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Hazel dormouse

From Tilcayo Cats, the lean encyclopaedia by Tilcayo Knowledge Systems

The hazel dormouse (Muscardinus avellanarius), also called the common dormouse, is a small, nocturnal, tree-dwelling rodent of the dormouse family, Gliridae. It was described by Carl Linnaeus in 1758.[1] On the global IUCN Red List it is assessed as Least Concern, but in Great Britain a 2020 regional Red List assessed it as Vulnerable, and its numbers there have fallen sharply since the 1990s.[2]

Description

The hazel dormouse has orange-yellow fur and a thick, furry tail, which makes it the only small mammal in Britain with such a distinctive tail. It has large eyes and ears, suited to its nocturnal habits, and paws that turn sideways to help it climb.[3] Its head and body measure 60 to 90 mm, with a tail of 57 to 68 mm. Adults weigh 15 to 26 g, rising to as much as 43 g before hibernation, and it can live for up to five years.[4]

Habitat and behaviour

Hazel dormice live in deciduous woodland and overgrown hedgerows, and need a variety of trees and shrubs to provide food through the summer. Woodland coppicing can create these conditions, but cleared areas and wide rides may interfere with their movements, because they live almost entirely in the trees.[5] They spend around six months of the year hibernating in nests below ground. Milder winters can wake them while there is still no food available.[6]

Distribution in Britain

In Britain the hazel dormouse is found mainly in the southern counties of England, especially Devon, Somerset, Sussex and Kent. There are few records north of the Midlands, although it is present in parts of the Lake District and in scattered places in Wales.[7] According to the People's Trust for Endangered Species (PTES), it has died out locally in 14 English counties within its historical range, and in six more it is known only from reintroduced populations.[8]

Conservation status

Global and European

On the global IUCN Red List the hazel dormouse is assessed as Least Concern, in an assessment by R. Juškaitis and A. Gazzard published in 2023.[9] This assessment measures extinction risk. Separately, the species has legal protection: it is listed in Annex IV of the EU Habitats Directive, which covers species "in need of strict protection".[10]

Great Britain

In 2020 a Red List for Britain's mammals, drawn up by the Mammal Society using IUCN criteria, classed the hazel dormouse as Vulnerable. The assessment was based on an estimated 48% decline over 2005 to 2014.[11] In Britain it is protected by law under the Conservation of Habitats and Species Regulations 2017 and the Wildlife and Countryside Act 1981.[12]

The National Dormouse Monitoring Programme, run by PTES, counts dormice in nest boxes at woodland sites. Its index fell by 70% between 2000 and 2022. The index tracks changes in numbers rather than measuring how many dormice there are.[13] A 2023 study by Ellie Scopes and colleagues found that counts of adult dormice fell by 78% between 1994 and 2020. The authors argued that, depending on how the data are modelled, the species could be classed as Endangered in Britain.[14] PTES has said the species should be reclassified as Endangered. Its official status in Britain remains Vulnerable.[15]

PTES links the decline mainly to the loss, degradation and poor management of woodlands and hedgerows, made worse by a changing climate.[16] Nest boxes help them survive and breed.[17] Dormice have been reintroduced to several counties since 1992, including Cheshire, Cambridgeshire and Derbyshire.[18]

