Hydrobates leucorhous
Forked and fairly long tail. Clearly bigger than Storm Petrel, with more slender appearance and longer wings. Generally not as black, and shows brownish tone to plumage. The white rump patch is oval, has a weak grey center stripe, and does not reach as far down on the sides as in Storm Petrel. Light grey upper greater coverts form a wing-band. Underside of wings all dark. Flight pattern variable, with frequent changes in direction and speed. Sometimes glides like a shearwater but at other times shows surprisingly deep wing-beats. Does not patter surface, but will rest on water. Visits breeding ground only at night, and is usually only seen after storms.
Only calls at breeding ground. A series of accentuated cooing, interrupted by a squeaky "inbreath" and a loud, absurd, fanfare-like "kaaa-ka-ka-kaaa-ka".
Wikipedia: map (se also Xeno-canto below)
Birdlife ecology
