The hazel dormouse (Muscardinus avellanarius) is a protected species and native to the UK. These mammals have declined significantly in the UK and there are many reasons for this but the south west still seems to be a strong hold for this species. We are very fortunate to have dormice present at some of our reservoirs and lakes in Devon and Somerset. This year, we even found a new site with dormice!

Last time I wrote a dormouse blog I was telling you the story of the new Wimbleball Lake dormice, you can read it here. Now, I shall tell you about the dormice we found at Fernworthy Reservoir, Devon. In July of 2021 I put out 20 dormouse tubes around a small part of the site at Fernworthy Reservoir, as I had found a record of dormice being present in 2004, not too far away. I checked the tubes later in 2021 and at the start of 2022 and I had found nothing except spiders, bird poo and feathers and centipedes. In September 2022, I went to look at my tubes, expecting to find the same as before, and I didn’t. Instead there was a perfectly made dormouse nest in one of the tubes!


For the first time this year we also invited volunteers to come along to Meldon Reservoir to check the 20 dormouse boxes we have there. For the last few years, I have checked this site alone as there were some tricky fences and wires to climb over, but now that has all been fixed I can now take people safely to this site too.

This year’s totals (for May and September 2022) are lower than any other year I have done and are as follows. Do note that finding a dormouse nest and no dormice is still evidence that they are using the site, it is not a bad thing. It just means that on the day I checked the boxes the animal was elsewhere.

  • Wimbleball Lake, Somerset, had 5 dormice and nests
  • Fernworthy Reservoir, Devon, had 1 dormouse nest
  • Trenchford Reservoir, Devon, had 7 dormice and nests
  • Roadford Lake, Devon, had 1 dormouse and nests
  • Meldon Reservoir, Devon, had 6 dormice and nests
  • Longham Lakes, Dorset, had no evidence of dormice


Although we have found relatively low numbers of dormice this year, natural populations of dormice (and other animals) will fluctuate from year to year depending on things like food, local weather and predation. The local distributions and how they use a site will also change and this might be down to things like food availability and disturbance. Dormice are known to live in low numbers, even in the best of habitats. The National Dormouse Monitoring Programme suggests an average of 1.75-2.5 adult dormice per hectare.

Our monitoring is allowing us to keep a good eye on what is happening with our dormice at our sites. Aside from monitoring the boxes we also make sure that any management is sensitive to dormice and last year we also did some coppicing at Roadford Lake.

Coppicing a woodland promotes the new growth of trees, allows trees to fruit (especially trees, like hazel, which don’t fruit when they get older), increases the diversity of plants on the woodland floor and creates suitable places for dormice to hibernate. These are all elements which a healthy dormouse habitat requires.

We have also been in touch with a PhD student who is looking at how dormice use habitats around our box schemes. She is using Roadford Lake as one of the study sites. Hopefully, this will shed light on how dormice are using our sites and that the number we are seeing in our boxes is not a true reflection on how many dormice are present.

We are proudly part of the National Dormouse Monitoring Programme and so all of our findings go towards understanding dormice ecology and the wider populations. We will continue to keep up our good management to ensure that this protected species continues to succeed at our sites.

I must also say a big thank you to South West Water who often fund our dormouse boxes and tubes which allow us to monitor our dormice and to find new sites.

As always, we find intruders to the dormice boxes. This year they included birds, moths, spiders, slugs, snails, pygmy shrew and toads!

If you would like to receive details of these dormice events and other wildlife surveys, please email [email protected].