Dormice are rodents, but they are not ordinary mice: the hazel dormouse belongs to the separate family Gliridae. This small, mostly nocturnal British species climbs through woody vegetation, eats different foods through the seasons, and hibernates in a ground-level nest; it is also protected and declining in the UK.
Here are 10 facts, focused mainly on the hazel dormouse. Other dormouse species can differ, so these details should not be assumed to describe the entire family.
1. A dormouse is not an ordinary mouse
The hazel dormouse (Muscardinus avellanarius) is a rodent in the family Gliridae, not the family of ordinary mice. Its name may sound mouse-like, but it is a distinct kind of rodent.
2. It is tiny and has a furry tail
The Mammal Society gives the hazel dormouse a body length of 60–90 mm and a tail length of 57–68 mm. Adults weigh 15–26 g, though they can weigh up to 43 g before hibernation. Its orange-yellow fur, large eyes and thick furry tail are characteristic features.
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3. It is mostly nocturnal
Hazel dormice forage at night and spend the day in nests. They climb among branches and other woody vegetation, using their agile habits to move through the places where they find food and shelter.
4. Its menu changes with the seasons
Hazel dormice eat flowers, pollen, fruit, insects and nuts. The Woodland Trust describes a seasonal pattern: flowers in spring, caterpillars in summer, and nuts, seeds and berries in autumn. The menu varies with what is available.
5. Connected woody cover matters
Hazel dormice use woodland and overgrown hedgerows. Diverse vegetation can provide food across the active season, while gaps in woody cover can make movement difficult for an animal that spends much of its time climbing. Woodland and hedgerow restoration and dormouse-friendly management are among the conservation measures identified by the Woodland Trust.
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6. Hibernation and torpor are not the same
Winter hibernation is a prolonged seasonal state. Torpor is a shorter energy-saving state that can occur at other times, for example when cold or a shortage of food prevents a dormouse from foraging. The Mammal Society says hazel dormice may spend three-quarters of the year “asleep”; treat this as a broad description, not a fixed schedule for every animal.
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For hibernation, hazel dormice move down from trees and nest on or just under the ground, including in leaf litter or a hollow. Wildwood describes a tightly woven winter nest and a curled posture with the tail over the nose. Avoid disturbing vegetation or nests to look for one.
8. Litters are small, and breeding varies
Hazel dormice usually have one litter a year, though a second is occasionally reported. The Mammal Society describes litters of about four young, while the Woodland Trust gives a usual single summer litter of four to five. Weather can affect breeding success.
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9. Hazel dormice are protected and declining in the UK
The Mammal Society describes the hazel dormouse as strictly legally protected. The Woodland Trust reports an estimated 52% decline in hazel dormouse numbers between 2009 and 2018. This is a period-specific UK estimate, not a current population count or a statement about dormice worldwide.
10. Habitat management can help
The Woodland Trust identifies woodland and hedgerow restoration, dormouse-friendly management and nest boxes as conservation measures. The Mammal Society also highlights diverse woody vegetation and coppice management. Hazel dormice are protected, so leave handling, trapping, nest inspection and other potentially disturbing work to appropriately qualified people.
Hazel dormice and edible dormice in Britain
The hazel dormouse is native to Britain. The edible dormouse (Glis glis) is a separate species introduced at Tring Park in 1902; the Forestry Commission says it is now mainly found within about 35 km of that area. The two species differ, and facts about one should not automatically be applied to the other.
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| Feature | Hazel dormouse | Edible dormouse |
|---|---|---|
| Status in Britain | Native | Introduced at Tring Park in 1902 |
| Where found | Woodland and overgrown hedgerows | Mainly within about 35 km of Tring Park, according to the Forestry Commission |
| Conservation context | UK Vulnerable, according to the Mammal Society; protected | A distinct species with a different UK status and distribution |
Frequently Asked Questions
What is a dormouse?
A dormouse is a rodent in the family Gliridae. The hazel dormouse is a small, mostly nocturnal species native to Britain.
Are dormice mice?
They are rodents, but dormice are not ordinary mice. Hazel dormice belong to Gliridae, a different rodent family.
How long do dormice hibernate?
The dossier sources describe hazel dormice as hibernating through winter but do not give a fixed duration. They may also enter shorter torpor at other times, so a single number should not be treated as a universal schedule.
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What do dormice eat?
Hazel dormice eat flowers, pollen, fruit, insects and nuts. Their food changes with the seasons and what is available.
Where do hazel dormice live?
In Britain, they use woodland and overgrown hedgerows, especially woody vegetation that offers food and connected routes for climbing.
Are hazel dormice protected in the UK?
Yes. The Mammal Society describes them as strictly legally protected. Do not handle them or disturb nests; check official local guidance before any work that could affect their habitat.
Are edible dormice native to Britain?
No. The Forestry Commission says edible dormice were introduced at Tring Park in 1902 and are now mainly found within about 35 km of that area.
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