Kathryn Mach, a planning ecologist with Swansea Council, gave a fascinating talk about how we can keep a lookout for dormice at a Swansea Local Nature Partnership meeting in December 2024. Kathryn has kindly transformed her talk into an article for our Hwb Nature blog.
Dormouse ecology
The hazel dormouse (Muscardinus avellenarius), or ‘pathew’ in Welsh, is a much-loved part of our natural heritage as well as our cultural heritage, known for featuring as a sleepy member of the Mad Hatter’s tea party in Lewis Carroll’s Alice in Wonderland. Their name ‘dormouse’ likely originates from the Latin word meaning ‘sleep,’ which accurately describes their behaviour. Being one of only three mammals in the UK that truly hibernate (the others being bats and hedgehogs), the dormouse can spend more than half of the year asleep! Being nocturnal, they also sleep for much of the day, which perhaps also earned them their namesake.
…the dormouse can spend more than half of the year asleep!
The nocturnal lifestyle of dormice is the reason for their large black eyes, to allow them to see in the dark. They also differ from wood mice and other mice by having golden fur including a furry tail. They are found in a wide variety of habitats, such as deciduous and coniferous woodlands, scrub, hedgerows and even gardens! They feed on different foods throughout the year, starting with catkins and flowers in the spring, moving onto insects and berries in the summer and then nuts and seeds in the autumn. They fatten up from a weight of around 10-20g to 30-40g before they hibernate over the winter, as they will lose about 30% of their body weight during this time.
Dormice are known as arboreal animals, meaning that they live in trees. During the spring and summer, they construct nests within bramble and other scrub or up in the trees. The nests are usually distinct from those of other mice, and a textbook dormouse nest consists of a neatly woven sphere of material such as grass, reeds, honeysuckle bark or bluebell stems, surrounded by fresh green leaves. The nest materials will vary depending on what’s available in their local area. As with any wild animal they don’t read the textbooks so nests aren’t always perfect, and it can sometimes be difficult to determine if a nest has been made by a dormouse! In the winter dormice go to ground and make a smaller, more tightly woven nest that is usually found underneath some leaf litter. They will then spend most of the winter hibernating (depending on the weather conditions) from around November to April.
Dormouse Conservation
The hazel dormouse is found across most of mainland Europe and was historically present throughout England and Wales. However, it is now generally only present in the south of England and has a patchy distribution across much of Wales, including in Swansea, where only a handful of records exist. The State of Britain’s Dormice 2023 reported that in just the 22 years between 2000 and 2022, the dormouse population fell by 70%. It is suggested that the population should now be classed as ‘Endangered.’
Hazel dormice are protected in the UK by national and international legislation and are a European Protected Species. This means that it is illegal to kill, capture or disturb a dormouse, or to damage or destroy its breeding site or resting place. The dormouse is listed on Section 7 of the Environment (Wales) Act 2016, as a species of principle importance for the purpose of maintaining and enhancing biodiversity in relation to Wales.
The ‘State of Britain’s Dormice 2023’ reported that in just the 22 years between 2000 and 2022, the dormouse population fell by 70%.
Despite the protection afforded to dormice, they have clearly suffered huge population declines. The main threat to dormice is habitat loss and fragmentation. The loss of ancient woodlands and hedgerows means populations of dormice are either lost altogether or become isolated from one another, and so lose genetic diversity and become more vulnerable to extinction. Inappropriate management of their remaining habitats is also a potential threat. As is the case for much of our native wildlife, dormice are facing an ever-increasing pressure from climate change. Warm winters interfere with their usual hibernation patterns and cold springs and wet summers may impact on their ability to find food and breed successfully.
Dormouse Surveys
So how do we find dormice? Traditionally there are two ways to keep a lookout for dormice. The first is to look for the nests that they build, by using nest tubes and nest boxes. These are installed in trees and shrubs and give a safe space for dormice to make a nest. This is only undertaken by licensed surveyors as there is a chance that dormice will be encountered during the surveys. The other method is to look for nuts that dormice have nibbled.
Nut hunts are the easiest survey method to keep a lookout for dormice, and anybody can do it. They can be undertaken at any time of year and involve walking around an area where hazel trees are present and collecting nut shells from the ground. A magnifying glass or hand lens can then be used to identify the small mammal that might have opened them. Nuts opened by dormice have a characteristically smooth inner rim, with toothmarks on the surface of the nut at an approximately 45-degree angle. If you can imagine it, they use their mouth a bit like a tin can opener to get the nut out of the shell! Wood mice and voles use their teeth to scratch over the surface of the nut and therefore leave tooth marks on the inner rim of the hole. Squirrels crack the nuts open, shattering the shells in half. Whilst out searching for nuts, it is worth keeping an eye out for nests in hedgerows and scrub. Whilst the majority are likely to be bird nests, you may be lucky enough to find a dormouse nest. It is very important not to touch or disturb the nest in any way, but you may be able to carefully take a photograph for identification purposes.
It is also very important to share the results of any surveys with the local records centre – South East Wales Biodiversity Records Centre (SEWBReC). Records can also be entered into the National Dormouse Database. This helps to inform land management decisions and actions by nature conservation organisations, the local council, landowners and others, and most importantly will help with the conservation of dormice. The more we know about where they live, the more we can do to help improve the habitats for them.
How can I help?
Go on a nut hunt – an easy and reliable way of looking out for dormice. And don’t forget to submit any results.
If you own or manage land that may support dormice, or know somebody who does, consider management techniques that are sensitive to dormice, for example only cutting hedgerows every 3 years or so, and by avoiding cutting vegetation until the winter when most of the fruits and berries have gone.
Become a volunteer with a local wildlife group or with Swansea council. The Nature Recovery Team and Gower National Landscape Team at Swansea Council host regular conservation task days at Bishop’s Wood Nature Reserve in Caswell, as well as tree, bulb and wildflower planting across the county, and a range of of surveys such as bat walks, swift surveys, moth trapping and dormouse surveys.
Follow our Facebook pages: https://www.facebook.com/WildAboutSwansea/ and https://www.facebook.com/gowernationallandscape/ or check out our website: https://www.swansea.gov.uk/natureeventsandvolunteering
For more information about dormice (and help with identifying nuts or nests) please contact Kathryn: kathryn.mach@swansea.gov.uk
For more information about volunteering or nature conservation events with Swansea Council please contact Evie: evelyn.gruchala@swansea.gov.uk
Useful Links:
People’s Trust for Endangered Species: https://ptes.org/campaigns/dormice/
Dormouse Nut Hunt: https://ptes.org/campaigns/dormice/surveying-and-monitoring-hazel-dormice/dormouse-nut-hunt/
South East Wales Biodiversity Records Centre: https://www.sewbrec.org.uk/
National Dormouse Database: https://surveydata.ptes.org/dormouse-database
Managing Small Woodlands for Dormice: https://ptes.org/wp-content/uploads/2014/06/managing-woodlands-for-dormice-final.pdf
The Dormouse Conservation Handbook: https://ptes.org/wp-content/uploads/2014/06/Dormouse-Conservation-Handbook.pdf
The State of Britain’s Dormice: https://ptes.org/wp-content/uploads/2023/11/State-of-Britains-Dormice-2023.pdf Natural Resources Wales: https://naturalresources.wales/permits-and-permissions/species-licensing/list-of-protected-species/dormouse-licensing/
Kathryn Mach
Swansea Council
All images: Kathryn Mach
This is a great project and I am happy that the National Trust are supporting it by surveying one of our sites this year. We are ever hopeful in finding evidence of these important (and let’s admit, rather cute!) native mammals.