HIBERNATE THE WINTER AWAY
Enjoy an extended period of deep sleep while it’s cold
Sleeping through the cold, dark winter might sound like a good idea to some people. And while that’s exactly what certain species of animals do, hibernation is more than just sleep. The entire metabolism of the animal becomes suppressed. Their body temperature falls, while their breathing and heart rate slow. “A bat may normally have a heart rate of around 400 beats per minute at rest, and might reduce this to 11 to 25 beats per minute when it’s in torpor,” says Dr Kate Barlow from the Bat Conservation Trust. “By slowing down their body systems, they use up less energy – a bat may use up only about one per cent of its normal requirements when hibernating.”
Bats don’t spend the entire winter asleep, however. “They will arouse at regular intervals, on average every couple of weeks, using their stored fats as energy to increase their heart rate, breathing and shivering their bodies to warm themselves up until their body temperature is back to a normal level and they are active,” says Barlow. “The reasons for waking aren’t fully understood – it must be important for winter survival, as it costs the bat a lot in energy terms. It may be to allow the bats to feed, as they will often become active on milder winter nights when insects might be flying, to drink, mate or move between hibernation sites.”
While bats may hibernate in human-made structures such as mines and tunnels, other creatures make a nest. The ideal hibernation temperature for the dormouse is one degree Celsius – just warm enough to prevent it freezing – so it weaves a structure of leaves on the ground. They can even go into a state similar to hibernation during spells of bad summer weather when food is scarce.