The Dormouse Blog

Believe it or not, there is an animal in Shropshire that spends more of its time sleeping than I do. During the course of one year, they spend up to 9 months of their time fast asleep or resting. Which is how the Hazel Dormouse Muscardinus avellanarius got its name. The name “dormouse” derives from the French word for sleep, they are literally called “sleepy mouse”.

Despite having the word “mouse” in the name, dormice are not actually related to mice at all, but their mouse-like appearance make it clear why they were mistakenly grouped together with mice. Across Europe, there are other species of dormouse: the edible dormouse, forest dormouse and garden dormouse, along with the hazel, which is the only native species found in the UK. One of the key behavioral differences between dormice and our real mice is that unlike other mice, dormice hibernate through the winter months. They are the only UK rodent that sleeps through times of colder weather.

As autumn sets in, dormice become very active. Having spent much of their summertime resting, sleeping and breeding, they then go onto spend most their waking hours eating the abundant nuts and berries supplied by hazel trees, beeches, brambles and hawthorns. Their aim: try to eat so much that they double their own body weight from around 20g to 40g. As much fun as that may seem, in the case of dormice, it is an essential survival mechanism. In order to survive a full hibernation for a few months, they must have developed enough body fat to keep their body functioning and able to become active again in spring. Sadly, without gaining that weight, sleepy mice won’t hibernation and it is estimated that half of dormice die during their winter slumber.

These small, ginger-furred mammals are around 15cm in length from nose to tail tip. Their big, glossy black eyes have evolved to allow them to forage for food in pitch darkness and long whiskers allow them to feel their way around safely around tree tops and mid-canopy during the night. This nocturnal behaviour makes dormice almost impossible to spot. Their numbers have also plummeted by 50% over the last two decades, as landscapes have been altered and woodland management no longer focuses on widespread coppicing. A reduction in the amount of hedgerows has also had an impact and many dormice will have been accidentally wiped out as hedgerow management was industrialized. Traditional hedgerow management involved cutting back hedges with hand tools and many workers would discover dormouse nests, which would generally be saved from destruction. Hedge-cutting by huge machines is much more destructive and other small mammals like bank voles and harvest mice are also likely to be impacted too, as well as a range of hedgerow-dwelling birds.

Dormice are now listed as vulnerable in the UK and at the current rate of decline, they could be lost completely within the next 20 years. Fortunately, there are national efforts to create more suitable habitat for dormice and to reintroduce traditional coppicing techniques, which creates ideal conditions for dormice to build a winter nest in. There have been reintroduction projects to restored woodlands in other parts of the Midlands, where dormice had already disappeared. In Shropshire, we are fortunate enough to have dormouse populations throughout the Shropshire Hills AONB and woodlands along the Welsh border. They have been recorded by nest box monitoring schemes at 4 Shropshire Wildlife Trust nature reserves and those reserves are now managed for the benefit of the small rodents living in them.

Nest box schemes have made it much more straightforward to find dormice. The boxes are similar to bird boxes, but have the entrance hole on their rear side, facing the tree trunk. They offer dormice somewhere to create safe summer breeding nests where there are limited natural options. We have installed nest boxes across those nature reserves where dormice have been recorded, with help from Shropshire Mammal Group and Shropshire Dormouse Group. The boxes are checked regularly throughout the summer, right through to October for signs of use by dormice. Of course, the target species aren’t the only wildlife to make the nest boxes their home. I have regularly encountered wood mice, yellow-necked mice, common shrews, slugs and event wasps during nest box checks! Because it involves a protected species, dormouse monitoring requires a license from Natural England, for which a few months of training is required. So, it might be very tempting to have a sneaky look inside a nestbox as you wander around a woodland, but it could land you a fine of up to £5000 (let along cause unnecessary disturbance).

Nibbled nuts — Left: bank vole, centre: wood mouse, right: dormouse.

Another way to determine whether there are dormice present in a woodland (usually before installing nest boxes) is to look for the evidence they tend to leave around. In hazel woodland, we usually look for nibbled hazel nuts with the tell-tale perfectly smooth, round hole that dormice create in the shells to reach the protein-rich inner contents. Other small mammals always create rough holes, jays and woodpeckers smash the nuts apart on rocks and hardwood, while grey squirrels crack the nutshell in two. Once a few dormouse-nibbled nuts have been found, it is then worth thinking about installing nest boxes to monitor, which would give a clearer picture of the population size and breeding rates.

For such a small mammal, dormice live in very low density, with just 3 or 4 sharing the same hectare of woodland together. So, with that in mind, it is quite clear what needs to be done to stop them disappearing and to help them thrive once more: more of the trees and shrubs that they depend on needs to be planted. And large areas of uncut bramble need to be left untouched unless it has been thoroughly checked for signs of dormice nests. Like so much of our local wildlife, dormice can only survive if they have the key requirements of survival: a habitat that provides safe cover in abundance, plants that provide a supply of food from spring until the next winter and plenty of safe places to make nests; for rearing young in the summer and for hibernation in the winter.