Huddling Away the Cold

The tight huddling among emperor penguins is a key energy-saving mechanism that allows them to endure their extremely harsh conditions.

These South Pole penguins, which are free ranging in their colony, spend about 50 percent of their time in dense huddles and drop their average metabolic rate by 25 percent. Researchers questioned whether this drop is due to a process similar to hibernation.

Entering into the colony with bulb thermometers, earlier investigators had found that huddling penguins maintain a lower rectal temperature than birds which were isolated from the colony. However, a sustained drop in deep body (core) temperature would be in direct conflict with the requirements for successful egg incubation. Therefore, energy savings accrued from huddling might rely on mechanisms other than a lower body temperature.

Researchers observed penguins at the emperor penguin colony of Pointe Géologie, near the French station of Dumont d'Urville, Adélie Land, Antarctica between April and August 2001. They found that the metabolic rate in dense huddles may become depressed.

The ambient temperature in a dense huddle increases yet there is no rise in the body temperature of these birds. Researchers believe that a possible explanation for the constancy (or slight decrease) of core temperature inside the dense huddles, in contrast to the expected temperature rise, is the depression of metabolic rate. Such depression could be achieved by entering sleep. In fact, during tight huddles, birds were observed with their eyes closed. It is known that the proportion of sleep increases during the fast of emperor penguins, and that sleep is associated in penguins with an eight percent drop in metabolic rate.

---LiveScience Staff

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Credit: The American Physiological Society