Abstract
At least 50% of the yellow eyed penguin (Megadyptes antipodes) breeding population of 240 died on Otago Peninsula during the summer of 1990. Penguin chicks and non-breeding birds were not affected. A large number of laboratory investigations were carried out on the dead birds. Infectious agents, chemical and biological toxins, and starvation were ruled out as the cause of death. A description of the outbreak and details of the tests carried out was given.