A large, long-winged petrel that appears mostly dark above and white below. The forehead is white and the underwings have a broad black diagonal bar. The flight is fast with high arcing turns. Nests in the mountains on several of the main Hawaiian Islands. At breeding colonies it is usually active only at night. Regularly observed offshore from boats and can be seen from shore at dusk in some areas. Calls include a long, low “uuuuu-wah-uuu,” and various sharp yaps and barks.