Wilson's Storm Petrel Oceanites oceanicus
Wilson's storm-petrel (Oceanites oceanicus) is a small storm-petrel with short, rounded wings and long legs projecting beyond the tail in flight. They are about 18cm in length with a wing span of approximately 40cm Their upperparts are mostly sooty-brown except for a conspicuous white rump and a pale brown band showing across the greater wing-coverts. Their underside is mainly sooty-brown.
There are two extant subspecies, and another, O.o. maorianus is now believed to be extinct. O.o. maorianus is known only from three individuals collected on New Zealands sub-Antarctic islands.
Wilson's storm-petrel are numerous and wide ranging. They migrate from their Antarctic breeding grounds to north of the Equator in the Atlantic, Indian and Pacific Oceans. Few birds migrating north into the eastern Pacific Ocean. Their range overlaps with many other storm-petrel species. They breed on the Antarctic continent, South Georgia, Kerguelen, Falklands, Tierra del Fuego islands off Cape Horn; perhaps also at Peter, Bouvet, Heard, the Balleny Islands and islands off Graham Land. Non breeders may remain north throughout the year. Wilson's storm-petrel return to their colonies in November/December and eggs are laid in mid-December (but about one month later at Heard and IlesKerguelen). Both parents share the 39-48 day incubation period, taking alternative shifts of about 48 hours. Once the chicks hatch they are fed irregulary by both parents for up to 52 days. Fledging and dispersion begins in April/May At nesting sites Wilson's storm-petrel are killed by skuas. Starvation, due to the blocking of the burrow by hard snow, is a cause of chick mortality..
Wilson's storm petrel are gregarious at sea with flocks reaching several thousands at staging points during migration. They feed by running along the surface of the water with wings outstretched and bill (or their entire head) submerged in the water to scoop in their food, taking minutiae from the surface. They feed on crustacea (amphipods and Euphausia), cephalopods (squid), fish, offal, etc. The birds readily follow ships and attend trawlers, attracted by the left-overs, and cetaceans (whales, dolphins etc).
Above text adapted from that written by Eric Woehler, AAD, and Maria Clippingdale, AADC.
Purple Martin is vaguely similar but lacks the white rump patch and doesn't usually occupy the same habitat. Shearwaters are much larger. Other storm petrels are very similar. Black, Ashy, and Least storm-petrels lack the white rump. Wedge-rumped storm-petrel is smaller with a larger rump patch. Band-rumped and Leach's storm petrels are larger with different flight styles and their feet don't protrude beyond the end of their tails. Leach's has a forked tail and a divided or absent rump patch. Band-rumped has a thinner rump patch.
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