Dormice are quite different from other mice. Part of the Gliridae family, within which are about 20 other species, mostly occurring in Africa. All have big black eyes, soft fur and fluffy tails.
Hazel (or Common) dormouse occurs throughout much of central Europe and as far north as Sweden. It is mainly found in southern England and Wales in the UK. They have been present in the UK since the last ice age. They are often found in woodlands with hazel, especially under coppicing regimes, as hazel is a favourite food. However, dormice have also been found in a range of different habitats including, scrub, hedgerows, culm grasslands, reedbeds, and gardens.
Hazel Dormice are protected under Schedule 5 of the Wildlife and Countryside Act (1981). This makes it illegal to:
- deliberately capture, injure or kill hazel dormice
- to possess, sell, control or transport live, dead or parts of hazel dormice
- to block access to, damage or destroy a resting place or breeding site
- to be deliberately or recklessly disturb dormice while in a structure of place of shelter or protection except with a special licence.
Dormice are listed in Appendix 3 of the Bern Convention which lists them as a protected faunal species under the Gliridae family. This requires involved parties to “take all appropriate measures to ensure the conservation of the habitats of the wild flora and faunal species.”
European Habitats Directive (92/43/EEC) is the means by which the European Union meets its obligations under the aforementioned Bern Convention, the aims of which are to maintain and/or restore natural habitats and wild species to a favourable status, and protection of habitats and species of importance. Hazel Dormice are listed under Annex 4 of animal and plant species of community interest in need of strict protection as part of the Gliridae family.
They are mentioned in the Conservation of Habitats and Species Regulations (2017) in relation to their designation as a European Protected Species under the Habitat Directive.
Hazel Dormice are a small rodent (7-9cm in size), similar in many ways to mice (Muridae family) in rough size and shape. Key characteristics of the dormouse are their golden yellow fur with a pale/white belly, long fluffy tail, and large dark eyes with dark rims. Overall they appear quite chubby, with a blunter muzzle supporting long dense whiskers and short hind feet. Generally, the tail is of similar length to the body (6-7cm), although they are quite fragile and easily damaged during fights or to predators, so may have shorter than expected tails
Hazel Dormice are predominantly arboreal and are highly agile, climbing and jumping at speed amongst trees in almost complete darkness. Dormice have prehensile feet and hind ankles that can rotate allowing them to hang upside down by their hind paws on tree trunks. They are generally reluctant to descend to the ground except during hibernation as they seem to be particularly vulnerable to predation by owls and foxes at this time. For this reason, they are mainly found in habitats with good connectivity to other suitable habitats. They have a strong association with ancient semi-natural woodland, particularly woodlands that have or have had a long rotation hazel coppicing regime. They prefer woodlands with a dense understory and open woodland glades (allowing light for flowering and fruiting plants).
Dormice spend a large portion of their life hibernating, in torpor or sleeping hidden away in nests which means that they are elusive creatures. Like bats, dormice undergo true hibernation, starting in October, or earlier depending on weather conditions. They weave small, apple-sized spherical winter nests from honeysuckle bark that can be found under leaf litter, tree roots or coppice stools where they can stay cool and humid while hibernating. They remain in their wintering nests until March, although they will wake periodically and may change the location to find better hibernating conditions. Even after this period, they can remain in the nest for a long time before emerging when conditions are favourable, but are likely to be active by April and actively visible in woodlands in May and June.
They then spend their time feeding as they can lose up to a third of their body weight over winter. In general, individuals that fail to reach a weight of 12-15 grams before hibernating are unlikely to survive the winter. If the weather becomes particularly poor, they can enter a state of torpor similar to hibernation but for shorter periods, to help preserve energy.
First broods are born in July (rarely in June) in maternity nests where they remain for six to eight weeks before being weaned and becoming independent. During this period, insects such as aphids and caterpillars are abundant and form a large part of the dormouse diet.
The remainder of the year is spent fattening up, ready for hibernation. This is when they gorge on fruits and nuts such as hazel, beech, blackberries, sloes and yew berries. Adults can reach weights of over 30g, doubling their weight in a month of good foraging. Hibernation behaviour seems to be triggered by the first frosts. It was initially thought that under piles of leaves amongst coppice stools were a favoured hibernation locations, but it may simply be that these were locations where they were most often encountered.
Hazel Dormice are not thought to be particularly territorial animals, although territorial behaviour has been observed, most often during the breeding season. For the most part, they are relatively sedentary species, rarely going much further than 70m from their nests. However, occasional dispersal has been recorded with individuals travelling 5km. Dormice occur in relatively low densities of 2-3 individuals per hectare, although this can increase to 5-10 per hectare in good quality habitats. It is thought that at least 20 hectares of suitable habitat is required to support a viable population.
