Devon Mammal Group

Hazel Dormouse

Hazel Dormouse

Photo: Richard Knott

Common names

Hazel Dormouse, Common Dormouse (although neither common nor restricted to Hazel)

Scientific name and classification

Mammalia - mammals
Order Rodentia – squirrels, beavers, mice and voles, dormice, birch mice, porcupines, coypu
Family Gliridae – dormice
Genus and species Muscardinus avellanarius

‘Musca’ means ‘mouse’; ‘dinus’ denotes ‘little’; ‘Muscardinus’ may also refer to a resemblance to one of the life stages of Glis glis, the related Edible or Fat Dormouse. ‘avellanarius’ derives from the scientific name for Hazel Corylus avellana.

‘Dorm’ probably derives from French ‘dormir’ to sleep, alluding to hibernation and torpor. Another suggestion is that ‘dor’ means ‘round’ like a clock face, referring to the habit of rolling into a ball.

Conservation/protected status

  • International: IUCN status: 2009 classification as Least concern; was formerly Low risk/near threatened [1]
  • European: All dormice in Europe (5 species) are European Protected Species under Appendix III of the Bern Convention, incorporated into UK national legislation as ‘the Habitat Regulations’ 1994 and 2010
  • National:
    • Schedule 5 species listed under the Wildlife Countryside Act 1981 (as amended)
    • A Species of Principal Importance under the NERC Act 2006
    • Biodiversity Action Plan priority species: in the national, regional, Devon BAP, and also in Local BAPs in Dartmoor, Exeter, Teignbridge and others

This means that it is illegal to disturb or handle a dormouse without a special licence. Species of Principal Importance and Biodiversity Action Plan listing mean that impacts on dormice must be taken into account for any development works affecting dormouse habitat, and that projects will be carried out for the active conservation and restoration of dormice within their known and former range.

Current and local status

Across Europe and nationally all dormouse species are thought to have declined seriously over the last 100 years. The Hazel dormouse, which is the only native dormouse species in the UK, has apparently disappeared from half of the UK counties in which it used to be found. National range is now concentrated in the southern counties, particularly Kent, west Dorset, Somerset, Devon and also Hampshire, Surrey, Sussex and the home counties. Dormice are present in south and mid Wales, and counties along the Welsh border. There are some known sites in East Anglia and Cumbria. Otherwise dormice seem to be rare in the north and midlands, regions which have suffered the major decline, and has never, or rarely, been recorded in Scotland [2, 3].

National survey results suggest that dormice have continued to decline, particularly in the northerly part of their range, with further declines within northerly areas of 50% (giving an overall national decline of 10%) between 1988-2008. In the south and south west populations remained relatively stable through this time. Analysis in 2009 suggested the national decline had slowed for recent years leading up to 2008 [2, 4 ].

Dormouse records in Devon

Dormouse records in Devon

Devon’s woods and hedgerows are a UK stronghold for the dormouse. There are well over a hundred recorded sites in the county. Core areas are east Devon and along the west Dorset and west Somerset border, which in particular has high concentrations of dormouse records. Records seem more scattered but are still numerous across mid and north Devon. Other areas with frequent records include the South Hams, Teignbridge and most of Dartmoor. Curiously south west Devon, areas around Plymouth, and north west Dartmoor have comparatively fewer dormouse records [5], despite apparently suitable habitat and repeated surveys.

General description

Relatively bulky body and short muzzle compared to other mice; head and body length 60-90mm with 55-80mm tail. Long whiskers (~30mm) and large black eyes (probably both adaptations to nocturnal habits). Weight 15-30g though fluctuates through season and increases towards hibernation to 30-40g or more [6]

The most obvious distinctive feature is the furry tail (though some have fore-shortened tails where tail ends have been damaged and shed, through fights or predators). Tails occasionally have white fur tips. Damaged tail stumps often produce long discoloured hairs [6, 7]. Fur coloration is characteristic, with dorsal fur yellowy, varying from brown to orange, and a white underbelly. Juveniles have grey fur.

Wood mice are often confused with dormice. The dormouse has a blunter face and the build is more stocky; wood mice are sleeker, more rangy, with brown dorsal fur, while the tail is barely furry at all. Wood mice are very common and will visit garden bird feeders and houses.

Verification of records

Records can be validated by DBRC through

  • Photograph
  • Nibbled nut
  • Dormouse nesting evidence
  • Description from a reliable recorder.