References

  1. ↑ "Common dormouse - Muscardinus avellanarius - (Linnaeus, 1758)". EUNIS. European Environment Agency. Retrieved 2026-10-18. Common dormouse - Muscardinus avellanarius (Linnaeus, 1758)
  2. ↑ "Hazel dormouse". The Mammal Society. Retrieved 2026-10-18. GB: Vulnerable England: Vulnerable Scotland: N/A Wales: Vulnerable Global: Least Concern
  3. ↑ "Hazel dormouse". The Mammal Society. Retrieved 2026-10-18. Orange/yellow fur; our only small mammal with a very distinctive thick furry tail. Large eyes and ears (because it is nocturnal); Paws turn sideways (for climbing).
  4. ↑ "Hazel dormouse". The Mammal Society. Retrieved 2026-10-18. Size: 60-90mm, tail 57-68mm ... 15-26g in adults, up to 43g before hibernation. Lifespan: Up to five years.
  5. ↑ "Hazel dormouse". The Mammal Society. Retrieved 2026-10-18. The dormouse is found in deciduous woodland and overgrown hedgerows. ... Their principal requirement is for a diverse habitat featuring several different trees and shrubs to provide food throughout the summer. Coppice management of woodlands can create such conditions; but cleared areas and wide rides may interfere with the movements of dormice, because the animals live almost exclusively in the trees.
  6. ↑ "Hazel dormice becoming endangered in UK amid 70% decline, study says". The Guardian. 2023-11-10. Retrieved 2026-10-18. Dormice hibernate for six months in nests below ground but milder winters mean they are increasingly emerging from hibernation when there is no food available.
  7. ↑ "Hazel dormouse". The Mammal Society. Retrieved 2026-10-18. Dormice occur mainly in southern counties, especially in Devon, Somerset, Sussex and Kent. There are few recorded localities north of the Midlands, though they are present in parts of the Lake District and in scattered Welsh localities.
  8. ↑ The State of Britain's Dormice 2023 (PDF) (Report). People's Trust for Endangered Species. 2023. Retrieved 2026-10-18. Dormice are locally extinct in 14 English counties within their historical range; in a further six they are known only from reintroduced populations.
  9. ↑ "Muscardinus avellanarius". IUCN Red List of Threatened Species. IUCN. Retrieved 2026-10-18. Muscardinus avellanarius: Juškaitis, R. & Gazzard, A. IUCN Red List of Threatened Species. Published: 2023-02-08.
  10. ↑ "Common dormouse - Muscardinus avellanarius - (Linnaeus, 1758)". EUNIS. European Environment Agency. Retrieved 2026-10-18. Annex IV: animal and plant species of community interest in need of strict protection. (All species of Gliridae except Glis glis and Eliomys quercinus)
  11. ↑ Scopes, E.; et al. (2023). "Shifting baselines for species in chronic decline and assessment of conservation status. Are hazel dormice Muscardinus avellanarius Endangered?". Ecological Solutions and Evidence. doi:10.1002/2688-8319.12206. the 2020 Red List for British mammals classified hazel dormice as Vulnerable, on the basis of criterion A2b (Mathews & Harrower, 2020), that is, an apparent decline of >30% but <50% (central estimate = 48% decline {{cite journal}}: |access-date= requires |url= (help)
  12. ↑ The State of Britain's Dormice 2023 (PDF) (Report). People's Trust for Endangered Species. 2023. Retrieved 2026-10-18. Hazel dormice are protected in law under the Conservation of Habitats and Species Regulations 2017, and Wildlife and Countryside Act 1981, as amended.
  13. ↑ The State of Britain's Dormice 2023 (PDF) (Report). People's Trust for Endangered Species. 2023. Retrieved 2026-10-18. Between 2000 and 2022, the National Dormouse Monitoring Programme (NDMP) shows the population has fallen by 70 per cent.
  14. ↑ Scopes, E.; et al. (2023). "Shifting baselines for species in chronic decline and assessment of conservation status. Are hazel dormice Muscardinus avellanarius Endangered?". Ecological Solutions and Evidence. doi:10.1002/2688-8319.12206. amounting to an overall decline of 78% (95% confidence interval = 72%–84%) over 27 years, 1994–2020 {{cite journal}}: |access-date= requires |url= (help)
  15. ↑ The State of Britain's Dormice 2023 (PDF) (Report). People's Trust for Endangered Species. 2023. Retrieved 2026-10-18. Under IUCN Red List criteria, dormice are currently assessed as 'Vulnerable' to extinction in Britain, but recent work suggests a higher risk classification of 'Endangered'.
  16. ↑ "Hazel dormice have declined by 70% since 2000, new report finds" (Press release). People's Trust for Endangered Species. 2023-11-10. Retrieved 2026-10-18. Habitat loss and degradation, compounded by climate change, are cited as main reasons for the decline
  17. ↑ "Hazel dormouse". The Mammal Society. Retrieved 2026-10-18. Nest boxes, put up with the entrance facing a tree trunk, are attractive to dormice and help survival and breeding success.
  18. ↑ "Hazel dormouse". The Mammal Society. Retrieved 2026-10-18. they have been success-fully reintroduced since 1992 to several counties (including Cheshire, Cambridgeshire, Derbyshire).
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