Press release: Climate change is exacerbating hazel dormouse decline, new research confirms

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New research has confirmed that increased precipitation and fluctuating winter temperatures, as well as density dependence all negatively affects hazel dormouse populations. Worryingly, changing weather patterns – which are increasing – appear to exacerbate populations that are already struggling. The study warns that without mitigating these factors, dormice could disappear from our woodlands altogether.

The research was led by Dr Fraser Combe, former PhD Student at Manchester Metropolitan University, and supported by wildlife charity People’s Trust for Endangered Species which spearheads the UK’s hazel dormouse conservation work. It has been published in leading journal Animal Conservation.

A native hazel dormouse in a woodland. Credit Clare Pengelly. [High-res image available]

By studying long-term data gathered on 4,000 animals from four UK populations (via PTES’ National Dormouse Monitoring Programme) and one in Europe, Fraser, PhD supervisor Dr Edwin Harris and colleagues were able to investigate exactly what impact changing local weather patterns has on population growth rates, and how these interact with other factors contributing to the species’ decline.

Lead author Dr Fraser Combe explains: “Our results showed that increased rainfall, fluctuating winter temperatures (rather than stable cold temperatures) and density dependence are all contributing to the species’ decline. As population density increases, a population can reach carrying capacity, resulting in more individuals competing for food and nesting sites. In areas where food and shelter are plentiful this is less of an issue, but lack of sympathetic woodland and hedgerow management leads to less diverse habitat. This, combined with increased fragmentation of habitat patches, means that the number of dormice those areas can support is lower. The plights of these populations is exacerbated by a changing climate.”

“When a population is at capacity, a bad winter or a year of fluctuating and unusual weather has a stronger and more negative effect on dormouse populations than during a stable winter. We also found that although warmer and wetter weather impacts dormice of all ages, there were subtle differences between adults and juveniles.”

The research showed that in adult dormice, both over winter survival and fecundity (the ability to breed successfully) were negatively impacted by increased average temperatures and higher rainfall, especially when these patterns of warm, wet weather were interspersed with cold periods. It’s not uncommon for hibernators to wake up intermittently, but frequent waking depletes the adults’ energy reserves by the time they wake in spring, thereby hampering their breeding capacity.

Juveniles were impacted before hibernation and over winter. If juvenile dormice don’t build up enough fat reserves before winter their chance of surviving hibernation is slim. That, combined with waking up early or more frequently and being forced to be active when they should be asleep and when there’s less food around, has serious consequences too.

But the study did offer some cause for optimism: conservationists can help mitigate against these negative effects, giving dormice a fighting chance. Measures such as coppicing, improving hedgerow quality and connectivity between suitable habitats, planting diverse tree species that fruit and flower in varying seasons, and host an abundance of invertebrate species, and creating plenty of scrubby edge habitat can provide more nesting sites and ensure year-round food availability. This will help improve resilience through periods of unpredictable weather pattens, and hopefully enable dormice to better survive winter and successfully breed come spring and summer.

Torpid dormouse in nest. Credit Hattie Spray

Nida Al-Fulaij, Conservation Research Manager, People’s Trust for Endangered Species explains: “Hazel dormouse populations have fallen by a staggering 51% since 2000 [PTES’ State of Britain’s Dormice 2019 report], and they’re listed as vulnerable to extinction on the Red List for Britain’s Mammals 2020. Understanding what is driving this decline is critical, so that we can put measures in place to prevent further decline, restore populations to stable levels and ultimately stop dormice from disappearing from our woodlands and hedgerows.”

“Fraser’s study also highlights how vital long-term data collection is. Thanks to the National Dormouse Monitoring Programme (NDMP) which PTES has been successfully running since 1993, we’re able to gain insights into how different populations are faring year on year and implement targeted conservation measures to populations that need the most help. Through our ongoing work we’re starting to make a difference, but we desperately need more better-managed woodland and hedgerow habitats across the country in order for dormice to really become commonplace again.”

With the help of thousands of dedicated volunteers and like-minded conservation organisations, ecologists, researchers and government agencies, PTES has worked tirelessly over the past 30 years to try and combat the decline in hazel dormouse numbers. In addition to running the NDMP, the charity also leads the annual reintroduction programme (which celebrates its 30th anniversary this year), manages the National Dormouse Database, funds vital research like Fraser’s, and provides bespoke training for woodland owners and land managers to ensure that woodlands and hedgerows are appropriately managed for dormice.

Combatting such a dramatic decline will take time, but it is hoped that armed with the latest research and data, PTES will eventually bring dormice back from the brink.

To read the full paper, visit: and to find out more about PTES’ dormouse conservation work, visit:  

Header image credit John Webley

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For high res images, interview requests or further information, please contact Adela Cragg:

T: 07532 685 614


Notes to Editors

Available for interview

  • Dr Fraser Combe, lead author
  • Nida Al-Fulaij, Conservation Research Manager, People’s Trust for Endangered Species
  • Ian White, Dormouse & Training Officer, People’s Trust for Endangered Species

About PTES

  • PTES, a UK conservation charity created in 1977, is ensuring a future for endangered species throughout the world. We protect some of our most threatened wildlife species and habitats, and provide practical conservation support through research, grant-aid, educational programmes, wildlife surveys, publications and public events.
  • PTES’ current priority species and habitats include hazel dormice, hedgehogs, water voles, noble chafers, stag beetles, traditional orchards, native woodlands, wood pasture and parkland and hedgerows.
  • PTES has Species Champions for two of its priority species: for hedgehogs The Rt Hon Chris Grayling, MP for Epsom & Ewell and for water voles The Rt Hon Hilary Benn, MP for Leeds Central and Chair of the Brexit Select Committee.
  • Visit and follow PTES on Facebook, Twitter, Instagram, YouTube & LinkedIn.

About the Manchester Metropolitan University 

  • Manchester Metropolitan University is one of the top modern universities for research quality, with 30% of their overall research being rated as world leading.
  • 100% of their environmental science research is rated as world-leading or internationally excellent for impact, and the University’s Ecology and Environment Research Centre is ranked fifth nationally for impact. 
  • Research brings together a multidisciplinary group of academics with expertise in a range of subjects including species biology, conservation, environmental change, and sustainability. 
  • The institution also has strong relationships with academic groups around the world. The applied nature of much of their research ensures strong industrial support and collaboration.

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