By the beginning of April emperors leave the water and travel large distances over the new pack ice to reach the fast ice along the coast. Here they congregate in flocks of several hundred individuals. In May, the female lays a single egg on the ice and leaves for the open water. Using his beak, the male immediately lifts the egg on to his feet and covers it with his warm egg pouch. The egg is then incubated for three months during mid winter when temperatures may drop to below -50 C and the male does not feed.
Emperors look identical, yet partners always find each other and mate for life.
At a size of about 70 cm and weighing 5 kg they are considerably smaller than emperors. Adelies breed in large colonies on land some yet some pioneers always attempt to breed on the sea ice. Such efforts are doomed as the eggs freeze on the ice nests. As with emperors, adelie males incubate the clutch of two eggs while the females are out at sea feeding. Their prey consists mainly of krill and small fish.