The two largest and most colorful species, the king and emperor penguins, are both included in the genus Aptenodytes. Unlike other penguins which typically produce two-egg clutches, both lay a single egg which is incubated on top of the feet and covered by a muscular fold of abdominal skin. The emperor penguin is unique in that it breeds during the height of the dark Antarctic winter; only the males incubate for the entire incubation period of 62 to 67 days; and colonies are typically located on the annual fast ice, thus the emperor penguin is the only bird (under normal conditions) never to set foot on solid ground. The fasting period of 110 to 115 days endured by incubating males is the longest for any bird
The smaller but more colorful king penguin A. patagonicus, of subantarctic regions, weighs obertson nearly 20 kilograms (44 pounds) and is capable of producing only two chicks in a three-year period.
The chicks spend the winter in large groups known as colonies where they are fed sporadically, and many perish. The chicks require nine to thirteen months to fledge, the longest fledging period of any res bird. Formerly exploited for their oil, most king per penguin colonies have recovered since being given legal protection.
The Adelie, gentoo and chinstrap penguins are collectively referred to as the long-tailed penguins. The Adelie penguin Pygoscelis adeliae is essentially restricted to the Antarctic and may be the most numerous of the penguins with a population of many millions. The chinstrap penguin P. antarctica occurs in an area known as the Scotia Arc, extending from the tip of the Antarctic Peninsula and including the South Shetland, South Orkney and South Sandwich islands, and South Georgia.
The gentoo penguin P. papua inhabits mainly the subantarctic although some breed along the north coast of the Antarctic Peninsula. All three species nest during the southern spring and summer, October to February.
The migratory Adelie penguin winters in the pack ice, whereas wintering chinstraps favor open water. Some gentoo penguin populations remain near their colonies year round but others may disperse widely.
The six species of thick-billed crested penguins (genus Eudyptes) are essentially circumpolar throughout the subantarctic, and adults are characterized by prominent orange or yellow crests. All species lay dissimilar-sized two-egg clutches, and although some (at least three species) may hatch out two chicks, none is capable of fledging both young. Several species have very restricted breeding ranges for example, the royal penguin E. schlegeli at Macquarie Island, and the Snares Island crested penguin E. robustus only at Snares Island.
The four species of basically non-migratory temperate and tropical penguins within the genus Spheniscus span the greatest latitudinal range: the New World species extend from the Galapagos Islands south to the tip of South America and the Falkland Islands. The black-footed penguin S. demersus lives in South African and Namibian waters. Most spheniscids are burrow-or crevice nesters, but at some crowded colonies they may nest on the surface.
The burrow-nesting little blue or fairy penguin Eudyptula minor of Australia and New Zealand is the smallest of the penguins-up to 30 would be required to equal the weight of one large emperor penguin. The yellow-eyed penguin Megadyptes antipodes of New Zealand is the most endangered of all the penguins, with possibly fewer than 4,500 individuals still extant, a decline of nearly 80 percent since the 1950s and 1960s. Unlike most other penguins, nesting yellow-eyed penguins are not social, and if pairs are not visually isolated from one another they will fail to rear offspring. The loss of suitable nesting habitat and the introduction of terrestrial predators have had a damaging impact.