Hydrobates pelagicus

The European storm petrel, British storm petrel, or just storm petrel (Hydrobates pelagicus) is a seabird in the northern storm petrel family, Hydrobatidae. It is the only member of the genus Hydrobates. The small, square-tailed bird is entirely black except for a broad, white rump and a white band on the under wings, and it has a fluttering, bat-like flight. The large majority of the population breeds on islands off the coasts of Europe, with the greatest numbers in the Faroe Islands, United Kingdom, Ireland, and Iceland. The Mediterranean population is a separate subspecies, but is inseparable at sea from its Atlantic relatives; its strongholds are Filfla Island (Malta), Sicily, and the Balearic Islands. The storm petrel nests in crevices and burrows, sometimes shared with other seabirds or rabbits, and lays a single white egg, usually on bare soil. The adults share the lengthy incubation and both feed the chick, which is not normally brooded after the first week. This bird is strongly migratory, spending the Northern Hemisphere winter mainly off the coasts of South Africa and Namibia, with some birds stopping in the seas adjoining West Africa, and a few remaining near their Mediterranean breeding islands. This petrel is strictly oceanic outside the breeding season. It feeds on small fish, squid, and zooplankton, while pattering on the sea's surface, and can find oily edible items by smell. The food is converted in the bird's stomach to an oily orange liquid, which is regurgitated when the chick is fed. Although usually silent at sea, the storm petrel has a chattering call given by both members of a pair in their courtship flight, and the male has a purring song given from the breeding chamber. The storm petrel cannot survive on islands where land mammals such as rats and cats have been introduced, and it suffers natural predation from gulls, skuas, owls, and falcons. Although the population may be declining slightly, this petrel is classified by the International Union for Conservation of Nature as being of least concern due to its high total numbers. Its presence in rough weather at sea has led to various mariners' superstitions, and by analogy, to its use as a symbol by revolutionary and anarchist groups. The storm petrels, Hydrobatidae, are one of the four major families of the Procellariiformes or 'tubenoses', an order of seabirds that also includes the albatrosses, the Procellariidae, and the diving petrels. The family is an ancient group of small species that is thought to have diverged early from the rest of the tubenoses; the supporting fossil record is poor, with specimens from California dating back only to the Late Miocene (11.6–5.3 million years ago). The Hydrobatidae are often divided into two subfamilies, the mainly Southern Hemisphere Oceanitinae and the northern Hydrobatinae; cytochrome b DNA sequence analysis suggests that these might be full families. The European storm petrel is the only member of the genus Hydrobates, the remainder of the Hydrobatinae being placed in Oceanodroma, although the least storm petrel is sometimes separated as the sole member of Halocyptena. The relationships within the Hydrobatinae are complex and uncertain, and all the members of the subfamily could be subsumed into an enlarged Hydrobates. The storm petrel was first described by Linnaeus in his Systema naturae in 1758 as Procellaria pelagica. It was moved to the genus Hydrobates by Friedrich Boie in 1822. 'Petrel', first recorded in 1602, is a corruption of pitteral, referring to the bird's pitter-pattering across the water. The suggestion that the word refers to St Peter walking on the waves is a later invention. Storm arises from seamen's association of this bird with bad weather. In English, the name of the species was written as 'stormy petrel' by some 19th-century authors. The scientific name derives from Ancient Greek; Hydrobates is from hudro, water, and bates, walker, and pelagicus is from pelagikos, of the sea. There are two recognised subspecies, the North Atlantic nominate subspecies, H. p. pelagicus (Linnaeus, 1758), and the Mediterranean H. p. melitensis (Schembri, 1843). Although there is some genetic support for classifying the southern form as a separate species, the morphology is not considered sufficiently different from that of the nominate subspecies to justify a split. The storm petrel is a small bird, 14–18 cm (5.5–7.1 in) in length with a 36–39 cm (14–15 in) wingspan. It weighs 20–38 g (0.71–1.34 oz), with an average of 28 g (0.99 oz). It is square-tailed and has all-black plumage except for a snow-white rump that extends to the sides of the tail base and a broad white band on the under wings. Juveniles in fresh plumage can also show a narrow white bar on the upper wing. The plumage becomes dark brown rather than black as it becomes worn. No obvious differences between the sexes are seen, although in the Mediterranean subspecies, at least, most captured birds can be sexed using a formula which involves multiplying the wing length by the length of the white rump band; females are slightly larger and have a longer white rump than males. The Mediterranean subspecies has longer wings and a heavier bill on average than the nominate form, but neither sex nor subspecies can be determined by observation at sea. Moult is prolonged in all tubenoses, since they must maintain an ability to fly. Northern populations start replacing their plumage after those further south, reflecting the later start to their breeding season. Birds in a Welsh colony commenced moulting in early August, while populations in northern Spain and the Balearics started in early July and mid-June, respectively. Breeding birds moult later than non-breeders.