Emperor penguins are the largest and heaviest member of the penguin family. Males and females look alike but their songs differ. Measured from the tip of their beaks to the tip of their tails they are approximately 1 m long but when they are upright they stand about 70 cm tall.
Their necks comprising 13 vertebrae are flexible and highly extendable. When an adult pulls in its head, the cervical vertebrae form a strong S-bend and shorten the appearance of the penguin.
The bodies of emperor penguins are cigar shaped and streamlined. The flippers are about 35 cm long and are highly specialised for fast underwater movement of around 14 km/h. Head, chin, throat and neck are black and contrast strongly with the auricular (ear) patches where the colours changes from a deep yellow on the top to a pale yellow to nearly white at the bottom. The upper part of the chest is soft yellow but most of the chest and underside of the flippers are a soft white which is demarcated from the dark grey-blue back by a black stripe. The beak is narrow and long with a curved tip. The mandibles are black and the mandibular plates on the lower mandible range in colour from pink to lilac. The feet and legs are black and the iris is dark brown.
The body mass is highly variable throughout the year. When arriving at the colony in late autumn, the penguins tend to weigh 30-40 kg, sometimes more. During courtship, mating and laying the penguins usually rely on their accumulated body reserves as the ice edge is often too distant to go on regular foraging trips. Most females weigh well less than 30 kg when they depart the colony after laying. Upon their return some two months later they are well fed while the males who have fasted for nearly four months have lost a third to half their body mass and weigh less than 25 kg. At the end of the breeding season, all adults need to fatten again in preparation for the annual moult.
It takes about 5 years for an emperor penguin to acquire its full mature plumage. Juveniles lack the yellow feathers on the chest and the ear patches. Their throats and chins are a soft grey and their beaks are entirely black.
Chicks are covered in soft grey down but their heads are black with a white mask around the eyes.
Because of the remoteness of many of the emperor penguin colonies it is very difficult to establish a global population size. Many colonies have not been visited for several decades and recently found ones still need to be confirmed. There are just over 40 colonies that vary in size from a few hundred to a several ten thousand pairs. The largest known colonies (~16,000+ pairs) are located in the Weddell and Ross seas. Cape Washington, Ross Sea, is the largest known breeding colony where on average some 20,000 chicks hatch.
In 2009, British scientists used satellite images to look for emperor penguin colonies around Antarctica. This technology may proof useful as a tool to monitor remote colonies in the future and enable scientists to obtain much better information on the status of the global emperor penguin population.
Emperor penguin colonies occur right around the Antarctic continent. Most but not all colonies are situated on the fast ice (sea ice that is attached to the continent). About 40 breeding colonies are known to exist. Some of them still need to be confirmed.
The at-sea distribution varies throughout the year. During the breeding season, the penguins need to stay relatively close to the colony (~ 100-200 km) to provision their chicks regularly. However, post breeding, the adults travel much larger distances and move farther north than during chick rearing when they prepare themselves for the annual moult. Fledglings that depart the colonies for the first time travel even farther and can reach latitudes near 54°S.
Emperor penguins are the only vertebrate species that breeds during the Antarctic winter. Colonies start to assemble approximately in April when the fast ice is stable enough to support them. For several weeks, the birds are occupied finding mates, creating pair bonds and eventually mate. The females produce only one egg which is quite small compared to the body size of penguins. Eggs weigh around 460 g which is less than 2% of the body mass of a 28 kg female.
Since only the male penguins incubate the eggs, the females have to pass over the egg to their partners. It is no easy task to move a roundish egg with a long, narrow beak quickly across the ice onto the partner’s feet! In temperatures of less than -20°C, the eggs quickly freeze if exposed for too long. The males scoop up the eggs onto their feet and cover them with a fold of their skin. Part of this skin fold is feather-free so that the father’s body heat can be transferred directly onto the egg. The incubation temperature is roughly 37°C.
