Hello Dormouse! Meet Britain's Sleepiest Mammal – Home & Roost

Hello Dormouse! Meet Britain's Sleepiest Mammal

Hello Dormouse! Meet Britain's Sleepiest Mammal

Clare Stone |

There are 29 species of dormouse worldwide and 3 present in the UK. But only one, the hazel or common dormouse, is a native species. The Hazel dormouse is an important indicator species, endangered and vulnerable to extinction here in Britain. So let’s find out a little more about dormice and what we can do to help them. 

Dormice In The UK

Like the Hedgehog, the dormouse is an ancient creature. With all 29 modern varieties traceable back to an ancient giant dormouse that existed around 30 million years ago.

There are now three species of dormice present in the UK but only one is native, or indigenous. 

The Garden Dormouse

You don’t want one of these in your garden. Although they may look cute they are not a native species and like the grey squirrel, could provide excess competition to our native wildlife. 

garden dormouse

It’s thought that the garden dormouse might have been introduced to the UK by the Romans for food - before they discovered the more tasty edible dormouse. 

It has been extinct here for centuries though, until recent decades when a few have been found, mainly in the south of England. 

They are thought to be coming over from the continent, where they are fairly common, in lorries and on ferries. The garden dormouse is classed as an alien species under the Wildlife and countryside act, so it’s illegal to release them into the wild and there is no suggestion that they are currently breeding in the wild in the UK. 

This is a good thing as the introduction of any alien species can threaten the ecosystem and being bigger and less selective than our native hazel dormice, they could easily offer unwelcome competition 

The Edible Dormouse

The edible or fat dormouse: glis glis may also have come to the UK with the Romans. Dipped in honey, rolled in poppy seeds and deep-fried they were a prized delicacy at a Roman banquet and are still eaten in parts of eastern Europe.

But despite the name, please don’t be tempted to eat an edible dormouse in the UK now. Even though they are not a native species they are still protected under the wildlife and countryside act and it’s illegal to trap them without a licence. 

Our current population of glis glis were introduced to Tring Park in Hertfordshire by Lord Rothschild in 1902. They quickly established and spread throughout the home counties with population estimates now running at over 20,000. 

edible dormouse glis glis

The edible dormouse looks very like a little fat grey squirrel. And like the grey squirrel, they are becoming something of a pest. They readily enter buildings and cause damage to cables and it’s thought they may cause damage to conifer plantations. So their conservation status is confusing, whilst it’s illegal to trap or kill them without a licence it’s also illegal to release them into the wild. 

The edible dormouse has a unique trick for evading predators. If grabbed by the tail it can shed the fur and skin of its tail and escape. It can only do this once though, as the bare tail bones soon fall off, leaving the animal tailless, but otherwise unharmed. 

The Hazel Dormouse

The hazel dormouse muscardinus avellanarius is our only native dormouse and an endangered species in the UK. They need our help. 

Conservation Status

The Peoples Trust for Endangered Species estimates that the hazel or common dormouse population in the UK is declining by 5.8% per year. So it’s no surprise to find that they are red-listed by the Mammal Society as Vulnerable. 

They are protected under Schedule 5 of the wildlife and countryside act, they are a European protected species and a priority species under the UK Biodiversity action plan. 

So it’s safe to say whether you are a developer, local council, or member of the public, it’s an offence to interfere with, harm or kill Muscardinus avellanarius Hazel dormice.. 

Well Named

It can be hard to actually see a hazel dormouse in the wild for reasons we will come on to shortly. But you can tell a lot about it from its name. 

Dormouse is thought to come from the french “dormeuse” meaning sleeper. And the hazel bit refers not to the sandy brown colour of their fur, but to one of their favourite foods, the hazelnut. The Latin name , muscardinus avellanarius literally translates as “mouse of the hazel trees”.

hazel dormouse  muscardinus avellanarius sleeping

But hazel dormouse isn’t strictly speaking a mouse at all. Although they are rodents their tails are furry, and they don’t have the scaly tail found in mice. Hazel dormice are actually more closely related to squirrels and beavers. 

Recognising Hazel Dormice

It’s not very likely that you will see a hazel dormouse in the wild, partly because they are scarce, and partly because of their lifestyle. 

But they are not hard to recognise. The hazel dormouse is tiny, weighing about as much as a £1 coin with a body length of 6-9cm and another 6cm of fluffy tail. 

The hazel dormouse is nocturnal

They are our only small mammal with a long furry tail, gingery brown like the rest of the fur (juveniles may be more grey in colour). They have prominent round ears that stick up on top of their heads and very large, brownish-black eyes. The Hazel dormouse is nothing if not photogenic!

Where Do Hazel Dormice Live?

In the UK the hazel dormouse can be found mainly in southern England, East Anglia and Wales. The species is rarely spotted north of the Midlands, though there are known to be a few breeding populations in the lake district. They are not present in Scotland.

It was thought that hazel dormice lived almost exclusively in hazel woods. They are difficult to spot and were most often found in the winter by woodland workers coppicing hazel. 

But modern research has been able to confirm that the hazel dormouse can and does live in a much wider range of habitats. Mixed deciduous woodland. Scrub, well-established hedgerows, even conifer plantations and rural gardens can provide a home. 

The dormouse’s essential requirements for habitat are trees with a good understorey of fruiting and flowering shrubs offering enough density for them to move around without coming down to the ground. 

