Chester Zoo uncovers the secrets of the Hazel dormouse

Chester Zoo has uncovered some amazing new habits of the hazel dormouse after researching them for the past decade. During the study they found that females can be quite promiscuous.

Working with staff from Natural Resources Wales (NRW), local Wildlife Trusts, Denbighshire County Council and volunteers the zoo conducted the largest and longest running study of its kind in the UK.dormouseOne of the major findings was that dormice can have a number of offspring which are sired by different males in the same litter. This was discovered by taking hair samples from the Dormice and using DNA analysis techniques.

The biodiversity officer for Chester Zoo, Sarah Bird said, “Our study has shed new light on the ecology of our dormice and highlighted factors which are important for their survival in the UK. Promiscuity in females had never been recorded before; and it will increase genetic diversity within litters, helping population survival.”

It was also found that the female dormice will sometimes breed twice in the same year with some breeding before they are a year old. While some dormice on continental Europe have displayed these behaviours it is rare in the UK. Breeding before they are a year old has actually never been recorded in the UK.

These behaviours are important to the survival of this species as Bird explained, “It is likely that those years when females breed twice, and the young of the year also breed, is when populations can really increase. These behaviours are likely to be critical for healthy sustainable dormouse populations in the UK.”

Bird explained how the research has been carried out, “Our vets and conservation team and project partners have been able to visit the site four times each year for the last 10 years. Using our veterinary expertise, we’ve marked 920 dormice with tiny microchips in that time. This has enabled us to build up a huge amount of really important and unique data. We now know a huge amount about these dormice now – including how long they live, how their weight fluctuates throughout the year and how many survive winter hibernation.”


As they are protected under European law the UK must monitor the dormice. By gaining this information on habitat use, life expectancy and population changes they can deliver more effective dormouse conservation.

Bird said, “The hazel dormouse is a protected species in Europe and they’re super, charismatic little animals.”

“Our survey site in North Wales is on the very north western edge of their European range and, from the very start, we’ve been surprised by how many hazel dormice are there.”

“That’s why it’s a very important project and a very important site for study – to understand why this woodland is so good for dormice.”

In 2005 there were 45,000 dormice throughout the UK but populations had been declining since at least the 1990s. There are experts that believe the downward trend has been going for 100 years. Recent evidence suggests that potentially the decline is slowing.


As the local manager for Natural Resources Wales, Mike Whitley explained though the study site at Bontuchel is one of the healthiest, “We have one of the healthiest populations of dormice in the UK here at Bontuchel.”

“The coppice management works we carry out each year creates the just the right habitat conditions for the dormice to flourish while also making this woodland a really great place for people to visit,” he added.

Bird backed this up saying, “It is clear that habitat management by Natural Resources Wales (NRW) is making a big difference. Leaving woodland unmanaged is not good for dormice.”

Hazel dormice are named for the hazel nuts they need feed on and the French word ‘dormir’ which means ‘to sleep.’ This is a suitable name as they sleep for two thirds of their life.

They are the only dormouse species that are native to the UK.


Photo Credits: Chester Zoo

By Cale Russell is a testament to Cale’s commitment to the education of people around the world on the topic of animals and conservation, through the sharing of topical and newsworthy information.

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