Shearwater


Shearwaters are medium-sized long-winged seabirds in the petrel family Procellariidae. 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 cruciform in 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 colonies on the Falkland Islands to as far as 70° north latitude in the North Atlantic Ocean off northern Norway, and around New Zealand to as far as 60° north latitude in the North Pacific Ocean off Alaska. A 2006 study found individual tagged sooty shearwaters from New Zealand migrating a year, which gave them the then longest known 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 also 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.
Following the tracks of the migratory Yelkouan shearwater has revealed that this species never flies overland, even if it means flying an extra 1,000 km. For instance, during their seasonal migration towards the Black Sea they would circumvent the entire Peloponnese instead of crossing over the 6 km Isthmus of Corinth.

Breeding

Shearwaters come to islands and coastal cliffs only to breed. They are nocturnal at the colonial breeding sites, preferring moonless nights to minimize 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

Shearwaters 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. Shearwaters defecate more often than other seabirds, typically between once every four to ten minutes. They excrete five percent of their body mass every hour, generally done while flying, rather than while resting on water.

Taxonomy

There are about 30 species: a few larger ones in the genera Calonectris and Ardenna and many smaller ones in Puffinus. Recent genomic studies show that Shearwaters form a clade with Procellaria, Bulweria and Pseudobulweria. This arrangement contrasts with earlier conceptions based on mitochondrial DNA sequencing.

List of species

The group contains 3 genera with 32 species.
There are two extinct species that have been described from fossils.
Phylogeny of the shearwaters based on a study by Joan Ferrer Obiol and collaborators published in 2022. Only 14 of the 21 recognised species in the genus Puffinus were included.