Dormouse discovery

Last week, I took a brilliant course on Dormouse Ecology and Surveying, organized by Sussex Wildlife Trust. I was particularly excited because the hazel dormouse is extinct in Brussels (and very rare in the rest of Belgium), so I had never had the chance to see one, let alone learn more about this charming creature. πŸ™‚

What is a hazel dormouse?

The hazel dormouse is a small (6-9 cm long) rodent. With its furry tail, large eyes and ginger colour, the hazel dormouse is easy to distinguish from other rodents. It has a large distribution in Europe, but the UK is located in the northern part of its range and numbers are low (+- 45000).

The name “dormouse” comes from the french word for sleeping, “dormir“…because they “sleep” (actually hibernate) for half of the year.
They can also enter torpor (temporary hibernation) for a few hours each day during their active period, in order to save energy. You might have seen the Youtube hit and over-cute video of a snoring dormouse. This is what torpor looks like! πŸ˜€ :Β Snoring Dormouse

Where does it live?

It is a nocturnal and arboreal mammal, loving well-connected habitats : woodland with a nice understorey, thick hedgerows, which support plenty of different food sources.
Left would be a good dormouse habitat, right…not as good. But dormouse can sometimes thrive in apparently “unsuitable” habitats like conifer plantations or gardens!

Actually, the site of the course, Tilgate Park in Crawley is not the “ideal” habitat for dormice, yet there is a nice population living there!
Thanks to its claws and prehensile, “sticky” feet, the dormouse is a good climber.
In winter, dormice don’t live in trees…they hibernate in the ground, where humidity and temperature are more stable.

What does it eat?

The hazel dormouse has a particularity : it doesn’t have a caecum, and can’t digest the cellulose contained in leaves and branches.
What the dormice eat depends on the time of the year. In spring, they will feed on flowers, nectar and pollen. In early summer, there’s a “food gap” (no more flowers, but no ripe fruits yet), so they switch to eating insects like aphids, or small caterpillars. In late summer, they need to gain weight before the winter, so they tend to eat food with a high energy content : berries, seeds and nuts, particularly hazelnuts.

How do you survey for dormice?

Being nocturnal, dormice are really difficult to survey visually, and you will probably never meet one during the day! As a consequence, ecologists have developed two easy ways to survey for dormouse : tubes and boxes.
Dormice not only build a nest for breeding, but also for resting, sleeping, etc. Naturally, they wild do it in thick hedgerows, holes in trees…so boxes and tubes can replace these structures.
Boxes look like…well, birds nest boxes, except that they are bigger, that the roof can be taken off (by sliding or lifting it), and that the hole is in the back. They are attached on trees, at a height of 1-2 meters, and can easily be removed when surveying.
Tubes are made of folded waterproof cardboard, with a sliding board of plywood. They are usually attached horizontally to a big branch. Tubes are mainly used in spring and autumn : dormice don’t seem to use them a lot for breeding, in summer, probably because they’re a bit too small!

As you can see, the typical dormice nest is made of woven bark, mainly of honeysuckle bark (Lonicera periclymenum), plus a few leaves and twigs. But dormice can also build atypical nests, like this one with a little male in here, made only of leaves. Dormice can also borrow nests made by birds early in the season (the one you see here, made of moss, with some feathers left is clearly a bird’s nest…but you also notice the typical strips of bark used by dormice!).

In one of the boxes, we actually managed to see a female with at least 4-5 babies. There are pinkish-greyish, with eyes closed, and very tiny…so they’re probably just a few days/a week old. We did not weigh the mother nor the babies, but what a great sighting!

In one of the other boxes, we disturbed a female, who was clearly pregnant. This is the safe way to handle a dormouse, you can see the bushy tail, you can also easily sex it in that position. For more information on dormice handling, check the brilliant post of a friend ecologist : Handling dormice/

After sexing and weighing, dormice must be put back into the nest box by pushing them through the hole…which can be quite difficult! That little male escaped from the hands of the surveyor, and climbed straight away into a nearby tree. Told you they are good climbers! πŸ˜‰

There is another way of surveying for dormice, which is nuts. Of course, it works onlyif there are hazelnut trees in the dormice site. Dormice tend to eat the nuts in early autumn, when they are still green, so the survey is done at that time of the year. I’m not sure I would be able to ID those for certain, I think it takes quite a lot of practice…

Squirrels and birds tend to crush hazelnuts, or make large holes in it.
Wood mouse, bank voles and dormice all make smaller holes (8-10 mm) but the shape is different between these three species.
– The bank vole leaves parallel teeth marks on the inside, but no marks on the outside of the nut.
– The wood mouse leaves parallel teeth marks on the inside, and rough marks on the outside of the nut.
– The dormouse carves a smooth hole, and the teeth marks are parallel, but at an angle to the hole.
Three nut samples for these three animals (although the difference is not very clear, because these are well dried nuts!) :

Why survey for dormice?

That’s a good question! Dormice numbers have declined dramatically in the past 100 years, and have become extinct in at least 7 counties. The biggest reason is the loss and fragmentation of their typical habitat, then come predation and bad weather as other major threats.
But why would we build boxes and tubes, pay ecologists, develop conservation programmes and manage hundreds of hectares of woodland for such a tiny and largely unknown creature?

1) It is a flagship species. If you’re not sure of what that means, check here : The dilemma of conservation/. No one can deny that, dormice are ΓΌber-cute, and can raise the awareness of people who perhaps don’t have a passion for wildlife. Whether you’re a child or an old bloke, these guys sure know how to melt your heart!

2) Dormice are good biodiversity indicators. They need a high level of biodiversity (both in plant and animal life) to settle and maintain their numbers in a particular habitat. If dormice are present, you can obviously say the site you’re looking at is biologically interesting. And if you enhance a habitat for dormice, you can be pretty certain that it will be beneficial to other groups, like birds or insects.

3) As you’ve seen on the map above, the UK are the north-western limit of the dormice distribution range. It is therefore very important to preserve UK populations and genetic diversity.

4) Dormice might only be tiny rodents found in small numbers, but they still have a role in the ecosystem! For example, the fur and whiskers can carry pollen and help to fertilize flowers.

I know there is a debate on the utility of preserving dormouse, as for pandas or tigers! I would be interested to have your thoughts on the subject πŸ˜‰
That being said, I’m on the “preserving dormouse is important because it helps preserving the habitats” side and I would love to get more involved in dormice conservation.

A cute picture, courtesy of Surrey Wildlife Trust, Β© Dave Williams:

You can even adopt a dormouse here, and contribute to conservation projects! πŸ™‚


  1. That video of the snoozing dormouse is the cutest thing I have seen in a long time! This is a great post – I haven’t managed to see young yet, as all the ones we have seen down here are very underweight and not in good enough condition to breed 😦 Poor little things. We had a male at 16 grams…

    1. Thanks! Loved your post about handling too πŸ˜‰
      They are breeding late in that site this year, not sure how these youngs will cope with winter. :/
      Hopefully the better weather now and in autumn will enable them to catch up and gain enough weight before hibernation…hopefully
      This year has really been crap for any kind of wildlife, except slugs and snails, and fungi 😦

  2. Absolutely delightful post Sophie, and a lovely series of photographs too. I particularly like the picture of the mouse running up the tree.

    I’ve never seen a dormouse, but I live in hope… especially now I’ve seen your post πŸ™‚

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