The hazel dormouse (Muscardinus avellanarius), also known as the common dormouse, is a small rodent. It is the only living species in its genus.
It is  long with a tail of . It weighs , increasing to  just before hibernation. The hazel dormouse hibernates from October to April/May. In British sources, it is normally called the dormouse rather than the hazel or common dormouse.

The hazel dormouse is native to northern Europe and Asia Minor. It is the only dormouse native to the British Isles, although the edible dormouse (Glis glis) was accidentally introduced to the British Isles and now has an established population).

The locations in the UK where the hazel dormouse can be found is shown on the National Biodivestity Network website.

Protection status 
The hazel dormouse is a European Protected Species and is protected in the UK under the Wildlife and Countryside Act.

Natural history 
The hazel dormouse is the only small mammal in Britain to have a completely furry tail. It has golden-brown fur and large black eyes. It is a nocturnal creature and spends most of its waking hours looking for food in trees. It will make long trips in tree branches instead of coming down to the ground. This is to avoid danger.

In winter (early October), the hazel dormouse will hibernate in nests beneath the leaf litter on the forest floor. When it wakes up in spring (late April or early May), it builds nests out of honeysuckle bark, fresh leaves and grasses. If the weather is cold and wet and there is not much food, it saves energy by going into torpor (a temporary hibernation). It curls up into a ball and goes to sleep. The hazel dormouse spend a large amount of its life sleeping, either hibernating in winter or in torpor in summer.

Identification signs 

Examination of hazelnuts may show a neat round hole in the shell. This shows that it has been opened by  a small rodent like the dormouse, wood mouse, or bank vole. Other animals including squirrels or jays will either split the shell completely in half or make a jagged hole in it.

If you look closer at the hole, the inner rim of the hole will have toothmarks which are at an angle to the hole (if it has been made by a dormouse).  The toothmarks are parallel with rough marks on the nut surface if a wood mouse made the hole. The bank vole leaves parallel grooves with no rough marks.

Diet 
It feeds on a different foods which it can find in trees:
nectar and pollen from flowers
berries and nuts
insects - especially aphids and caterpillars
buds of young leaves
Hazel is the main food that dormice eat to fatten up before hibernation. The tree is also an important provider of insects.
Hornbeam and blackthorn fruit (if there are not many hazel trees)

The hazel dormouse needs different food sources at different times of year to survive.

Habitat 
Woodland
Hedgerows. These contain lots of different species and are connected to woodland.  The best ones are  high, and have not been cut for at least 7 years. This is because many shrubs do not begin to produce fruit for this long.
nestboxes
They usually only travel less than  from their nest.

Trees and shrubs which are important to dormice 
Hazel. This is the dormouse's main food source. It has a lot of branches, which makes it easier for the dormouse to move around. The hazel dormouse's Latin name avellanarius means hazel.
Oak. The dormouse eat the flowers of theoOak, as well as the insects that live on the tree. The acorns are not often eaten by dormice.
Honeysuckle. This tree's flowers and fruit are food. The dormouse uses the bark for nesting material.  
Bramble. The dormouse eats the flowers and fruits. The thorns give protection for the dormouse's nest.
Sycamore. The dormouse eats the pollen from this tree, as well as the insects that live on the tree.
Ash. Dormice eat the seed keys when they are still on the tree.
Viburnum lantana. The dormouse eats the fruits and flowers.
Yew. Dormice eat the fruits.
Hornbeam. Dormice eat the seeds.
Broom. Dormice eat the flowers in early Summer
Sallow. Dormice eat unripe seeds and the insects which live on this plant.
Birch. Dormice eat the seeds.
Sweet chestnut. Dormice eat the floers and the chestnuts.
Blackthorn. Dormice eat the fruit.
Hawthorn. Dormice eat the flowers in the spring. They sometimes eat the fruit

Predators 
 Badger, fox, stoat and weasel eat dormice. As nocturnal animals, they are also prey to owls.
 Lack of food - for example, if hedges are trimmed too often, or if other species (like squirrels) eat the food dormice feed on.
 Destruction of forest and hedgerow habitats.

References

Other websites 
Peoples Trust for Endangered Species  site describing the Hazel Dormouse and its conservation
Information and images  from the BBC
Extensive information and pictures
Pet care
A lot of facts, links and book reviews about the dormouse 
Dormouse nest-box construction 

Dormice
Mammals of Asia
Mammals of Europe
Mammals of Great Britain