Hazel (or Common) dormouse
Native and localised. Rare and vulnerable to extinction
Declining in number and range
Hazel dormice have golden-brown fur and large black eyes and, distinctively, they are the only small British mammal with a furry tail. They are nocturnal and spend almost all of their time in the branches of trees during the summer, rarely coming down to the ground. They have sometimes been found asleep in old bird nests but they weave their own nests (often in brambles or other shrubs) from strips of honeysuckle bark or a similar plant, surrounded by a layer of green leaves. When conditions are cold or wet, or if food is scarce, dormice curl up into a ball and go into a state similar to hibernation for a short time (called torpor) in order to save energy. Between October and May dormice hibernate in nests beneath the leaf litter on the forest floor or in the base of hedgerows.
Head-body length: 6.5 – 8 cm
Tail length: 80% of body length
Weight: 20g (but can be 35g prior to hibernation)
Lifespan: Up to five years
The average litter size is four and these are typically born in July or August but litters may be born as early as late May or early June. Young dormice are weaned after about one month but may remain with the mother as juveniles before they become independent and disperse. They must reach a weight of between 15-18g to survive the winter hibernation. Dormice usually just have a single litter but those that breed early may be able to have a second.
Dormice are successional feeders and require a range of foods to allow them to feed while they are active. In spring they will feed on the flowers of oak, hawthorn, sycamore and willow and as the season progresses move onto later flowering shrubs such as honeysuckle and bramble. During the summer they take advantage of caterpillars, aphids and wasp galls and then they fatten up for hibernation on fruits and berries such as blackberries and hazelnuts.
Across its range dormice prefer the successional stage of woody vegetation; this is the new growth that arises after woodland management such as coppicing, ride widening, thinning or glade creation. In the UK the species tends to be more closely associated with old coppice woodland but they also occur in scrub habitat, old hedgerows and are sometimes found in conifer plantations.
Dormice live at low densities, even in ideal habitat and are not generally predated. They will however be predated by owls, weasels, grey squirrels and cats while they are active and they can be eaten by badgers and wild boar when they are hibernating at ground level. It is likely however that the greatest threat to an individual dormice is winter survival.
Dormice are slow breeders and poor dispersers and generally live in older woodlands with a well-developed understory often linked by old hedgerows. In the majority of woodlands in Britain the management required to maintain a well-developed understory has ceased, making them less suitable for dormice. Inappropriate management of hedgerows, or their removal, has meant that woods that have lost their dormice will not be repopulated. The future effect of climate change on dormice is unknown.
Status & conservation
Native and localised. Hazel dormice are rare and vulnerable to extinction in the UK. They are a priority species in the UK Biodiversity Action Plan. They are protected under the Wildlife and Countryside Act 1981.
Population size & distribution
The UK population is unknown but there has been a long term decline in both number and range; recently there is an indication that the decline is slowing and as part of an ongoing dormouse reintroduction programme the current range is slowly being extended. The current dormouse range is Southern England and South Wales and along the English/Welsh border. Even where dormice are considered present their distribution is patchy.
Did you know?
Wood mice, bank voles and hazel dormice feed on hazelnuts by gnawing a round hole in the shell and each leaves distinctive marks. The tooth-marks of dormice run parallel to the edge of the hole, rather than outwards from its centre, so that the rim looks smooth, and there are few tooth-marks elsewhere on the nut. In contrast, the tooth-marks of mice and voles run outwards, so that the rim of the hole looks like the milled edge of a coin.