Oceanitidae – Austral Storm Petrels

The Oceanitidae – Austral Storm Petrels – are, along with Diomedeidae (Albatrosses), Hydrobatidae (Northern Storm Petrels) and Procellariidae (Shearwaters, Petrels & Diving Petrels) part of the Procellariiformes order. They are found in all the world’s oceans but, are predominantly found in the southern hemisphere – only Wilson’s & White-faced Sorm Petrels are found in the northern hemisphere.

The family contains five genera, in which there are ten species. They were the second group of storm petrels to break off from the ancestral petrel stock, and for this reason, it was recently agreed that they constitute a separate family from the other Procellariiformes.  The New Zealand storm petrel was presumed extinct until recently rediscovered (2003) by birdwatchers.

They are some of the smallest of all the seabirds, ranging in size from 13–26 cm in length, with short wings, square tails, elongated skulls, and long legs. The legs of all storm petrels are proportionally longer than those of other Procellariiformes, but they are very weak and unable to support the bird’s weight for more than a few steps. They are notoriously difficult to identify at sea.

The plumage of all the Oceanitidae (with the exception of Wilson’s storm petrel) is dark with white underparts. It has been suggested (Onley and Scofield 2007) that much published information is incorrect, and that photographs, even in some of the major seabird books and websites, are frequently incorrectly ascribed as to species. It is also thought that several national bird lists include species which have been incorrectly identified or have been accepted on inadequate evidence.

Wilson’s Storm Petrel Oceanites oceanicus – ©Dubi Shapiro

This family use a variety of techniques to aid flight. Most species will occasionally feed by surface pattering, holding and moving their feet on the water’s surface while holding steady above the water, and this method of feeding flight is the method most commonly used by Austral Storm Petrels. The White-faced Storm Petrel possesses a unique variation on pattering, holding its wings motionless and at an angle into the wind, it pushes itself off the water’s surface in a succession of bounding jumps. Storm petrels also use dynamic soaring and slope soaring to travel over the ocean surface, although this method is used less by this family compared to the northern storm petrels. Slope soaring is favoured by the Oceanitidae, the storm petrel turns to the wind, gaining height, from where it can then glide back down to the sea.

They feed on planktonic crustaceans and small fish picked from the surface, typically while hovering. Their usual flight is fluttering and is sometimes described as like that of bats. Some species are known to be rather more specialised; for example, the Grey-backed Storm Petrel is known to concentrate on the larvae of goose barnacles. Like many types of seabirds, storm petrels associate with other species of seabird and marine mammal species to help obtain food. They may benefit from the actions of diving predators such as seals and penguins, which push prey up towards the surface while hunting, allowing the surface-feeding storm petrels to reach them.

Grey-backed Storm Petrel Garrodia nereis – ©JJ Harrison CC BY-SA 3.0 via Wikimedia Commons

They are almost all strictly pelagic, coming to land only when breeding (Elliot’s Storm Petrel is an exception feeding in the Galapagos Islands’ coastal waters). In the case of most petrel species, little is known of their behaviour and distribution at sea, where they can be hard to find. They are colonial nesters, displaying strong philopatry to their natal colonies and nesting sites. Some colonies are enormous with over threequarters of a million birds. Most species nest in crevices or burrows, and all but one species attend the breeding colonies nocturnally. Pairs form long-term monogamous bonds and share incubation and chick-feeding duties. Like many species of seabirds, nesting is highly protracted with incubation taking up to 50 days and fledging another 70 days after that.

Several species are threatened by human activities. The principal threats to storm petrels are introduced species, particularly mammals, in their breeding colonies; many storm petrels habitually nest on isolated mammal-free islands and are unable to cope with predators such as rats and feral cats.