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BiologyThe Westland petrel is one of the largest burrowing petrels, and one of the few petrel species that still breed on the New Zealand mainland, probably as their larger size makes them less vulnerable to mainland predators than smaller petrel species (5) (6). They build large, cavernous burrows in colonies, up to 2 m long, close to steep slopes, cliff edges or trees from where they can take off (7). In May (8), one egg is laid in the burrow and incubated for 57 to 65 days (2). Chicks fledge after 120 to 140 days and then head out to the open ocean, not returning to the colony for five years, and not breeding themselves until, on average, the age of ten (2) (6) (8). When not breeding, they forage out over the ocean, feeding on cephalopods, fish and crustaceans (2). Westland petrels feed primarily by day (8). They most frequently feed by sitting on the water and seizing prey with their bill, but they can also dive well, propelling themselves with their powerful wings (2). Westland petrels are also eager scavengers; they are frequently found following fishing vessels, where they feed on fisheries waste which forms a substantial part of its diet (2) (4).