About Dormice

The hazel dormouse Muscardinus avellanarius is extremely elusive and increasingly rare. It is unlike other rodents, being long-lived and highly specialised in its ability to hibernate.

Description

The hazel dormouse is a rare native small arboreal (tree-living) rodent, with a body approximately 75 mm long and a tail of a similar length. Hazel dormice have a furry tail, golden brown fur, large black eyes and long whiskers.

Life Cycle

Dormice hibernate at ground level over winter in closed woven nests just under the ground surface, often at bases of trees or piles of leaves or logs. They then spend the spring, summer and autumn months active in the tree and shrub canopy.  On waking from hibernation around April, dormice take advantage of early buds, flowers and small insects to feed and regain weight lost during hibernation, in preparation for breeding.  Summer breeding nests often have an inner woven nest with layers of green leaves on the outside. Mating can take place as early as May and after a gestation period of about three weeks, the first litters can be born in late May or early June.

Life Stages

In Britain, early litters are relatively unusual and mating usually occurs in either June or July, with the majority of litters born in either August or September. Litter size is approximately four and they are born blind, pink and naked. Young dormice remain in the nest where they are cared for by their mother for approximately four weeks after which they become independent. The young animals can be separated into distinct stages of development which are pinks, grey eyes closed and grey eyes open (these are the unweaned young stages) after which they are recorded as juvenile (post-weaned young of year) and adult (an animal that has survived its first hibernation).

Range

Dormice are considered to be relatively sedentary animals with males occupying an area of approximately 0.5 hectares and females less. They have been radio-tracked to travel up to 80-100m from their nests to access food. Juveniles have been shown to disperse up to 500 m from their place of birth, but they are likely to be able to move up to 1km in suitable habitat.

Diet

The diet of the hazel dormouse varies throughout the year and demonstrates the importance of a variety of shrubs and trees in the habitat they live in.  Early in the year, dormice will feed on the pollen and nectar of flowers of species including hawthorn, honeysuckle and sycamore, moving to other species as the flowers become available, such as bramble. Over summer, insects form an important part of the diet, as there are fewer flowers available on woodland or hedgerow shrubs and trees, and in late summer and autumn, beech nuts, hazelnuts, seeds and berries are a key food, allowing dormice to fatten up ready for hibernation over winter. Nuts that have been nibbled by dormice are easy to identify, as they carve out a circle with an almost smooth inner rim. Looking for nibbled nuts is a good survey technique.

Habitat

Hazel dormice typically inhabit broadleaved woodland, scrub, and hedgerows composed of native shrub species.  As their name suggests, hazel dormice are closely associated with hazel Corylus avellena and they utilise hazelnuts as an important food source in the autumn. Dormice are not found exclusively in woods with hazel however and can live in habitats where hazel is absent. The most important factors required for dormouse habitat are: a tree or shrub structure that allows dormice to move around freely and safely off the ground; a good supply of natural food throughout their active year; dense foliage or nest holes in which to build nests to breed and raise young during the summer; and suitable, undisturbed places to hibernate at ground level.  Hazel dormice can also be found in some conifer woodland and they are occasionally recorded in gardens and other less predictable habitats.

Hazel dormice live mostly in deciduous woods with a well-developed understory and in most parts of their range they prefer the early successional stages of woody vegetation over the high canopy, unmanaged woodland that is so common in our current landscape.  This is reasonable, as a woodland in active, sympathetic management, such as coppice or coppice with standards, results in a varied age structure, allowing a variety of plants to flourish in different areas of the wood in any one year, thus providing consistent sources of food and nesting habitat for dormice in the wood.  Well-managed, ancient woodland would be an ideal habitat for dormice, as the longstanding nature of the wood (‘ancient’ in this case means a continuous woodland on the site since at least 1600) would provide a wide range of species and the existing management should give a good structure.

It is most likely that the name ‘hazel’ dormouse came about because hazel coppice was where dormice were most often found, by coppice workers coming across hibernating dormice during winter. This would simply be because hazel coppice was the most common form of worked coppice in the hazel dormouse range, so where most coppice-workers were working!

Threats

The main existing threat to the hazel dormouse is human activity.  Since humans started clearing the land thousands of years ago, large tracts of woodland have become smaller and fragmented – a process exacerbated in recent centuries through relatively rapid development and urban expansion.  In order to recreate the natural processes that would once have taken place in large woodlands, resulting in the types of woodland habitat that we think dormice would have historically inhabited, active management by people is needed.  Up until the middle of last century this happened through coppice and coppice with standards, but since our reliance on woodland products reduced, unfortunately many woodlands have fallen out of management and are left to ‘go wild’.  This is a process that results in a high canopy woodland, with little or no understorey, little or no regrowth and little variety in plant species – all factors that have contributed to the demise of the hazel dormouse in woodlands.

Natural predators include owls, wild boar, badgers and domestic dogs and cats, however dormice are not easy to come by and live in low densities, so no one of these species includes the hazel dormouse as a major component of the diet. Dormice are more likely to be a welcome supplement to an animal’s diet, caught by an owl through luck, or dug up by chance during hibernation, by a foraging animal. Domestic cats living near dormouse habitat are perhaps the biggest animal-based threat to dormice, especially as our dwellings (and therefore cats) encroach more and more into the countryside and dormouse-inhabited woodlands. Species that may have a greater negative impact on dormice are deer (that eat the developing habitat that dormice occupy) and grey squirrels which can eat a huge quantity of hazelnuts often before they mature.

They are vulnerable to extinction and are a conservation priority species in the UK and a European Protected Species.

For more information, visit our Protection and Guidance page.

Distribution

Hazel dormice are widespread in Europe from the Mediterranean to southern Sweden, East to Russia and west to southern France. Island populations occur in Great Britain, Corfu and Sicily.

In Britain the native range of the dormouse extends throughout England and Wales. The species is generally more common in the south than in the north but even where the population is greater the distribution can be patchy. In the 21st century the dormouse has become extinct from many of the northern and midland counties over the past one hundred years and the species is now mainly confined to the southern counties of Britain, the English/Welsh borders and east and south Wales. There has been an ongoing effort to reintroduce dormice to those areas where the species has become extinct.

Current Distribution of Dormice in Hampshire

Hazel dormice have been recorded across much of Hampshire, but with particular concentrations of records to the east of Andover including along the A303 corridor, to the east and west of Basingstoke, along the M3 corridor north of Winchester, across parts of the South Downs National Park and near Park Gate, Fareham.  These records consist of dormouse sightings and other evidence of their presence within habitat, including nests and characteristically chewed hazel nuts.  Of course, an absence of dormouse records does not mean that dormice are not present, merely that they haven’t been spotted yet!  The Hampshire and Isle of Wight Dormouse Group is therefore working with other nature conservation groups within Hampshire to increase our knowledge about dormouse presence and distribution across the county, through numerous projects including the National Dormouse Monitoring Programme.

We are currently undertaking a county wide project to survey for dormice using footprint tunnels – to find out more about this and to get involved please visit our County Survey page.