London: If you think that penguins huddle together for warmth, you're wrong, for a new study says that they do it to get a good night's sleep.

Researchers in France claim that penguins don't freeze, though they do get very very cold -- and they are able to conserve energy when they need to by allowing their body temperature to drop.

A team at University of Strasbourg 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.

The researchers 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 'New Scientist' reported.

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," penguin expert Lewis Halsey of Roehampton University in the UK was quoted as saying.

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 kgs, the king penguin chicks are enormous by comparison.

The huddles may help juveniles rest undisturbed and escape predators, said lead researcher Yves Handrich.

The findings have been published in the latest edition of the 'Nature Communications' journal.