Hazel Dormouse Diet

Hazel Dormice are successional eaters. This means they eat with the seasons. They start in spring with nectar-rich flowers like honeysuckle and hawthorn blossom. In summer they move on to insects and small aphids and as autumn arrives they feast on nuts and fruit. 

though hazelnuts are a favourite food, dormice eat berries too

Hazelnuts are a favourite food and they access the nut by making a very distinctive neat round hole in the shell. Finding the discarded shells in the woods is another way of spotting the presence of dormice - even if you cant actually see the animal. 


It’s not just their small size that makes these creatures difficult to spot - their lifestyle makes them very elusive too. 

Super Hibernators

Like the hedgehog and the bat, hazel dormice hibernate, Boy do they hibernate! In the UK they typically hibernate for at least six months of the year - October to April, to conserve resources during the winter cold and food scarce months. 

Dormouse hibernation is deeper than that of the hedgehog. Body temperature has been recorded dropping below -2 centigrade. And unlike the hedgehog, the hazel dormouse rarely rouses from hibernation to move, eat or drink. This means that before going into hibernation they must eat enough to double their body weight, And hibernation nests must be humid, so the creature doesn’t dehydrate and desiccate during the winter. 

Hazel dormice always hibernate on or under the ground

As well as winter hibernation dormice will sometimes enter a state of torpor during the summer months. They can do this for several hours a day to save energy when food is scarce or weather poor (dormice don’t like to forage in the rain). They often spend many hours during the spring months in a torpid state, which means they mate much later than most woodland mammals. 


Hazel dormice are strictly nocturnal. Sleeping during the day and coming out to live their lives at night. 

During the daytime, dormice build nests to sleep in. These may b in hedgerows. Tree branches or holes in mature trees. They are also happy to borrow old birds nests or sleep in nest boxes. 

the hazel dormouse is nocturnal

It’s rare to see a dormouse out in the daytime, but juveniles dispersing from the family home or adults during the mating season may occasionally venture out in daylight. 


Dormice spend most of their lives above the ground. They are extremely agile, using their whiskers, eyesight and hearing to navigate through the branches at night. They typically forage at between 2 and 10 meters above ground level. 

Hazel dormice don’t like coming down to the ground as it makes them vulnerable to predators. So trees must be connected by a good layer of undergrowth which allows them to move and feed freely. Thick hedges also enable movement. 

This is why mature, traditionally coppiced woodland is an ideal habitat for dormice. Coppicing allows light to penetrate the tree canopy, so the undergrowth can grow and fruit. If the tree canopy is too thick, no light gets through and the woodland floor becomes bare. Not ideal if you’re a dormouse. 

The only time dormice to like to come down to the ground is during hibernation season in the winter months. Hibernation nests are always built on or just under the ground, as they need to remain moist through winter. 

Family Life

Hazel dormice form long-lasting pair bonds with evidence of the same pair using the same nesting site for successive years. This is very unusual for small rodents. 

They have one sometimes two litters averaging 4 babies in each. The young stay with the mother for six to eight weeks and a mother may occasionally bring two litters together into a family creche. 

Youngsters will eventually disperse and establish their own home ranges. These tend to be quite small with individuals rarely straying more than 70 meters from their nests to forage. 

holes in mature trees are a favourite nesting place for the hazel dormouse

Males have larger ranges and a male range will overlap those of several females. Males can be extremely territorial during the mating season. 

The hazel dormouse is also surprisingly long-lived for a small rodent with an average life span of 5 years in the UK.

Threats to the Hazel Dormouse

So why is the hazel dormouse an endangered species? Well, as so often the case humans are the problem. 

Hazel dormice in the UK have no serious predators. They may be taken opportunistically by other mammals or birds of prey as a tasty snack. But they live at too sparse a density to make them a preferred food for any other species. 

sleepy dormouse

Habitat loss is thought to be the main reason for their decline. The mature, traditionally coppiced woodlands that make ideal dormice habitat now exist in very few places in the UK. 

Likewise, thick, species-rich hedgerows are becoming scarce. 

So although a dormouse doesn’t need a huge range, the habitat is becoming fragmented, making breeding difficult and resulting in individual populations going extinct. 

The Hazel dormouse is also very sensitive to the weather and climate change is disrupting hibernation and breeding patterns. 

How To Help The Hazel Dormouse.

Thankfully there is a lot being done to help the hazel dormouse and there is some evidence of the decline in number slowing. 

Renewed interest in traditional coppicing in many places, but particularly the National Trust, is good news for the dormouse. 

Changes in agricultural policy to encourage biodiversity could see a revival in our hedgerows. 

And reintroduction programmes have been key to bolstering the dormouse population for many years. 

And we can all do our bit to help:

Thanks for Reading

Just like the hedgehog, the hazel dormouse is an important indicator species: habitat that is good for dormice is good for many other woodland creatures. So work that helps the dormouse helps a wide range of our native wildlife too. 

Though they are in trouble they have been supported to avoid extinction by dedicated conservationists for many years. Let’s hope we will now start to see some changes in our land management policies which will allow hazel dormice to thrive again naturally, without too much human intervention. 

Thanks for reading, we hope you’ve enjoyed this article and found it useful. If you have questions or suggestions we would love to hear them. Leave us a comment below.