Of the 17 species of penguins, only emperor penguins breed during the extreme Antarctic winter, when temperatures can drop to below -50C and winds can reach 300 kilometers per hour. The total number of emperor penguins is unknown because new colonies are still being discovered, but population estimates range from 135,000 to 175,000 breeding pairs, living at about 40 sites on the sea-ice margin of Antarctica. Seven of these colonies are in the Ross Sea, where U.S. scientists have been studying them since the early 1960s.
The breeding cycle of emperor penguins begins in early April, when the adults return to their traditional nesting sites. After laying one egg, the female leaves the colony, traveling as much as several hundred kilometers to feed at sea. The male emperor incubates the egg throughout the dark winter, keeping it balanced on his feet and protected under a pouch of skin. The males huddle in large groups for warmth, fasting the entire time. By the time a chick hatches, the male may have lost up to half his body weight. The female returns in mid-July with the chick's first meal, allowing the male to travel for food and beginning a cycle in which the adults alternately feed and guard the chicks. Because the emperor penguin chicks hatch in early spring, they will have the entire summer to be fed and to grow to maturity before the next winter sets in. Even so, only 20% of the chicks will survive their first year in the harsh Antarctic environment.
Innovative techniques have been used to study these amazing birds, the largest of the penguin species. Tiny satellite transmitters, glued to the birds' feathers, enable scientists to track their movements to ice-free feeding areas during the summer. Although scientists assumed that the birds would feed near their colony, satellite data surprisingly showed that the birds routinely traveled hundreds of kilometers during 2- to 3-week feeding trips.
Depth recorders have shown that emperors dive deeper than any other known bird. They can dive to depths of up to 630 meters, where the pressure would crush human lungs. No one knows exactly how the birds survive or how they find their food in complete darkness.
There are many other unknowns about the emperor penguins, including how they develop so rapidly the ability to dive to great depths. Research has shown that the oxygen storage capacity of an adult emperor's muscle tissue is about 12 times that of a chick's. Yet, the chicks do not enter the sea until summer's end, when they head out into the ocean on their own. Apparently, they develop the unique metabolism of a deep-diving aquatic animal almost overnight, a process not at all understood by scientists. Continued research should bring some answers to these and other puzzling questions about the most majestic of Antarctica's residents.