Uncommon resident of Galapagos. Population estimated at 15,000 pairs in 15 colonies. Nests in burrows or crevices, breeding throughout the year, with two different populations nesting in the same areas at different times.
A medium-sized storm-petrel with relatively broad, blunt-tipped wings; moderately long, slightly forked tail; and a rather 'bull-necked' appearance. The legs do not protrude beyond tail in flight. Upper parts uniform dark brown with paler brown bar on upper wing. Narrow, but prominent, 'U'-shaped white rump extends to the lateral undertail-coverts; at close range may show dark feathers at rear of white rump. Under parts entirely dark.
Silent at sea but calls at night near the breeding colony: a squeaky "whikka-whikka.." rather like rubbing a wet finger on a glass.
Pelagic, feeding well offshore and rarely seen close to land. Flight action rather buoyant with rapid, shallow wing beats and low, shearing glides reminiscent of Audubon's Shearwater, with the wings held flat or slightly bowed. Progresses in a zigzag manner but occasionally becomes erratic, banking and 'jinking' and doubling back. Does not follow ships but sometimes attracted to lights at night. Visits colonies nocturnally.