The species is easily identified by the distinctive pale yellow stripe on the back of its head and around its yellow eyes. The Yellow-eyed penguin is tall and heavy with a long and slender beak. Generally, males and females look similar, though females are somewhat smaller than males. The forecrown, chin and cheeks of the animal are black, covered with yellow markings. The sides of their head and the foreneck are colored with fawn-brown. The tail along with the back is state blue. Dorsal parts of their feet are pink and the ventral parts are black-brown in color. The beak of the Yellow-eyed penguin is red brown and pale cream. The front thighs, the underside of the flippers, chest and belly are colored with white. Young penguins do not have the pale yellow stripe, found in adults. In addition, the eyes and napes of juveniles are paler than these of adults.
The Yellow-eyed penguins inhabit southern parts of New Zealand. The area of their distribution stretches from the south-eastern coast of the South Island, with the highest concentration of the species on Otago Peninsula, through Foveaux Strait to Stewart Island, reaching sub-Antarctic islands of Auckland and Campbell Islands. These penguins construct their nests on slopes, gullies or right on the seashore, usually in small bays or on promontory areas of large bays. They nest in forest or bushes, preferring habitats with flax and lupin communities.
These penguins are sedentary animals, tending to stay constantly in the same area. They will only make short foraging trips, usually not going too far from their territory. The Yellow-eyed penguins are not colonial, in a sense that they do not live in colonies. These penguins are diurnal birds. They spend the greater part of their time feeding at sea. These penguins usually build their nests in solitary places, covered by a bank, tree or log. They nest in loosely organized groups, preferring hidden, secluded places, so, when nesting, they communicate through vocalizations, which help them find their mates and chicks. During the mating season, the Yellow-eyed penguins use shrill vocalizations, when communicating to potential mates.
They are serially monogamous, mating with only one partner during each breeding season, which lasts from mid-August to mid-March. Forming a pair, they build a nest. The female lays 2 eggs, after which both the male and the female incubate the eggs together. The chicks hatch out at an interval of 24 hours. During the first 25 days of their lives, the hatchlings are cared by both parents, who feed them through regurgitation for about 15-25 days. By the end of this period, parents leave, going out to sea for foraging. Chicks of this species do not gather into crèches. Fledging occurs in the middle of February, when the hatchlings are 14 weeks old. Then, at the age of 1 year, they undergo molt, gaining their adult plumage, including the yellow stripe. Sexual maturity is reached at the age of 2 years.
Presently, there are 3 notable threats to the population of these species. These are: degradation of their habitat, presence of introduced predators and climatic changes. Degradation of their habitat is a result of agricultural development within the area of their range, and especially, throughout coastal forests of mainland New Zealand. The penguins suffer from the introduced sheep and cattle that can trample their nests as well as negatively affect the environment by overgrazing. And finally, environmental changes hugely impact the population of these penguins that are exposed to food shortages because of changes of the sea temperature, which, in turn, leads to sharp decline in numbers of prey populations.
The overall number of the Yellow-eyed penguin population is currently decreasing with the estimated population of about 3.400 mature individuals. On the IUCN Red List, the species is classified as Endangered (EN).