Life Cycle of the Emperor Penguin

from the Ray I. Doan Photographic Collection

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The Emperor Penguin is the only penguin that nests on the ice, all other penguins nest on bare ground. Nests isn't a good word for the Emperors because they don't make a nest, the male Emperor incubates the egg on his feet.

To me it's amazing this bird survives at all, after I've seen first hand what its breeding cycle involves. The problem for the Emperor, with raising its chick, is that the Antarctic summer is too short to get the job done. To get around this problem the Emperor starts in the winter. However, this is a very special winter. This is the Antarctic winter with conditions so harsh they are almost unbelievable.

It goes like this. In the absolute dead of winter the Emperors leave the pack ice and walk in, on the fast ice, to the spot where they'll setup their rookery. This trip in may be up to 75 miles, in the total darkness of the 24 hour winter nights. The spot they select for their rookery is absolutely critical for the survival of their chicks. I'll explain that in a minute.

The kind of place the Emperors seemed to like to setup their rookery was in the vicinity of grounded icebergs. All big icebergs seem to be 600 feet thick. The glacier ice that gets to the edge of the Continent is generally about 600 feet thick. I think this is because the internal pressure in the ice won't allow it to pile up higher than 600 feet without sliding away. Once this glacier ice gets to the edge of the Continent it doesn't stop, it just keeps on going, floating on top of the water. Every once in a while a big piece breaks off and you have a 600 foot thick iceberg. The very large icebergs that are too big to be broken up by wave action are always flat on top. These big bergs are called tabular icebergs.

They have tracked, via satellite, icebergs as big as the state of Rhode Island. These 600 foot thick icebergs float around with about 500 feet underwater and 100 feet out of the water. Whenever an iceberg floats into water less than 500 feet deep it hits bottom and gets stuck. These grounded ice bergs often pile up in one area and form 100 high canyons of ice that are awesome to behold. This was the kind of magnificent setting we found in our visit to the Emperor Penguin rookeries.

The winter temperature at these rookeries regularly gets down to -100º F, which might be so bad, if it weren't for wind chill factor. The birds also have to contend with katibatic winds that often reach 100 MPH. I'm not kidding, they setup their nursery where it's a hundred degrees below zero and the wind blows a hundred miles an hour.

Katabatic winds are not caused by storms but rather the geography of the Antarctic Continent. Antarctica is a huge dome of ice about the size of the United States. It is about 10,000 feet thick, or high, at the center which is approximately the South Pole. There is basically not much wind at the South Pole but the temperature gets down to -130º F in the winter. This creates a large dense mass of cold air sitting on top of a dome. This heavy cold air starts to slide off the top of the dome, by gravity, toward the Emperor Penguin rookeries at the coast. Often times this cold air sliding down from the the South Pole reaches 100 MPH by the time it gets to the edge of the Continent. This is a katabatic wind.

When the Emperors reach the spot they choose for their rookery the birds mate, supposedly with the same partner for life. In practice it seems to be the same partner, as long as the partner shows up on time, otherwise there can be instant divorce. When the female lays her one egg she incubates it for a few hours to a day and then transfers the egg to the male. The female then leaves to feed for the approximately two months it takes the egg to hatch. The male incubates the egg alone. He has a brood pouch over his feet that has bare skin at the back and a flap at the front to cover the egg and keep it warm.

The male must stand for the entire two months, with nothing to eat, and contend with the 100 below temperatures and the 100 MPH winds. Even though he's used to it he doesn't like the wind. The Emperor Penguins huddle together to preserve body heat, and they are the only penguins to do this. This huddling still leaves some birds on the outside and the ones on the windward side definitely want to get out of the wind. The penguins on the windward side will shuffle along, remember they're carrying an egg in their feet, to the lee side of the group. This creates a constant conveyor like motion in the rookery so that each bird has to take his turn in the wind.

After two months the chick hatches and the male, who hasn't eaten anything in months, is still able to regurgitate one meal for the newborn chick. If all goes as planned the female returns just as the chick is born and takes over the feeding chores. If the female doesn't show up almost immediately the male will abandon the chick and return to the sea to feed. His survival depends on his leaving on time.

Now we come to the critical placement of the rookery. If all goes well the an Emperor Penguin chick will be fed 14 times, seven times by each parent. For this feeding schedule the rookery must be in the right place. If the rookery is too far from open water it will take the parents too long to make the trip back and forth to each get in seven feedings.

Another danger of the rookery being too far from open water is a spring snow storm with heavy wet snow. When the chick gets too big to be on its parents feet anymore it is still covered with down. A heavy wet snow will soak the chick. A healthy chick can probably withstand this but a weaker one, that hasn't had enough feedings might not survive. At the Riiser-Larsen rookery we visited there were many more adults than chicks and there were hundreds, if not thousands, of dead chicks. Our staff speculated that unusually heavy ice might have made the rookery too far from open water and caused the deaths. At a healthy rookery there is normally three chicks for every adult, as most of the adults will be out to sea feeding.

The ice where the Emperors have their rookery will, by summer, break up and float out to sea. If the rookery is placed to close to open water, the ice may break up and take the chicks away before they've been fed enough to survive. In this case the whole colony will be lost. Once the ice breaks up and drifts away the chicks are on their own, no more free lunches. At that stage the chicks have not yet molted into their adult feathers so they can't go into the water to feed themselves. If they've had their proper number of feedings they make to adulthood, if they haven't been fed enough times they normally don't survive.

Emperor Penguin research has shown that about 50% of the chicks that hatch manage to fledge and get to sea. Of these about 17% return to the rookery to breed, at about age five or six. Of the breeding age Emperors about 95% return the next year. No one knows how long Emperor Penguins live but they are quite certain they live to at least 50 and possibly 80 years of age. Their long lives enable them to maintain their population with such high infant mortality rates.

Some of our ship's staff were analyzing the Emperors regurgitation's and found the Penguins were mainly feeding on squid. This conflicts with published literature on Emperor Penguins that states their diet is 95% fish. Recent research on Emperors has included attaching depth recorders to Penguins. From these scientists were amazed to see an Emperor Penguin that dove to 2,200 feet deep.

Another interesting Emperor Penguin tidbit is the finally solved mystery of the out of place rocks! Antarctic researchers had long puzzled over the pebbles they found on floating ice that they thought came from glaciers. The problem was they couldn't find the source for the type of rocks they were finding. It was finally discovered that the pebbles came from Emperor Penguins. They learned all Emperor Penguins have stones in their stomach equal to 5% to 8% of their body weight. Apparently they pick them up diving to the bottom to act as buoyancy compensation. When they have long distances to travel, to their rookery, they regurgitate some of the stones to lighten their load.

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This page was last updated: March 15, 2008