Question: why don't all animals hibernate?

Mike Ambler answered on 12 Nov 2018:

Hi Caitlin,

That’s a great question. I would say that animals generally hibernate if they live in a place where there is a long period of the year in which there isn’t enough food to eat (like winter in the arctic), or they do short hibernations (called torpor) because they are so small that keeping themselves warm takes more energy than they can find in food. Small animals have to spend more energy per gram body weight keeping warm than larger animals (because they have more surface area to body mass). This means that when it gets cold, if there isn’t much food around then they might not be able to keepthemselves warm, so they switch off. These small animals tend to just do it for a short period until it warms up a bit (like overnight, then warming up in the morning).

The risk with hibernating or going into torpor is that the animal is at risk from predators (animals are very dopey or deeply asleep when hibernating), or they might be missing out on the chance to mate (and the chance to mate is an important factor that determines the success of an animal), so it is only worth doing if it is really necessary.