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Getting to know our hibernating mammals

North Cliffe Wood autumn colour (c) Simon Tull

As the days get colder, Yorkshire's wildlife species are building up fat reserves and getting ready for winter. But did you know there are only three mammals in the UK that truly hibernate?

I’m sure many of us wish we could crawl into a cosy burrow and spend the winter in hibernation. Sadly, as humans, our bodies lack the necessary metabolic adaptations to make that dream a reality.

In fact, there are only three mammals in the UK that enter a true state of hibernation; bats, hazel dormice and hedgehogs.

What is hibernation exactly?

Hibernation is a process that helps animals to survive during cold winter months, when food and water is harder to find. Whilst entering a state of prolonged inactivity, hibernating animals lower their heart rate, slow their breathing, and even drop their internal body temperature. By decreasing these bodily functions, hibernating animals can survive using far less energy.

While bats, hedgehogs and dormice are the only mammals that hibernate, some invertebrates such as queen bumblebees and butterflies also go into hibernation for the winter. Other amphibians, like frogs and toads, go into a state of 'torpor'. This is somewhere between a deep sleep and hibernation, marked by a decrease in body temperature. 

Hazel dormouse curled up in a ball inside a cosy looking nest - Terry Whittaker/2020VISION

Hazel dormouse - Terry Whittaker/2020VISION

Hazel dormice

In the same way that yawns are contagious, the image of a snoozing dormouse, curled up in a warm cosy ball, makes most people want to close their eyes and drift off to sleep.

These gingery rodents have a real knack for napping and can spend as much as five months of the year in hibernation! In fact, although the exact origin of the name dormouse is unclear, it’s thought to stem from the French word ‘dormir’ which means ‘to sleep’.

Interestingly, hazel dormice spend most of their waking lives hidden high up in trees away from predators, but prefer to hibernate at ground level, normally at the base of trees, inside logs or hidden beneath fallen leaves.

A brown long eared bat emerging from between some roof tiles - (C) Tom Marshall

Brown long eared bat - (C) Tom Marshall

Bats

Unlike most other mammals (that breed in spring), bats begin their breeding season in early autumn.

From September onwards, bats from different colonies will gather in large swarms to look for a mate and find a suitable hibernation roost – often using man made structures like mine shafts or church spires.

Fascinatingly, although bats breed in autumn, females are able to delay fertilisation and won't begin pregnancy until they wake back up in spring.

A hedgehog in a back garden

Hedgehog - (C) Jon Hawkins, Surrey Hills Photography

Hedgehogs

Depending on weather conditions, hedgehogs will begin hibernation from as early as November or as late as January. In the run up to hibernation they’ll find a quiet spot to build a nest, often under hedges, sheds or even compost heaps.

Although hibernation lasts until March, it’s not unusual to see hedgehogs moving around and building new nests throughout winter months.

Wood piles also make ideal places for hedgehogs to hunker down for winter, so remember to thoroughly check winter bonfires for sleeping hedgehogs before you light them!

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