Many species that are habitat specialists – organisms that rely on specific environments or food sources – are declining in what is becoming a worrying trend. One such specialist facing this threat is hazel dormice (Muscardinus avellanarius), a species intimately linked with certain woodland habitats. Dormouse populations in Britain have plummeted by a staggering 78% between 1994 and 2020 with traditional conservation efforts focused on restoring broadleaf woodlands where key species like hazel and honeysuckle provide food and shelter. Yet, despite these well-intended strategies, dormice numbers continue to fall, largely due to habitat loss and the decline of traditional woodland management practices such as coppicing.
Recent studies, however suggest dormice may not be the strict habitat specialists we once thought. Emerging research is challenging the idea that dormice are solely dependent on broadleaf woodlands. Populations have been found in scrubland and conifer plantations -habitats long deemed unsuitable for these creatures European studies also show dormice in locations such as roadside verges, high-altitude conifer plantations, and reed beds. In these unexpected environments, dormice appear to rely less on specific plant species and instead show a greater degree of opportunism, feeding on a diverse array of invertebrates and seeds.
Stable isotope analysis
To help us better understand how dormice adapt to marginal habitats, researchers have turned to stable isotope analysis. This technique allows scientists to track dietary patterns by examining carbon (δ13C) and nitrogen (δ15N) isotopes in dormouse fur, which can then be compared to isotopic signatures of local food sources. In my study, broadleaf and conifer woodland sites in North Wales were sampled and compared to learn more about how dormice adapt their diets depending on which habitat they live in.
I studied the dormouse populations at two woodlands in Wales, Clocaenog, a conifer woodland, and Bontuchel, which is a broadleaf woodland.
The fur samples that I collected in spring indicated that dormice in Clocaenog have a mixed diet whereas at Bontuchel a substantial part of the dormouse diet was made up of nuts and seeds. About 80% of the dormouse diet in the broadleaf wood was made up of beech nuts and flowers, birch seeds, and sycamore seeds.
The differences between the diets of the dormice in the two woods became even more pronounced in autumn. At Clocaenog, tree seeds made up 40% of their diet, with invertebrates making up another 39%. In contrast, the dormice at Bontuchel seem to be heavily reliant on berries, which comprise about 70% of the food they eat.
One particularly noteworthy finding from my study was the difference in niche breadth between habitats. Niche breadth refers to the range of resources or environmental conditions a species can tolerate or needs in order to survive. Dormice in broadleaf woodlands, such as Bontuchel, had larger trophic (food) niches -indicating a more varied diet – compared with those in conifer habitats. Dormice in Clocaenog had smaller trophic niches, revealing that they have a more restricted diet. Yet, despite their narrower diet, the dormouse population in Clocaenog has been stable since monitoring began in 2018, showing just how adaptable they can be in different habitats.
My findings demonstrate just how flexible dormice can be, depending on what is available. It reveals that they are able to adapt what they eat, according to what food is available locally.
Dormouse diet flexibility
The flexibility shown by the dormice in the Welsh woodlands is similar to findings from other studies in Europe, which also demonstrate that dormice can persist well beyond the edges of what we consider their preferred habitat of broadleaf woodlands.
A recent study by our colleagues in Germany, investigated the diet of dormice living in spruce and beech forests compared with a control site that had a much broader variety of shrub species. At the control site, dormice ate a range of flowers (pollen) in spring including Norway spruce, common hawthorn, willow, English oak and European beech. The dormice also fed on acorns, fungi and arthropods. During the summer months, from July onwards, their main source of food was fruits, particularly rowan and hawthorn berries. Raspberries, blackberries, and sloe were also eaten but they made up a much smaller proportion of their diet. In autumn, the dormice appeared to rely mainly on acorns and beech nuts.
In comparison, in spruce dominated forests, dormice were mainly feeding on arthropods and spruce seeds; their diet was predominantly vegetative plant material. In the beech forest, the dormouse population was mostly feeding on beech and willow shoots and pollen, supplementing their diet with beech nuts and arthropods.
Interestingly, it was apparent that the dormice relied heavily on invertebrates in autumn. Previous research has highlighted how important insects such as butterfly and moth larvae are for dormice, but this study suggests dormice consume a broader range of invertebrates, particularly when environmental pressures vary. For instance, the extreme drought of 2022 – Britain’s hottest summer on record – may have drastically reduced the amount of seeds and fruit that our trees produced, forcing dormice to eat more invertebrates than usual. If this is the case, its further evidence that dormice are more adaptable in their diets that we once thought and that, hopefully they are able to adjust to changing environmental conditions.
Rethinking conservation strategies
These new insights have important implications for dormouse conservation. If dormice can adapt to and even thrive in habitats with low plant diversity, they may be able to persist in what we consider marginal habitats, as long as they have access to enough food resources throughout the year.
For conservationists, this means that we need to think beyond restoring broadleaf woodlands that are rich in hazel and honeysuckle. Instead, our management strategies should include a wider range of habitats. Creating and maintaining a diverse mosaic of habitats, including woodland edges, clearings, and even scrubland, may be crucial for supporting dormouse populations. These efforts should ensure that we have enough large trees with abundant flowers and a variety of invertebrates, providing year-round food for dormice.
Our conservation protocols need a wider scope. Traditionally, our efforts have focused on hazel-rich sites. However, given dormice have demonstrated how flexible they are, we need to ensure that we focus both our survey and conservation efforts more broadly. Footprint tunnels which allow for quick detection, should be used across a wider variety of habitat types so we can continue to increase our understanding of what suitable dormouse habitat looks like. Only then can we hope to halt their ongoing decline. Understanding the adaptability of hazel dormice is more than just an ecological curiosity — it’s a vital clue in how we can better support this endangered species in an increasingly fragmented and changing world. By rethinking habitat specialisation, we can develop more effective conservation strategies that embrace their surprising versatility.
Written by Charlotte Armitage
Image credit: Rhys Own-Roberts, Jamie Edmonds