What Animals Hibernate UK?

Darker days and cold winter mornings mean one thing for a few animals in the UK: it's time to hibernate and save energy.

There are only three UK mammals that enter true hibernation, and it's more than just a deep sleep for the winter months. Most other wild animals will enter a state of torpor during the cold weather.

In this blog, we'll go through everything you need to know about the complex process of hibernation and how you can help animals that might be hibernating around you.

What Happens During Hibernation?

The hibernation period is defined as a inactivity that allows animals to conserve energy and survive the cold winter.

Animals prepare by building up body fat reserves by eating as much as they can. In the lead up to winter, hibernating species will look for signs like a lack of food availability, temperature drops, and days getting shorter; these are all indicators that it is time to have their long sleep.

Once it is time, they retreat to a safe spot, like under garden sheds, ground burrows, hollow trees, hibernation roosts, and log piles, and they enter hibernation. The animal's bodily functions slow or become halted. Hibernating creatures burn a reduced amount of energy during the winter months as their body temperatures cool and their heart rate slows, which is where hibernation differs from normal sleep.

It may seem that this is a vulnerable time for these animals, but they give off less scent during this time, so they are harder for predators to find.

When it's time to wake up, hibernating animals can take up to one hour to fully wake up (we know how they feel!). During the period of hibernation, they do get up occasionally for things like moving location, excreting waste, and even snacking.

Types of Hibernation

With only three mammals (bats, dormice, and hedgehogs) truly entering a state of hibernation, you must be wondering what all the other animals that go missing during the cold winter months do. Well, they still enter a state of inactivity to conserve energy, it's just not strictly the same as hibernation.

Torpor

Also known as 'dormancy', Torpor is a period where animals are less active, with reduced bodily functions. Unlike hibernation, Torpor is a short-term state, and it is involuntary.

Animals will only enter a state of torpor if the weather becomes too harsh for them to survive; it's just like a mini hibernation.  In the UK, species like Red Squirrels enter a state of torpor.

Brumation

In colder months, reptiles and amphibians will go into a state of brumation. It is similar to hibernation as it involves long periods and is done to save energy through harsh winters.

Unlike warm-blooded animals, reptiles rely on environmental temperatures to regulate their body heat. During brumation, their breathing and heart rate slow dramatically, and they may go extended periods without eating, although they might occasionally wake and move around on warmer days.

Diapause

Diapause is a state of suspended development. It is the interruption of an insect's development in response to environmental challenges.

It is controlled hormonally and can occur at various life stages, including egg, larval, pupal, or adult phases, for many insects. The peacock butterfly and solitary bees are both species that enter this state.

Mammals that Hibernate in the UK

Bats

In the UK, bats are one of three species that enter a true state of hibernation. They tend to hibernate in sheltered locations such as caves, hollows, bat boxes, and the roofs of buildings, and start looking for the perfect spot in November. 

During this period, their body temperature drops and their heart rate and breathing slow. They can slow their breaths to just five in a minute! Some species can even go an hour without breathing. 

Hedgehogs

During October and November, hedgehogs eat as much as possible to prepare for hibernation. To have the best chance of survival, they need to weigh around 500 to 700 grams!

Once they are around that weight, temperatures have dropped to 5 degrees, and they go on the hunt for their hibernation spot. Compost heaps, under garden sheds or decking, are perfect for this species. 

A hibernating hedgehog's body temperature drops dramatically, and they becomes unresponsive to most external stimuli.

Dormice

The hazel dormouse hibernates at ground level, often in well-insulated nests among leaf litter or under logs. Hibernation typically lasts from October to April. This prolonged torpid state is crucial for survival during periods when there is not enough food.

Before hibernation, dormice eat large quantities of food, often doubling their body weight in fat reserves. This stored fat is their only energy source during hibernation. When the weather turns cold, they can lose up to half of their body weight, making their pre-hibernation feeding period essential for survival.

How to Help Hibernating Animals?

Sometimes, hibernation can be a tough time for wildlife, but there are a few ways we can help!

• During Autumn, make sure there is lots of food left out for hibernating animals. If you know there are local hedgehogs, leave out hedgehog food.

• If you have lots of plants in your garden, try not to cut them back until spring, as they can provide space for insects to diapause. You could also invest in some insect hotels, as solitary bees will seal themselves into the hollow stems.

• As winter comes, leave messy areas of your garden, creating piles with logs, plant matter, and twigs so there's space for hedgehogs to hibernate.

The Effect of Climate Change on Hibernation

Climate change has a growing impact on the hibernation behaviours of many animals. Warmer winters and unpredictable weather can confuse animals, as they rely on environmental clues to begin or end hibernation. As a result, some species may emerge too early when food is still scarce, leading to starvation.

For example, hedgehogs in the UK have been observed waking earlier than usual, while dormice may find their hibernation periods interrupted by mild spells. These disturbances can reduce survival rates by forcing animals to burn through their fat reserves too quickly.