Yellow-eyed penguins are forest or shrubland nesting birds, usually preferring to nest in a secluded site and backed up to a bank, tree or log. Although they nest in loose "colonies", yellow-eyed penguins do not nest within sight of each other. They live and breed around the south-east coast of the South island, on Stewart island and in the sub-antarctic Auckland and Campbell islands.
Nest sites are selected in August and normally two eggs are laid in September. The incubation duties (lasting 39-51 days) are shared by both parents who may spend several days on the nest at a time. For the first six weeks after hatching, the chicks are guarded during the day by one parent while the other is at sea feeding. The foraging adult returns at least daily to feed the chicks and relieve the partner.After the chicks are six weeks of age, both parents go to sea to supply food to their rapidly growing offspring. Chicks usually fledge in mid February and are totally independent from then on. Chick fledge weights are generally between 5 and 6 kg.First breeding occurs at 3-4 years of age and long term partnerships are formed. Yellow-eyed penguins may live for up to 24 years.
Yellow-eyed penguins feed on a variety of fish including opal fish, silverside, sprat, aruhu and red cod. Arrow squid is also important in their diet. Feeding is usually done near the bottom, at depths of up to 160m and as far as 50km off shore. Dive times are up to 3.5 minutes.
In spring 2004, a previously undescribed disease killed off 60% of Yellow-eyed Penguin chicks on the Otago peninsula and in North Otago. The disease has been linked to an infection of Corynebacterium, a genus of bacteria that also causes diphtheria in humans. It has recently been described as diphtheritic stomatitis. The loss of coastal forest has played a part in the decline of the yellow-eyed penguin on the NZ mainland, but the biggest threat to the survival of the species is introduced mammalian predators. Wild cats, ferrets and stoats often kill chicks and take eggs. Adult penguins all too often fall victim to dogs.