Like other Procellaria petrels, these are sturdy-looking birds. Westland petrels breed at a hillside colony near Punakaiki on the West Coast, and are one of the few petrel species still breeding on the mainland. As they are among the largest burrowing petrels, they are less vulnerable to predation in the nest than smaller petrels, but are still vulnerable to larger predators such as dogs and, to a lesser degree, cats, weka, large rats and mustelids.

Westland petrels were unknown to science in 1945, when the pupils of the small country school at Barrytown, Westland, wrote to Robert Falla, director of the Canterbury Museum in Christchurch, in response to his radio broadcast about muttonbirds. Their claim that the local ‘muttonbirds’ laid their eggs in May, not in November, led Falla to realise that these birds were different. The children showed him the colony, and Falla concluded it was a new subspecies of the black petrel. It was subsequently considered a separate species.