Austral storm petrel

Austral storm petrels, or southern storm petrels, belong to the seabird family Oceanitidae, which is part of the order Procellariiformes. They are the smallest seabirds, feeding by hovering and picking planktonic crustaceans and small fish from the water's surface. Their flight is fluttering and sometimes resembles that of a bat. They were once grouped with the Hydrobatidae as a single storm petrel family, but genetic analysis showed they are only distantly related, so the groups were split.

These birds have a cosmopolitan distribution across all oceans, though only Wilson's storm petrel and the white-faced storm petrel occur in the Northern Hemisphere. Almost all species are strictly pelagic, coming to land only to breed. Little is known about their behavior and distribution at sea, as they are difficult to find and identify. They nest in colonies, showing strong philopatry to their natal sites. Most nest in crevices or burrows, and all but one species visit their colonies only at night. Pairs form long-term monogamous bonds and share incubation and chick-feeding duties. Nesting is highly protracted, with incubation lasting up to 50 days and fledging taking another 70 days.

The family includes ten species in five genera. Several species are threatened by human activities. The New Zealand storm petrel was thought extinct until rediscovered in 2003. The main threats are introduced mammals, especially rats and feral cats, in breeding colonies; many storm petrels nest on isolated, mammal-free offshore islands and cannot cope with such predators.

The family Oceanitidae was introduced in 1881 by English zoologist William Alexander Forbes. Two subfamilies were traditionally recognized: Oceanitinae (austral storm petrels), mostly in southern waters with ten species in five genera, and Hydrobatinae (northern storm petrels), formerly in the genera Hydrobates and Oceanodroma and largely restricted to the Northern Hemisphere. Cytochrome b DNA analysis showed the family was paraphyletic, so they are now treated as distinct families. This study also found austral storm petrels are basal within Procellariiformes, with Oceanitidae diverging first and Hydrobatidae splitting later. Few fossils exist, the earliest from the Upper Miocene.

Austral storm petrels are the smallest seabirds, ranging from 15–26 cm in length. They have short wings, square tails, elongated skulls, and long legs. Their legs are proportionally longer than those of other Procellariiformes but are weak, unable to support the bird’s weight for more than a few steps. Plumage is dark with white underparts, except in Wilson's storm petrel. Onley and Scofield (2007) note that much published information is incorrect, and many photographs in major seabird references are misidentified; they also consider that some national bird lists include species accepted on inadequate evidence.

The ten species are: (list follows from source, but no new facts added).

Austral storm petrels typically breed in the Southern Hemisphere, unlike northern storm petrels. Several species migrate after breeding. Wilson's storm petrel is the most widely traveled, crossing the equator after breeding in Antarctica and subantarctic islands to reach the north Pacific and Atlantic. Others, like the grey-backed storm petrel, are essentially sedentary and do not migrate.

Storm petrels use various flight techniques. Most feed by surface pattering, holding and moving their feet on the water while hovering or using the wind to stay in place. This method is most common among austral storm petrels. The white-faced storm petrel has a unique variation: holding its wings motionless and angled into the wind, it pushes off the water in bounding jumps. They also use dynamic soaring and slope soaring, though the first is less common in this family; slope soaring, where the bird turns into the wind to gain height and then glides back down, is favored.

The diet of many species is poorly known due to research difficulties, but the family is thought to focus on crustaceans. Small fish and mollusks are also taken. Some species are more specialized; for example, the grey-backed storm petrel feeds mainly on goose barnacle larvae. Almost all forage in the pelagic zone, except Elliot's storm petrel, which feeds coastally in the Galapagos Islands. Though storm petrels swim well and form rafts on the water, they do not feed there; instead, they feed on the wing, hovering above or "walking" on the surface.