be divided into a group of small species close to Calonectris and a few larger ones more distantly related to both.
