JUVENILE king penguins may huddle together not for warmth, but to get a good night’s sleep. The penguins appear to be able to conserve energy when they need to by allowing their body temperature to drop.
Yves Handrich of the University of Strasbourg, France, and his colleagues inserted temperature sensors into several organs in 10 chicks in the Crozet Islands of the Southern Indian Ocean, then let them go about their daily lives for about seven months. They found that parts of their bodies dropped by up to 15.7 °C when they were inactive, local temperatures fell or when fed cold meals.
The ability to survive despite large drops in body temperature – known as heterothermy – probably helps the penguins live through long winters. “Reducing body temperature even by one degree provides a considerable saving in energy expenditure,” says penguin physiologist Lewis Halsey of Roehampton University in the UK.
Small mammals and birds can allow their body temperature to drop in this way, but it has never been seen in an animal this large. Until now, the largest known heterotherm was the buzzard, weighing up to 800 grams. Coming in at up to 10 kilograms, the king penguin chicks are enormous by comparison.
The huddles may help juveniles rest undisturbed and escape predators, says Handrich.