Hydrobatidae – Northern Storm Petrels

The Hydrobatidae (Northern Storm Petrels) are, along with other seabirds –  Diomedeidae (Albatrosses), Oceanitidae, Austral 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 northern hemisphere.

Two subfamilies were traditionally recognised. The Oceanitinae that are mostly found in southern waters (though the Wilson’s storm petrel regularly migrates into the northern hemisphere); there are seven species in five genera. The Hydrobatinae are the two genera Hydrobates and Oceanodroma. They are largely restricted to the northern hemisphere, although a few can visit or breed a short distance beyond the equator. Cytochrome b DNA sequence analysis suggests that the family is paraphyletic and so they are now more accurately treated as distinct families.

European Storm Petrels Hydrobates pelagicus – ©Richard Crossley CC BY-SA 3.0 via Wikimedia Commons

These smallest of seabirds feed on planktonic crustaceans and small fish picked from the surface, typically while hovering. Their flight is fluttering and sometimes bat-like. They are strictly pelagic, coming to land only when breeding. In the case of most species, little is known of their behaviour and distribution at sea, where they can be hard to find and harder to identify. They are colonial nesters, displaying strong philopatry to their natal colonies and nesting sites. 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 seabird, nesting is highly protracted with incubation taking up to 50 days and fledging another 70 days after that.

Markham’s Storm Petrel Hydrobates markhami – ©thibaudaronson CC BY-SA 4.0 via Wikimedia Commons

The diet of many storm petrel species is poorly known owing to difficulties in researching; overall the family is thought to concentrate on crustaceans. Small fish, oil droplets and molluscs are also taken by many species. Some species are known to be rather more specialised; the Grey-backed Storm Petrel, for example, is known to concentrate on the larvae of Goose Barnacles.

Almost all species forage in the pelagic zone. Although storm petrels are capable of swimming well and often form rafts on the water’s surface, they do not feed on the water. Instead feeding usually takes place on the wing, with birds hovering above or ‘walking’ on the surface (see morphology) and snatching small morsels. Rarely prey is obtained by making shallow dives under the surface.