Why do some animals hibernate and others don t

Thanks to Henryn for this question.

Some animals migrate to winter-feeding grounds. Others stay and adapt: the red fox grows a thicker coat and changes its summer diet of fruit and insects to more readily available small rodents.

Lastly, some animals hibernate, decreasing their body's energy needs, and therefore food requirements, to a bare minimum.

Q. What happens to an animal when it hibernates

A. The animal's body temperature drops to almost freezing and its heartbeat slows down to just a few beats per minute. Hibernating animals are hard to wake and appear to be dead.

To prepare for hibernation an animal eats large amounts of food during late summer and early autumn to build up its fat reserves. Hibernators have two types of fat: white fat and brown fat. White fat acts as food and insulation, whereas brown fat forms patches near the animal's brain, heart and lungs and warms up these vital organs when it's time to wake up.

Q. How does an animal know when to hibernate

A. The scientists are still out on this one, although some things are known. Hibernating animals have a morphine-like substance in their blood, known as hibernation inducement trigger or H.I.T. for short, which seems to activate the hibernation process when the days become shorter and colder.

Researchers have also discovered two 'hibernation' genes both of which appear to control the use of foodstuffs by the body.

Q. Do hibernating animals sleep continuously

A. Every animal hibernates in different ways. True hibernators, which tend to be small mammals, reptiles, amphibians and insects, undergo a distinct drop in heart rate and a body temperature and are very hard to wake up.

Larger mammals enter into what is known a state of dormancy. Though their heart rate slows, their body temperature doesn't drop as dramatically as true hibernators and although they sleep deeply they are quite easily aroused and become active during warmer spells.

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by Lisa Cardy