Captive breeding the hazel dormouse for reintroduction

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Logo: Wildwood Trust

By Hazel Ryan, Senior Conservation Officer at the Wildwood Trust

Hazel Ryan weighing a dormouse
Hazel weighing a dormouse in a captive breeding enclosure (Cathleen Cox, Wildwood Trust volunteer)

I am the Senior Conservation Officer for the Wildwood Trust, a British wildlife conservation charity working to conserve native species, restore habitats and raise awareness of our native wildlife. Our two wildlife parks in Kent and Devon are home to more than 200 animals including some species that became extinct in the UK.

My role involves management of our small mammal captive breeding programmes and providing training in handling, survey and identification skills for a range of mammal species for both professional ecologists and amateur naturalists.

I was fascinated by nature from a young age but became particularly interested in mammals whilst studying for a BSc in ecology at Royal Holloway and Bedford New College, University of London. My lecturer, Dr Pat Morris was a leading researcher on dormice in the late 1980s, when little was known about them. He took his keenest students on day trips to Somerset, crammed into his estate car, to see hazel dormouse at the very first UK nest box monitoring site, with stop offs to see otter spraint and bat hibernation sites along the way.

My first jobs after university were as countryside rangers for the London Boroughs of Bexley and Bromley. There I learnt about habitat management of nature reserves, monitoring of the species on site and raising public awareness, all skills that have proved useful in my current job. When we discovered a population of dormice in our country park, the only one known within Greater London at the time, I jumped at the chance to obtain a dormouse handling licence and set up a nest box scheme for the National Dormouse Monitoring Programme (NDMP).

I volunteered with Kent Mammal Group and Kent Bat Group, helping with bat hibernation counts and small mammal surveys. It was through the chair of Kent Mammal Group, also a trustee of Wildwood, that I heard about the new position of Water Vole Keeper to manage Wildwood’s expanding water vole captive breeding programme. My role at Wildwood soon grew to include the breeding of harvest mice, water shrews and dormice then I became Conservation Officer.

A sleeping dormouse in a gloved hand during a health check
A torpid dormice during a post hibernation health check (Hazel Ryan, Wildwood Trust)

The hazel dormouse has declined by half since 2000 in the UK, due to habitat loss, fragmentation and degradation as well as climate change. The species is a bioindicator of good habitat and a flagship species. The national reintroduction programme, co-ordinated by the Peoples Trust for Endangered Species (PTES), aims to return dormice to areas where they have become extinct.

The Common Dormouse Captive Breeders Group co-ordinates breeding of dormice for reintroduction. Members include a number of institutions who breed or hold dormice in addition to Natural England, PTES who manage the reintroductions and ZSL London and Paignton Zoo who health screen the dormice before release. Wildwood, as the largest breeder, manages the national dormouse studbook and decides which dormice will be used for breeding and which will be released.

A dormouse breeding enclosure at Wildwood
A dormouse captive breeding enclosure at Wildwood (Wildwood Trust)

There are many challenges to breeding dormice to order as we don’t know at the start of the year which pairs will breed or how many they will produce. Our breeding stock is often sourced from animals that come into rescue centres due to human disturbance (e.g. digging up hibernation nests or damaging a nest whilst clipping a hedge) or are brought in by cats. We don’t always know the age of these animals and they sometimes don’t appear to like the mate that we have selected for them. As k-strategists, dormice produce only 1-2 litters of 4-5 young per year. We also need to maximise genetic diversity within the reintroduced population which means breeding from as many different unrelated bloodlines as possible.

We house the dormice in as natural conditions as possible, in large enclosures in a woodland setting with native plants for climbing and nest material and native fruits and flowers to feed on. My knowledge of how dormice behave in the wild, through volunteering for the NDMP and attending numerous conferences over the years, has enabled me to ‘think like a dormouse’ to ensure we provide the conditions needed during each stage of their annual cycle from emergence in spring to winter hibernation. My previous experiences of small mammal trapping and keeping pet rodents as a child helped me to develop good handling skills which are essential for regular monitoring of dormouse health and breeding success.

Attention to detail is important too. Keeping records of behaviour, food consumption and activity at different times of the year really helps us to improve our animal husbandry practices. I am currently collating our observations and experiences to produce a national dormouse husbandry manual to help other breeders.   

This year I also began to analyse the 1400 records on the national dormouse studbook and presented my initial findings at the 11th International Dormouse conference in Bulgaria. It was great to exchange knowledge with like-minded people from across the world.

A captive bred dormouse climbing on a branch
A captive bred dormouse exploring its enclosure (Dave Butcher, Wildwood Trust)

There are some difficult moments to the job. I recently had to make the decision for an elderly dormouse to be euthanised due to illness. He was born at Wildwood and used frequently on our training courses due to his unusually white tail. As dormice are such long lived animals (5 years in the wild but 9 years in captivity) it is easy to become attached to them. We also lost some dormice in a flash flood a few winters ago and it was heart-breaking to have to break open their submerged hibernation nests to find out which ones had survived. I have also hand raised a number of orphaned dormouse pups. This can be stressful and time consuming but rewarding when they survive to adulthood, and in one case live for over 9 years!

Although I see dormice nearly every day during their active season, I never tire of that ‘Aaah’ moment when I look into their big round black eyes.   

If you would like to find out more about Wildwood or our conservation training courses please see:


First published in CJS Focus on Working with Wildlife in association with The Wildlife Trusts on 17 October 2022. Read the full issue here

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Posted On: 23/09/2022

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