30 years of putting hazel dormice back where they belong

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Logo: People's Trust for Endangered Species

By Ian White, Dormouse & Training Officer, People’s Trust for Endangered Species

A mother dormouse with her babies tucked into the corner of a nest box
Dormouse mother and juveniles in a nest box (Selena Bone)

Hazel dormice are one of Britain’s most enigmatic species, but few people ever actually see one. They are small, golden-coated nocturnal rodents that live in the tree and shrub canopy when they are active between late April and late October, and over winter they hibernate in tightly woven nests on the ground. Despite once being a common feature of our woodlands, the chance of seeing a dormouse is diminishing as the population has declined by over 50% since 2000 and dormice have been lost from 17 English counties.

To help combat this decline, a reintroduction programme began in 1993 as part of Natural England’s Species Recovery Programme. Over the past 30 years People’s Trust for Endangered Species (PTES) and partners have released a total of 1,078 dormice to 25 sites in 13 counties. We are thrilled that these reintroductions have been successful, with many populations growing naturally each year. Each shows that with care and the correct woodland management practices, we can establish dormice populations in areas where they no longer naturally exist.

The reintroduction programme is led by PTES and has changed over its 30-year history. In the early days we used both captive bred and wild dormice and we just did a single reintroduction in an area per year. Now, the Common Dormouse Captive Breeders Group (CDCBG) breeds dormice specially for the programme, so most years the vast majority of dormice released are captive bred. One of the key members of the CDCBG, Wildwood Trust, manages and maintains a Dormouse Studbook so that we know the source of each animal and how each is related to each other. This ensures that the gene pool of each reintroduced population remains as wide as possible. All dormice go through an extensive quarantine programme at ZSL in London and Paignton Zoo in Devon before they are released, to ensure that they are fit for release.

Vet holding a stethascope up to a dormouse to check their heartbeat
A dormouse having their heart and lung health checked by a ZSL wildlife vet during their quarantine at London Zoo (ZSL)

One of the challenges of the reintroduction programme is to find suitable sites to release them into each year. We need a wood that is both currently suitable for dormice and will remain so for the foreseeable future. Dormice are a species of successional scrub (the shrubby growth that regenerates when areas of woodland are cut) and so a suitable wood requires a commitment to its ongoing management by the landowner. Larger organisations such as the National Trust (landowner for this year’s reintroduction at Calke Abbey in Derbyshire), Natural England, Wildlife Trusts and national parks are more likely to be able to offer the required long-term commitment to the woodland management, which is why PTES often partners with such organisations. They also tend to have a larger base of enthusiastic volunteers, who are vital to the ongoing success of a dormouse reintroduction.

Where we used to do just one reintroduction in a designated area, we now aim to do at least two, ideally about 3-5km apart. We then work with local organisations, volunteers, and landowners to create a suitable corridor between the reintroduction sites (usually by improving the hedge network) to enable the dormice from both sites to occupy and use the wider landscape. Our hope is that the two populations will eventually create a self-sustaining local metapopulation that should be more robust and better able to survive minor disasters such as localised habitat destruction or a poor breeding year.

Hazel dormouse balancing on a bramble amongst the leaves
Hazel Dormouse peaking out of leaves on a branch (Claire Pengelly)

This approach has proved to be very successful in Nottinghamshire, North Yorkshire, Warwickshire, and Lancashire to date. In Nottinghamshire, three dormouse reintroductions led to the formation of a local dormouse group who now work with the local Wildlife Trust to manage the woodlands and to restore hedgerows in the local area. The dormice here have moved from one of the woodlands we reintroduced them into and been recorded in the neighbouring wood. Although the 160m distance travelled might seem small to us, it’s a big leap for small dormice!

In the 1900s dormice were recorded in Wensleydale, North Yorkshire, but the population died out. In 2008 dormice were reintroduced into the area and a further reintroduction took place in 2016 to boost the existing population. The latter was in a woodland 4 km away from the 2008 site, and a 3-year project, part funded by PTES, improved the connectivity between the two woodlands (by planting and improving hedgerows and improving woodland management in some of the local woods) to allow dormice to disperse beyond the sites where we released them.

This year, the reintroduction is taking place in a large, secluded woodland on the Calke Abbey estate in Derbyshire, which is cared for by the National Trust. The National Trust’s countryside team and a group of volunteers will be responsible for the ongoing care of the dormice and long-term management of the woodland after the reintroduction has taken place. The woodland is in the heart of the National Forest where over 30 million trees have been planted over the past 30 years creating lots of potential sites for future reintroductions.

Man in a hospital mask and latex gloves holding up a dormouse that is about to be released
Ian White, PTES' Dormouse Training Officer holding one of the hazel dormice being released into the National Forest (National Trust Images & James Beck)

While the majority of this year’s dormice will be released into the National Forest, we also plan to release a smaller number into a woodland in Cambridgeshire, at the site of the very first dormouse reintroduction back in 1993. Back then, 49 dormice were released and 30 years later descendants of those released animals still survive in the woodland, which is fantastic. But because there are no other local populations, a supplementary number of dormice is now needed to increase the gene pool.

The ongoing success of PTES’ annual dormouse reintroductions is the result of a unique partnership and many passionate volunteers who together work tirelessly to help us bring dormice back from the brink and ensure their ongoing survival. Well-managed woodlands and hedgerows are key to restoring dormouse populations across the UK, so releasing dormice into such habitats is crucial for the species’ long-term recovery. The National Forest is home to a huge array of woodlands suitable for dormice, so we hope that this is the first of many reintroductions to take place in this part of the country.

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Posted On: 14/06/2023

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