Dead seabirds washing ashore along the Bay of Plenty coast and north of Gisborne starved to death, experts say.
The broad-billed prions (Pachyptila vittata) are normally found off the Otago coast, Chatham Islands and lower Tasman Sea, where upwelling of currents provide a rich source of plankton on which they feed.
Necropsies on the dead birds were carried out by Massey University vets.
Department of Conservation ranger Anastacia Kirk said it was likely the prions had been pushed out of their feeding grounds by strong southerly winds and, once away from their normal feeding area, had become fatigued, emaciated and unable to return south.
"Two days of strong northerly winds averaging 65km/h in the Bay of Plenty may have pushed these birds inland.