A generic Storm-petrel. Believed to be most closely related to Elliot's Storm-petrel from the Galapagos and Humbolt Current. Two races known, O. o. oceanicus breeding primarily on subantarctic islands and O. o. exasperatus breeding close to or on the Antarctic Continent.

Figure 1. Wilson's Storm-petrel in the warm blue waters of the Gulf Stream off North Carolina, USA. Notice the yellow webs to the feet. Photographed in May by Angus Wilson©
 

Identification

A small storm-petrel, slightly larger than European Storm-petrel. Feet project beyond tail in direct flight. Flight style reminiscent of swallows, short wing beats interspersed with glides. When pattering (i.e. feeding) hops over the water with wings held in a sharp V. Legs hang below the body and are used to push off the surface. Doesn't give the bat-like impression of European Storm-petrel. At close range, distinctive yellow webs to feet are visible. Molt cycle follows a southern hemisphere timetable. Adults are most worn during the northern spring and early summer while the juveniles become very worn in late summer (August), appearing much browner with ragged looking wings, often missing primaries. Generally silent away from nesting grounds, but sometimes emit rapid squeaks or chattering.

When handled, Wilson's Storm-petrels eject a clear oil which is so fine that it can penetrate clothing. The oil's odor is described as not terribly objectionable but somewhat musty and hard to get rid of.
 

Where and When

The nominate race (oceanicus) breeds on islands off Tierra del Fuego, The Falklands, South Georgia, Crozets and other island groups in the southern ocean. The race exasperatus is an abundant breeder on the islands of the Scotia Arc, South Shetland Is., South Sandwich Is., S. Orkney Is., Elephant Is. and on the Antarctic Continent itself. Nests are built in rocky rubble.

Outside of the breeding season (i.e. the northern summer), disperses widely in the northern hemisphere, being especially abundant in the Gulf Stream off North America and in the Arabian Sea. Can occur close to shore (at least in eastern North America), even feeding along the surf line.
 

Behaviour

An agile bird, well-known for bouncing along patting the water surface with both feet. Despite its small size, a powerful flier being able to maintain its position in winds reaching 40 knots. Although not generally considered a diver, Murphy observed Wilson's Storm-petrels diving to several body lengths to retrieve sinking food items. Easily attracted to boats using fish scraps or oils. Sometimes forms tight rafts (up to 30 birds) while roosting at sea, sometimes large flocks assemble prior to migration.
 

Literature

Orgeira, J. L. (1994) Registros del Petrel de Wilson (Oceanites oceanicus) en el Mar de Weddell, Antartida. Cont. Cient. Inst. Antartico Argentino 436: 1-5