Reintroducing the hazel dormouse into the British countryside

The hazel (or common) dormouse (Muscardinus avellanarius) was once widespread across England and Wales. But with the loss of woodland and hedgerows, as well as changes to traditional countryside management practices, populations have declined, and thus they are rare and vulnerable to extinction in the UK. Hazel dormice have golden-brown fur and they are the only small British mammal with a furry tail. They are a priority species in the UK Biodiversity Action Plan and are protected under the Wildlife and Countryside Act 1981.

Through a collaborative project, led by the People’s Trust for Endangered Species (PTES), the Disease Risk Analysis and Health Surveillance (DRAHS) team (based at ZSL) has played a key role in reintroducing captive-bred dormice into the wild to help to combat this decline. In association with the Species Recovery Programme, hazel dormice have been bred in captivity for release since 1993, and over 900 dormice have been released at 23 different sites covering 12 English counties in the subsequent years. DRAHS carries out disease risk management and post-release health surveillance of the released dormice, which are bred by members of the Common Dormouse Captive Breeders Group (CDCBG). 

Currently, the reintroduction programme is striving to improve post-release monitoring methods, as well as ensuring the dormice involved in the captive breeding continue to produce heathy, viable offspring to supplement the wild population. 

ZSL scientists releasing dormice into ‘soft-release’ cages in the Yorkshire Dales National Park

Why we are there

The Disease Risk Analysis and Health Surveillance (DRAHS) project is a collaboration between Natural England and ZSL, has been monitoring the health of 29 species involved in reintroduction programmes since 1989, and provides scientific evidence underpinning the Species Recovery Programme. The hazel dormouse recovery programme is implemented by the People’s Trust for Endangered Species and Natural England, collaborating with the Common Dormouse Captive Breeders Group (CDCBG), Paignton Zoo and numerous wildlife trusts linked to the release sites.

The dormice chosen for the reintroduction are quarantined for about 10 weeks at ZSL and Paignton Zoo. During quarantine, they are weighed weekly and receive a detailed health examination. They are also microchipped, so the quarantined dormice are identifiable. 

Dormouse in quarantine at ZSL

Thanks to the National Dormouse Monitoring Programme (NDMP), dormouse nest boxes in the various reintroduction sites are checked every month. Sick dormice are reported to DRAHS. And if dormouse carcasses are found they are sent to DRAHS where a full post mortem examination is undertaken and reported. Post-release disease surveillance is continuing for all reintroduced populations.  DRAHS has a comprehensive database of pathological diagnoses from free-living dormice and a substantial archive of frozen and fixed materials from pathological examination for retrospective studies. 

Photo of a woodland area with a dormouse nestbox attached to a small tree.
A dormouse nestbox, already set up in the woodland.

The results from the post release monitoring and any subsequent post mortem examinations not only inform the dormouse reintroduction programme but also provides an insight into how small populations of highly threatened species function in the face of changing conditions (including habitat destruction and disease).


  • Ensuring healthy dormice are released
  • Detection of potential disease threats to translocated dormice
  • Developing an understanding of health and disease in reintroduced dormouse populations

Project Information

Key Species

Hazel dormouse (Muscardinus avellanarius)

People Involved

Dr Tony Sainsbury

Dr Tammy Shadbolt

Georgina Gerard

Partners & Sponsors

Partners: People’s Trust for Endangered Species, Natural England, Paignton Zoo, Common Dormouse Captive Breeders Group

News & Blog Links

Dormouse reintroduction day 2021

Dormouse Reintroduction Day 2019

PDF icon SARS-CoV-2 DRA for dormice.pdf (343.39 KB)

Learn more about DRAHS