Stuck in the huddle with you

Why did the penguin cross the floe? Scientists know the answer now: to be with his mates. Huddling is essential to survival for male emperor penguins, which go without food for 110 days to incubate their eggs during the bitter Antarctic winter.

During a study of the animals at the beginning of the Antarctic winter, scientists began wondering why it was that the male penguins - which must remain motionless for more than three months in temperatures way below freezing and howling blizzards if their eggs are to stand a chance of hatching - gathered in large groups without resorting to violence.

They have to stay with the egg while the female penguin builds up a store of food. But she only returns to her mate, and her egg, once the incubation is over. That allows the male to leave the group and forage for food again.

In other animals, such a gathering of males would tend to spark off fights, since there would be an advantage in destroying a rival animal's egg and so producing a better chance of there being food to nourish the survivor's chick.

But the team, from the University of Groningen in the Netherlands, found that huddling has distinct advantages for the penguin, which warms the egg between a roll of fat under its stomach and its feet. Being in a group shelters the penguin from the biting wind, meaning that they use 25 per cent less energy than if they were on their own in the open.

Without huddling, emperor penguins would reach "the metabolic status that would trigger refeeding" - as the team described extreme hunger - three weeks before the egg hatched. The size of the group is also important: while being on the outside of any group would never be pleasant, a small group cannot huddle efficiently, the scientists found.

Eventually, the team decided that the penguins' behaviour is possible because unlike many other male animals, they are not territorial. Happy huddling allows them to breed in one of the coldest places on Earth.

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