While the females leave the colonies to feed in the pack ice (zone of sea ice made up of ice floes) or in polynyas (ice-free areas in the sea ice area), the males incubate their eggs for about 65 to 70 days. During this period, they cannot hunt and are entirely reliant on the body reserves they deposited before returning to their colonies in late autumn. Although their huddling behaviour makes it possible to stretch out their energy reserve, if these body reserves are insufficient, the males run the risk of either starving to death or having to leave the egg and venture out to sea to feed again.
Of great importance to the incubating males is access to fresh snow. The care of the egg prevents them from going to forage at sea. However, their bodies are still metabolising the energy stores and hence produce waste products. Each time a male defecates water is lost from its body. To make up for this water loss the males need to eat snow.
The females return to their colonies in mid- to late July to relieve their mates. The chicks have usually hatched by then and weigh around 300 g. Their eyes are open and they are capable of some limited locomotion. However, the chicks are not yet able to regulate their own body temperature. Hence, they need to be brooded by their parents for about 50 days. Growth is slow during this time as they chicks need to remain small enough to fit into the brood “pouch”. Both parents share the brooding duties.
The fast-breaking foraging trips of the males vary in duration and depend upon how far the fast ice extends from the colony. It is not uncommon though that the first trip lasts 2-3 weeks. While the males are at sea replenishing their body reserves, the females bond with their chick and feed it on demand for as long as they still carry food in their stomachs. The food consists of small fish, particularly the Antarctic silverfish Pleuragramma antarcticum, Antarctic krill Euphausia superba, and assorted squid.
Around September, the chicks are able to maintain their body temperature at ~39°C. They now start to grow quite rapidly and require so much food that both parents have to provision them. The chicks start to form creches, which offer warmth and protection for predators, such as Antarctic skuas (Catharacta maccormicki) and Southern giant petrels (Macronectus giganteus).
By mid-December, the chicks can reach a body mass of some 20 kg although many are lucky to reach 13-15 kg. How heavy they are in summer depends on how much food their parents managed to secure and how often the chicks have been fed in the previous months. Like their parents they need sufficient body reserves if they are to survive the moult from down to juvenal feathers which will make them waterproof and able to go to sea. The chicks often leave the colonies well before the last bit of down has been shed.
Breeding adults have to decide for how long they continue to feed their offspring. If they abandon the chick too soon, it will perish. If they feed it for too long, they might put their own survival at risk because they need a certain time to forage intensively to get ready for the annual moult. Adults who either did not breed in a given season or who lost their egg or chick early on can be found in colonies moulting already in mid-December. Most breeders though commence their moult in late January. It takes about 3 weeks for the entire plumage to be exchanged. The old feathers are quite worn and are pushed out by the new ones developing underneath the skin. The blood flow to the flippers is increased to the point that their thickness doubles. Growing feathers is energetically expensive and a lot of blood is needed to carry the necessary nutrients into the flippers.
At the end of the moult, the penguins are skinny and often weak. They must return to sea and start feeding again in preparation for the next breeding season.
Meanwhile, the young penguins remain at sea. Not only do they travel vast distances away from their natal colonies, they often swim north and leave the pack ice far behind them. Usually in late autumn they turn back. towards the continent but usually do not return to their colonies until they are sexually mature (~ 5 years old). Only occasionally young penguins are seen in breeding colonies.
Ice breeding emperor penguins can establish breeding colonies only in areas where the fast ice is stable, provides a reliable platform and persists well into summer. That is why breeding colonies of emperor penguins are usually found far south and far away from the edge of the fast ice, which is prone to destruction by wind and waves during storms. Note, however, that three colonies are known to be located on solid land where flat ground is available.
Since glaciers or ice tongues are often near the breeding areas, the colony locations occasionally must shift when ice bergs calve off the glaciers. Even during the breeding season, the penguins are highly mobile and can shift their location up to several kilometres, particularly in the largest of the ice-breeding colonies.