Gadfly petrel of medium size. Dark gray upperparts and white below with a diagonal black bar from the edge of the wing to the black base of the underwing. Has a black bill, a dark eye-patch, and pink legs and feet. Breeds only on the Chatham Islands, but can forage up 3000 km offshore. Migrates to deep waters off the South American coast. Distinguished from Black-winged Petrel by the reduced black bar on the underwing; Mottled Petrel is similar but larger, with a dark belly, lacking the diagonal bar on the wing.