Bringing the dormouse back to UK woodlands

Liam Fitzpatrick

Liam Fitzpatrick is currently undertaking research for his PhD, where he is examining the risk of avian malaria to birds in the Galápagos archipelago.

Many UK woodlands have been missing an endangered rodent for decades. Liam Fitzpatrick, Pathology Technician at ZSL’s Institute of Zoology, blogs about how ZSL and other partners are helping to reintroduce and conserve the hazel dormouse.

A sleepy common dormouse in quarantine at ZSL
A sleepy common dormouse in quarantine at ZSL

The common or hazel dormouse (Muscardinus avellanarius) is not quite as common in the UK as its name might suggest. Previously found in almost every county of England and Wales, common dormice have undergone a marked decline in both range and numbers over the last century - estimates from the Joint Nature Conservation Committee indicate a 52% decline over the last 25 years and the majority of dormice are currently found only in some parts of southern England and Wales.  

Why are dormice numbers decreasing so much? Unfortunately, as with a number of other species, the way in which we use land has altered their former habitats and made many of them unusable for dormice. The impacts of changes in woodland management techniques, loss of hedgerows and habitat fragmentation has led to the common dormouse being designated a protected species in Britain.

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

In order to help conserve this species, reintroductions of captive-bred dormice have taken place across England over the last 23 years, helping to bolster remaining populations, and release dormice back into areas they historically roamed. 

Here at ZSL’s Institute of Zoology, the Disease Risk Analysis and Health Surveillance team (DRAHS), along with veterinary nurses and animal keepers at ZSL London Zoo, have been looking after captive-bred dormice in quarantine and conducting health examinations prior to their release.

The dormice stayed with us for approximately 10 weeks, during which time we screened them for ‘novel’ parasites that dormice may have picked up in captivity, but they are not usually exposed to in the wild. This disease risk management is essential for a successful reintroduction, trying to make sure that the dormice were not released with pathogens that could cause issues for either the dormice themselves or other wildlife at the reintroduction site.

During their quarantine period, the dormice were microchipped, so that they could be easily identified after their release, and their weights and condition were continually monitored to ensure they were in the best possible shape for reintroduction.

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

Working in partnership with People’s Trust for Endangered Species (PTES) and Natural England, on Thursday 23rd June 2016 we released our 19 dormice, along with those kept in quarantine at Paignton Zoo, into a managed woodland in the Yorkshire Dales National Park. The dormice were matched up to make breeding pairs, and the hope is that over the coming years they will establish a viable and lasting population in a place where dormice were last recorded over 100 years ago.

For the first couple of weeks of the release, they will stay in their ‘soft-release’ cages, along with plenty of food and water to keep them going, and will be monitored daily to check that they are adapting to their new habitat. Once everyone is satisfied that they are doing well, the doors will be opened and the dormice allowed to roam free around their new wild homes. PTES and the Yorkshire Dales National Park will continue to improve the habitat in the surrounding areas, in particular focussing on hedgerows, aiming to connect this reintroduced population with a similar released population a few miles away.

Reintroduction programmes such as this are vitally important for the continued conservation of a number of different species, but must be carried out in a responsible and controlled manner. The DRAHS project aims to minimise the risk of disease to these reintroductions, and monitors the health of wild animal populations at the reintroduction sites. 

Learn more about the DRAHS project

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