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Hazel dormouse (Muscardinus avellanarius)

Sleepy, charming, undeniably cute. This minute mammal needs trees to survive and is seriously endangered.

The hazel dormouse hibernates on the ground during the winter months.

Credit: Wild Dales Photography / Alamy Stock Photo

The hazel dormouse often nests in hollow tree branches.

Credit: Arco Images Gmbh / Alamy Stock Photo

Quick facts

Common names: hazel dormouse, common dormouse

Scientific name: Muscardinus avellanarius

Family: gliridae (dormice)

Habitat: woodland, hedgerows

Diet: insects, flowers, nuts, seeds and berries

Predators: owls, domestic cats, badgers

Origin: native

What do hazel dormice look like?

With a body length of just 6–9cm and a tail of similar length, these cute creatures are so small that chances of spotting them are very rare. They have soft golden-brown fur, big black eyes and a long, feathery tail. They weigh no more than 40g and are at their heaviest just before hibernation.

What do hazel dormice eat?

The diet of a hazel dormouse varies depending on the time of year. In autumn, they will feast on nuts, seeds and berries, in order to put on enough fat for them to survive the winter. Once they emerge from hibernation, they will eat the blossoming flowers of trees such as hawthorn and oak, also taking insects like caterpillars when summer arrives.

Credit: Marko König / Alamy Stock Photo

How do hazel dormice breed?

Hazel dormice usually have a single litter of four to five young each summer. The young are born pink, completely hairless and blind, in a nest made from grass and bark, usually located among tree branches or in a hedge. They are covered in pale grey fur after around 12 days, and can see after 18 days. The young begin foraging with their mother at around three weeks old, leaving the nest after roughly six to eight weeks. Their fur stays grey until they are around a year old and sexually mature, when it changes to a golden-brown hue.

How do hazel dormice hibernate?

After gathering up their fat reserves in autumn, hazel dormice will begin hibernation in winter. As the weather turns cooler they will move down from the trees to ground level, creating a tightly woven nest around the size of a tennis ball. They will curl up in this ball with their tail wrapped around their face and body to keep warm.

During periods of cold weather outside of winter, hazel dormice can actually go into a state of deep sleep called ‘torpor’, similar to hibernation, to conserve energy. They can spend as much as seven months of the year asleep.

Credit: iStockPhoto.com / Szymon Bartosz

Where do hazel dormice live?

Dormice prefer the new growth of woody vegetation that arises after woodland management such as coppicing, ride widening, thinning or glade creation. In the UK, they tend to favour old coppice woodland but they’re also found in scrubland, old hedgerows and sometimes conifer plantations. Their range has shrunk significantly and they’re now confined predominantly to southern England and Wales with a few scattered populations in the Midlands, Wales and Lake District. Even where dormice remain, their distribution is patchy. 

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Signs and spotting tips

You would have to be incredibly lucky to spot a dormouse in the wild, as these tiny creatures are very rare and spend most of their time either asleep or high up in the trees. You might spot some signs of them however. Look out for hazelnuts with smooth circular holes in the shell – these have probably been nibbled on by dormice!

These cute creatures are seriously under threat.

Credit: Kenneth Watkins / WTML

Threats and conservation

The dormouse population is in serious danger, with numbers estimated to have fallen by 52% between 2009 and 2018.

Conservation status of hazel dormouse

Hazel dormouse is protected in the UK under the Wildlife and Countryside Act, 1981. It's a Priority Species under the UK Post-2010 Biodiversity Framework and is listed as a European Protected Species under Annex IV of the European Habitats Directive.

Threats

Habitats loss and fragmentation

The loss of ancient woodland and hedgerows across the UK is thought to be a major reason for this decline, as dormice will not leave the safety of trees to cross large, open spaces. This means populations become isolated, lose genetic diversity and are therefore more vulnerable to extinction.

Inappropriate or lack of long-term woodland and hedgerow management

A reduction in traditional woodland management, such as coppicing, has also impacted the species’ numbers. These methods created ideal habitats for dormice, but are being implemented much less frequently nowadays.

Climate change

Climate change is another big threat to the hazel dormouse. As the winters become milder, they disrupt the species’ hibernation cycle, meaning dormice wake early when sufficient food isn’t available.

How we're helping hazel dormice

The Woodland Trust is working to help conserve this species by managing existing woodland in a dormouse-friendly way, as well as providing nest boxes for the species to use.