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Leach's Storm Petrel | Hydrobates leucorhous
Vaal stormvogeltje | Paíño Boreal
Leach's Storm Petrel is a fairly large, long-winged storm petrel that breeds on northern ocean islands and winters in the tropical and southern Atlantic. It rarely follows ships and in southern Africa is mainly a bird of deep water beyond the shelf, where its erratic, tern-like flight gives it away.
Voice
Silent at sea. In the breeding colony at night a fast, rhythmic, stuttering chatter ending in a trill, and from the burrows a long, purring churr.
Recording: Doug Hynes — CC BY-SA 4.0 · converted to mono · xeno-canto
Identification
About 20 cm, dark grey-brown with a pale, broad bar across the upperwing coverts that reaches the leading edge of the wing. The white rump is narrow, often V-shaped and divided in the centre by a grey line; the sides of the undertail are dark. The wings are long, pointed and distinctly angled at the carpal, the tail is forked, though this is not always visible in flight. The feet do not reach beyond the tail. The sexes are alike. The flight is erratic and bounding, with deep wingbeats, sudden changes of direction and short glides, like that of a small tern.
Confusion species
Band-Rumped Storm Petrel (Hydrobates castro) has a cleaner white, undivided rump that wraps slightly onto the sides of the undertail, a less forked tail, a fainter wing bar and a flatter flight with more gliding. Wilson's Storm Petrel (Oceanites oceanicus) is smaller, with shorter, rounder wings, a square tail, a broad white rump and feet projecting beyond the tail. European Storm Petrel (Hydrobates pelagicus) is much smaller, with a white underwing stripe and a fluttering flight.
Habitat
Deep, open ocean water beyond the continental shelf, often over the shelf slope and in warmer water than Wilson's Storm Petrel. Feeds singly or in loose groups on zooplankton, small squid and fish larvae, picked from the surface in flight. Breeds in burrows on wooded or grassy islands.
Where the bird is most at home, classified by the vegetation units of southern Africa.
Range and movements
At sea off the west coast of the region, from Angola along Namibia to the Western Cape, usually far offshore; scarcer around the Cape of Good Hope and rare in the Mozambique Channel. After severe storms birds sometimes appear inshore or even inland. Breeds in the North Atlantic, from Newfoundland and Iceland to Scotland and Norway, and in the North Pacific; winters in the tropical and southern Atlantic.
How and when to look
The best chance is on a pelagic trip beyond the shelf edge in the austral summer. Leach's Storm Petrel seldom joins the wake but passes singly or in small numbers in a swooping flight; watch for the long, angled wings and the pale wing bar. After westerly gales it pays to scan Table Bay and the coast near Walvis Bay.
Conservation status
Vulnerable. The species is still numerous, but the large colonies in the western North Atlantic, especially on Newfoundland, have declined steeply in recent decades. Causes include predation by gulls and mammals in the colonies, attraction to lights on oil platforms and ships, and changes in food supply at sea.
Scientific name
Hydrobates leucorhous | (Vieillot, 1818) (GBIF: Oceanodroma leucorhoa)
Vieillot described the species in 1818 as Procellaria leucorhoa; because it was later moved to another genus, the author and year stand in brackets. The genus Hydrobates was introduced in 1822 by Boie. Hydrobates is Greek, from hudro- 'water' and batēs 'walker': 'water walker'. leucorhous is Greek, from leukos 'white' and orrhos 'rump', after the white rump band. The specimen the first description was based on came from the coast of Picardy.