A medium-sized shearwater with uniformly dark brown plumage and no contrasting markings. Flies more steadily than most shearwaters and usually flies low over the water. Large numbers nest on most of the Northwestern Hawaiian Islands. A few pairs nest on Moku Manu Islet off the eastern coast of Oahu. Often seen from boats in the Northwestern Hawaiian Islands, but rarely on the main islands and rarely from shore. The voice, usually heard only at breeding colonies, is a low moan.