Hazel dormouse

Hazel dormouse

Dormouse - Brett Lewis

Dormice are thriving in Suffolk Wildlife Trust reserves, including Bradfield Woods and Arger Fen.

To ensure a sustainable population and re-colonisation of nearby woods and hedges it is essential that we restore and strengthen links between woodland SSSIs.

In order to help dormice, it's important to know where they are. By recording any sightings or evidence of these legally protected mammals, from nests to nutshells, you can help keep Suffolk a dormouse stronghold.


Dormice can easily be recognised by their thick furry tail, bright golden-brown colour and large black eyes. They are about 70mm long with a tail of similar length. Their weight varies from 17g (about the weight of two £1 coins) up to 40g at the start of hibernation. Juveniles are about half adult weight.

As the dormouse is rare, strictly nocturnal and usually forages for food often high in the tree tops or in hazel thickets, rarely coming to the ground, you’re not likely to be lucky enough to see one. The best indication of its presence is characteristically chewed hazelnuts on the woodland floor.

The dormouse opens the nut by making a small round neat hole on one side and leaves tooth marks on the nut surface but not on the cut edge.

Where do they live?

They are found in deciduous woodland and thick hedgerows mainly in southern counties from Cornwall to Kent northwards to Herefordshire and Northamptonshire. There are scattered records north of here including the Lake District and Northumberland. There are also scattered records for parts of Wales but they are not found in Scotland.

In Suffolk, most of the records come from the south of the county, within the Stour Valley, but we know their historical range extended further north, nearly to Bury St Edmunds.

Early results from our Suffolk dormouse survey in autumn 2013 found dormice at Arger Fen & Spouse's Vale, Groton Wood and close to Bull's Wood.  We also know dormice are thriving at Bradfield Woods where the Trust has worked with local landowners to create a new tree belt and hedge to allow dormice to re-colonise and spread.

What do they eat?

They feed on flowers, pollen, fruit, insects and ripe nuts. These are available in turn as the summer progresses so the dormouse needs a habitat containing a good variety of shrubs and tree species to ensure a continuous supply of food. Hazel, honeysuckle, bramble and oak are particularly important food sources.

What do they do during the day?

They sleep during the day in a nest, often in a hollow tree branch or dense shrubs such as holly or honeysuckle. Dormice construct their own nests from shredded honeysuckle bark woven into a ball, which they often surround with layers of leaves. These nests may also be out in the open, close to the ground, typically in low bramble bushes. They also take readily to nest boxes designed specially for them.

The old English name for the animal is ‘the sleeper’ and they usually hibernate from the first frosts, often in October and November and are not active again until April or May.

The hibernation nest is built on or near the ground and the animal curls into a ball and goes to sleep. Their body temperature drops to that of the surroundings and the heart and breathing rate are often reduced by 90% or more.

How many young do they produce?

Dormice have one or occasionally two litters a year, usually of about four young. The animal is very sensitive to the weather and in years when food is scarce and when bad weather has prolonged hibernation or restricted the amount of time it can spend feeding during the night, most litters may not be produced until August or September. In very bad years dormice may not produce young until October and, in those cases, it is unlikely that the young dormice will build up sufficient fat reserves to survive the winter. The dormouse does, however, live for up to 5 years, longer than other small rodents.

Fragmentation of woodland habitat

The main cause of the major decline of the dormouse over the last 100 years is the loss and fragmentation of its woodland habitat and changes in woodland management practices. Dormice are reluctant to cross open country and so if a wood becomes isolated and too small to provide sufficient habitat for the animals needs it becomes locally extinct. Loss of ancient hedgerows is also likely to be significant.

Coppicing was once widespread. This traditional management created ideal habitat with sprawling branches to provide pathways for dormice above ground, plenty of different shrub species and not too much shade from big trees overhead. Although there is increasing interest in reviving coppice management it is important to ensure that there is a long enough rotation between coppicing (ideally 15-20 years) to provide fruiting hazel, and that the cleared areas are not too large.


Dormice are strictly protected by law and may not be collected, sold or disturbed in any way. A licence is needed (from English Nature or the Countryside Council for Wales) to inspect nest boxes used by dormice.

Helping dormice

In order to help them, we need to know where they are. One of the best ways of finding out if dormice use a wood or hedgerow is to look for hazel nut shells that they have opened to get at the nut inside. Dormice open these nuts while they are green and still on the tree, but the shells turn brown once they fall to the ground. Other animals like hazel nuts too, but quite often it’s possible to tell what has opened the nut. Birds and squirrels usually split nuts completely in half or smash the shells in pieces, but small rodents (mice, voles and dormice) gnaw neat holes in the
shell and leave characteristic marks around the edge.

In the case of dormice, these marks are quite distinctive. Looking for hazelnuts is something anyone can do and if you think you have found some nuts opened by dormice, we would love to hear from you.