The Westland Petrel is a large, dark petrel of the South Pacific Ocean. It closely resembles White-chinned Petrel (Procellaria aequinoctialis) and Parkinson's Petrel (P. parkinsoni), both of which co-occur with Westland to some extent. Most individuals lack the white chin and entirely pale bill of White-chinned. Separation from Parkinson's is more difficult and is based largely on the larger size, relatively shorter wings, and thicker bill of Westland as well as differences between the two species in the timing of the molts. Westland breeds on the South Island of New Zealand, and disperses eastward to the central Pacific and Humboldt Current off Chile and Peru. It breeds colonially in burrows and feeds by seizing prey at the surface or diving or plunging for prey items. This species frequently attends trawlers offshore, and the increasing availability of offal may be responsible for recent population increases.