Medium-sized, long-tailed graceful seabird, breeding on outer islands of Japan. Grayish above, whitish below, with blackish “M” pattern in upperwing, blackish cap or cowl, and bold black bars in white underwing that form a unique pattern (with extensive black in the primaries). Black-winged Petrel has much narrower black bars in underwing and blackish trailing edge to upperwing. Plumage may also resemble much larger Hawaiian Petrel, but Hawaiian has darker crown and narrower black bars in underwing.