Recognition is key for a pair's survival and the survival of their offspring. Pair bonds form quickly, and mates recognize each other by wing-flapping, neck raising, and other displays. Such exuberance is contagious. Often when one pair starts to greet, the excitement ripples through the colony, as if the birds are doing a strange form of the wave. On such open colonies, nests consist of scraped depressions lined with small rocks, bones, or grasses.
Pairs often fight over stones, precious nesting materials that are regularly stolen by neighbors.
In areas where all three of these species mingle, varied behaviors probably reduce competition for nest sites and food. Unlike other penguins, which usually lay two eggs, these birds lay a single egg that is incubated under skin folds between their legs. The eggs rest on the birds' legs, and can be shuffled along the ice or ground for short distances. While most penguin species split parental duties equitably, male emperors take the penguin prize for parental sacrifice. Many species nest near productive waters during warm months, but not emperors.