According to Oliver, this seems to be a stationary species, not having been observed in any numbers far away from its breeding grounds. Off the coast of Stewart Island it associates with the shy mollymawk and like it has developed the habit of attending fishing boats and following them into port, consequently it has become one of the main casualties of long line fishing.
The Northern Buller’s mollymawk returns to the Chatham’s in late September to breed, whereas the Southern Buller’s mollymawk returns to The Snares in mid–December. The chicks fledge in June at the Chathams but August–October at The Snares.
The nest is constructed, after the fashion of other mollymawks, by the bird sitting down on the chosen site from which position it reaches out and loosens the soil all around it or, if the vicinity contains vegetation, this is torn to pieces. The debris is placed under the bird as the nest is built higher and higher. The material is added beakful by beakful and is patted down with the bill. The bird keeps turning slowly and its feathers become very dirty in the process. Most of the nest building is done by the male but both birds share in the incubation.
