Hydrobatidae

Small seabirds, storm petrels are well adapted for flying and swimming. When foraging, they have a habit of fluttering just above the sea, with their feet dangling or pattering on the surface, so that they seem to be walking on the water. The life history of many species is poorly known; for example the breeding grounds of Ringed Storm Petrel (Oceanodroma hornbyi) are still unknown, and those of Markham's Storm Petrel (O. markhami) were discovered only in 1987.

Additional information

All species have a hooked bill and tubed nostrils on the culmen ridge. Well developed salt glands filter excess salt from food and water, and secrete it through this 'tube-nose'. The sense of smell is extraordinary and is used to locate food al long distances. The birds have webbed feet and are good swimmers. However, they cannot stand for more than a few moments or walk more than a few steps because their legs, positioned right at the rear of the body, cannot bear the body weight.

The birds are gregarious at colonies, but at sea they are solitary or occur in small flocks or feeding aggregations, usually around concentrations of food resources. They rest on the water singly or in groups ('rafts') between feeding bouts, which can occur day or night. Agile and active fliers, their flight may be fluttering or strong and direct, depending on species and weather conditions. Most 'walk' or patter on the surface as they forage, and either pick food from the surface or grab it in shallow dives. Both adults and chicks eject stomach oil from the mouth and nostrils as a form of defense. The birds' difficulty in walking makes them vulnerable on land, with the exception of Wedge-rumped Storm Petrel (O. tethys) at the Galapagos Islands, they come ashore only in twilight or darkness.

Birds arrive at the colony well in advance of breeding, to establish territory, engage in displays, and reunite with or obtain a mate. They are monogamous, probably pairing for life. They nest in burrows dug by themselves, other seabirds, or animals, and lay one proportionately large egg. Young birds return to the colony as 'spectators' at 2-4 years old, but most probably do not breed until 3-5 years.

Taxonomy

Number of genera: 7

Number of species: 21

A list of all species can be found here.

They are classified in two subfamilies, distinguished by the relative proportions of the wings and legs: Oceanitinae, with shorter, more rounded wings, shorter tail, and long legs, and Hydrobatinae, with longer, pointed wings; long (often forked tail), and shorter legs.