Mating occurs in May and June, after which the females weaves several nests to raise her offspring. The alternative nests are available if she and her offspring are disturbed. Young are typically born in July or August with around four per litter, but occasionally two litters from two different females can be combined in one nest. After approximately 24 days the young look like adults, but smaller with greyer fur. They remain with their mother, joining her on foraging trips, for up to eight weeks until they are weaned. Initially, they don’t disperse far, building individual shelter nests nearby. Females rarely will have a second litter as they breed so late in the year anyway, but usually, any offspring from a second litter will not survive. It is unusual for more than two individuals from a first litter to survive through their first winter. However, individuals have been known to reach the age of five, which is old for such small mammals.
Dormice lack a caecum, a section of intestine which herbivores use to store the bacteria used to digest cellulose, so unlike many species, dormice are unable to digest grass and leaves for nutrients and so must utilise other resources.
Dormice are omnivorous, feeding on fruits, flowers, nuts, berries, but also insects.
Early on in the season, they spend the majority of their time up in the canopy feeding on the protein-rich pollen of early flowering species such as hawthorn, sycamore, wayfaring tree, elder and dogwood. In the early summer, the flowers of bramble and honeysuckle are important food sources, particularly the nectar-rich honeysuckle.
During the mid-summer periods, there is a period during which blossoms have faded, but fruits are not yet available. At this time insects such as aphids and caterpillars form a major part of their diet. Trees such as oak, hazel, and sycamore are known to support large numbers of insects on which to forage.
Once fruits and nuts become available, dormice spend more time in the shrub layer, fattening up on hazelnuts, blackberries, sloes, sweet chestnuts, beechnuts, elderberries, rose hips, willow seeds and yew berries.
As dormice do not venture far from their nests, they are mainly to restricted to habitats that are highly diverse and can provide enough seasonal food sources within a commutable area. This is why ancient semi-natural woodland with a long rotation coppice regime is often considered prime habitat for dormice as with the right management this will provide such conditions.
Due to the nocturnal and arboreal tendencies of dormice, along with the large portion of the year spent hibernating or sleeping, actually seeing dormice is a difficult task. Nut searches and tube or nest box checks are the most common method of identifying the presence of dormice.
While hazelnuts are a food source for a range of animals, including other rodents, birds and insects, the marks left by dormice when breaking through the hard shell to the edible flesh inside can be distinctive. They particularly like them when they are still green and the shells soft enough to gnaw through.
The key characteristics of a dormouse plundered hazelnut is a neat round hole which is smooth on the interior with teeth mark visible on the outer rim that occurs at a roughly 45° angle. This is caused as the dormouse enlarges the initially small hole by scraping around the edge with its teeth.
Natural nests may be encountered, these can be divided into several types including breeding or maternity nests, summer nests used by adult males or non-breeding females, shelter nests created by young close to their maternity nest, and winter nests. Summer nests are found off the ground in the shrub layer, in tree holes or amongst dense tangles of vegetation, with the maternity nests being bigger (grapefruit sized). Winter nests are smaller (apple sized) found on, under or close to the ground such as amongst leaf litter, under tree roosts or in coppiced stools.
In general, nests are made from honeysuckle bark, and grass with fresh leaves woven into the exterior (other materials used include hazel, oak, silver birch, bramble, ivy, beech, and hawthorn). Often they will have no visible entrance, unlike wren nests which can appear similar.
Being slow breeders, poor dispersers, and generally limited to species diverse habitats with a dense understory (which were historically maintained by practices which have now ceased), dormouse is vulnerable. Small populations are particularly vulnerable to chance events such as a season of poor food production, the low survival rate of a seasons offspring, or a skewed ratio of males to females, meaning there are reduced breeding numbers the following year, resulting in a spiralling decline.
Removal of hedgerows previously connecting habitat results in a barrier or causes them to be exposed to predation when traversing the gap.
Dormice have been known to be or are likely to be predated on occasion by a number of animals such as owls, foxes, stoats, ferrets and cats with the latter likely being the main cause of predation especially near to urban settlements. Other animals have been known to opportunistically predate them, particularly while hibernating, for example, badgers, wild boar, dogs, and even pheasant.
It is thought that previously the practice of letting pigs owned by commoners to range freely thought woodlands to feed on nuts and fruits during autumn (ancient rights of pannage) may have resulted in the reduction or even elimination of dormice from numerous areas, particularly small woodlands. Accidental tramping by humans, dogs, deer, wild boar or livestock may still be a potential threat.
As mentioned previously, species diversity is important for providing a range of food sources throughout the year for dormice, so the loss of diversity can have a significant negative impact on this species, along with habitat fragmentation by gappy hedgerows or complete loss.
Acer Ecology regularly carry out dormouse surveys. For more information about the Ecology Services we can offer, call us on 029 2065 0331, contact us on firstname.lastname@example.org or click here for examples of our work.