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Hibernation - which animals hibernate?

c Danny Green

A guide to species that hibernate in the UK

As the dark days draw in and temperatures begin to drop, many of our favorite species will be collecting fat reserves to survive the coming months, or else preparing to hibernate and avoid the harshest weather.

 

So, what actually happens during hibernation?

Hibernation is where some animals enter a state of almost total inactivity during the winter months. They do this by slowing their heart rate to be up to 10x slower, and lowering their body temperature too. They also lower their metabolism so they don't waste vital nutrients needed to maintain their bodies throughout the winter.

All this means that they’re able to survive for long periods without eating, although they can occasionally wake up for short bursts – on milder days - to look for extra food and go to the toilet. Their bodies have also adapted to wake them up from their dormant hibernating state if they are in danger of freezing due to drastic temperature drops – a useful survival tactic indeed!

Surprisingly, the only mammals that truly hibernate in the UK are hedgehogs, dormice and bats. Other species, such as badgers, just enter a period of lower inactivity instead. People just assume these species have hibernated because they are much less likely to be spotted.

Hibernating mammals in the UK

Hedgehogs

Hedgehogs eat as much as possible during October and November to prepare for hibernation, as they need to weigh between 500-700 grams in order to have the best chance of survival. Once they have reached the appropriate weight, and the average temperature has dropped to around 5°C, hedgehogs will be on the hunt for the perfect hibernation spot. They may hibernate under compost heaps or under garden sheds or decking, and sometimes they will collect leaves and twigs to create the perfect hibernation spot.

Why not help out our prickly pals and provide hedgehog food (not milk as hedgehogs are actually lactose intolerant) and don’t disturb compost heaps or similar piles during the coming months.

Fun fact - A hedgehog’s heart rate is usually around 190 beats per minute but drops to just 20 during hibernation

Dormice

If you’ve seen any dormice lately, you may have noticed that they’re looking a lot fatter than usual. That’s because dormice lose half their weight during winter, so to make up for it they eat as much as possible beforehand, becoming twice their normal size in preparation.

Dormice begin to hibernate between October and November, and they won't emerge from their tiny woven nests until April. You may spot their nests under logs, moss or amongst dead leaves at the base of hedges, as dormice will choose a moist place to hibernate so that they don’t become dehydrated (water vapor is lost as they breathe) and so their fat reserves will last longer.

Bats

During November, bats will hunt for appropriate hibernation spots, known as roosts. They will often choose underground caves, but can also roost in hollow trees, roofs and bat boxes, as long as the roosts are cool and remain at a constant temperature.

Bats are particularly well adapted to hibernation. They are able to slow their breathing to only five breaths a minute in order to reserve energy. In fact, some species can last an hour without breathing at all!

Bats mate during the autumn, just before hibernation. Interestingly, the females have adapted to store the sperm and not become pregnant until the spring, after the hibernation period, when there is enough food to support the pregnancy.

True hibernation vs a State of Torpor

During hibernation, animals will likely not leave their nests/ hibernation spots all winter, whereas other animals will technically still hibernate, but only for very short periods of time. This is known as a state of ‘torpor’, like a mini hibernation which reduces energy requirements during the coldest days.

Badgers are a great example of a species that goes into a state of torpor. They will retreat into their setts during cycles of torpor that only last for around 29 hours, and survive there without food when the weather is too harsh to venture outside. Other species that go into torpor include squirrels and amphibians.

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