The nesting rookeries often contain thousands of birds. Some species, such as the emperor and king penguins, make no formal nest, but incubate the single egg by holding it on the feet for the entire period of incubation, which, in the king, is known to last about 52 days. During this period the male and female take turns holding the egg, relieving each other at intervals which, in the Edinburgh Zoo, where several king penguins have hatched, ranged from half a day to more than a week. Other species make crude nests that may be anything from a shallow depression in the soil, or a burrow, to a jumble of rocks. Until then they are fed by their parents, by regurgitation.
Penguins feed on squid, fish, and crustaceans.
The voracious sea leopard and the Antarctic skua are the major enemies of the bird-apart from man, who has decimated or all but exterminated some colonies by robbing them of their eggs.