Habitat

Associated with woodlands, hedges and scrub. In Devon, any woodland, species-rich hedge or area of woody scrub should be considered as possible dormouse habitat. Dormice are also to be found in other, non-deciduous woody habitats. This includes conifer plantations, both where plantations have been cultivated on former ancient woodlands sites, and among pure conifer forestry stands (Douglas Fir and Spruce seem favoured), coastal scrub, intensively managed hedges, stands of pure Birch and gorse, dense Rhododendron, mixed conifer – Laurel scrub, road verges and wet woodland. They have also been recorded on relatively open, tree-less habitats such as heathland and culm grassland, nesting among gorse and low down in grass tussocks, and in reedbed [3, 8]. Considering feeding requirements have a strong link with woodland habitats in studies, it is not well understood how populations are able to persist in other sorts of habitats. Dormice have also been recorded visiting garden bird feeders and bird boxes.

Behaviour and life history traits

Mainly nocturnal and arboreal, moving swiftly through canopy, understorey and scrub cover. Feeds on nuts, soft fruits, flowers (hazel, bramble, blackthorn, elder, ash and maple keys), insects, may take sap and eggs. Insects may be important in diet when flowers and fruit are unavailable. Dormice have no caecum, so do not have the means to digest quantities of green plant matter. Recorded distances travelled in one night are 70-90m within a home range.

Nesting takes place in tree holes and behind bark, also among dense thorny scrub and in hedges, sometimes quite low down (see below for a description of a nest). Bird nests and squirrel dreys may be adopted as nest sites.

Dormice can enter torpor, most frequently early in the season. This has been linked to conserving energy during temporary adverse climatic conditions and shortages of food.

Territorial behaviour is shown up to and during breeding, but may diminish later in the season. The breeding season lasts May-September, usually with one litter per year (June-August), sometimes two, with late litter and breeding by young-of-the-year, possibly according to weather conditions and amount of food available.

Breeding in relation to sex ratios is not well understood. Early results of DNA studies suggest polygamous breeding. Gestation lasts 22-24 days. Litter size can vary between 2-7. Weaning takes 6-8 weeks. There is some suggestion that communal crèche nesting, perhaps among related females, may take place. On independence juveniles disperse from the natal nest.

Dormice have been recorded to be relatively sedentary, staying within an area throughout their life, once having established a home range. However occasional adult dispersal movements are known, travelling directionally and far from the home range. The furthest recorded dispersal has been 5km [7].

In autumn dormice put on weight quickly to build up fat resources for hibernation. Many aspects of hibernation are not well understood. Hibernation often takes place at or just below ground level, under leaf litter or among tree roots, in a tightly enclosed nest. Hibernation lasts from November-April though there may be brief periods of arousal and activity during this time. Timing of hibernation can be affected by time of breeding and food availability.

Dormice in Mediterranean areas do not hibernate, nor show a seasonal breeding pattern, which may be due to warmer, more stable, and drier climatic conditions.

Dormice have few predators. Woodmice, foxes and, on the continent, wild boar may take dormice when they are vulnerable during hibernation. Tawny owls rarely catch dormice but have been found to be the main predator in some studies of European populations. Woodmice apparently compete with dormice for food and nest sites, and might predate them while they are in torpor.

Lifespan is 1-2 years in the wild, sometimes to 4 years or longer. Highest mortality is in the first winter due to starvation during hibernation [2,3,6,7].

Where to see dormice in Devon

Dormouse map

Map of Dormouse distribution in Devon (click to view full size). This map represents the current records held by the Devon Biodiversity Records Centre (DBRC) - if you have your own sightings to contribute please report them via our records page.

Not commonly seen unless taking part in an organised nest box check at a known site. In some parts of Devon, dormice have been observed visiting garden bird feeders and found in garden bird boxes. During natal dispersal there may be a higher chance of finding dormice in new areas and novel habitats as numbers are at a seasonal peak, and juveniles are attempting to find new territories.

Dormice are strictly protected. It is illegal to touch, handle, or otherwise disturb dormice without a Schedule 5 licence. Some owners of nature reserves might organise events for interested parties, or individual licensed handlers may be willing to allow individuals to accompany them on a nest box check. However please note that it is illegal to check boxes without an appropriate licence, and it would not be permitted to look for dormice outside of a pre-arranged event supervised by a licensed handler.

Common survey techniques

Feeding signs.

Nibbled hazel nuts and blackthorn stones are opened in a distinctive way, which can be used to determine presence. Many animals eat nuts, and feeding signs need to be distinguished.

  • Bank Voles leave a round hole without tooth marks on the outside of the nut.
  • Woodmice leave a more irregular hole with tooth marks on the outside of nut while gnaw marks cut across perpendicularly, pointing towards the middle of the hole, uneven and rough to the touch.
  • Dormice leave tooth marks on the outside of the hole while gnaw marks follow the circumference of the hole, very neat and smooth to the touch.

One way to visualise the difference is to imagine woodmice use a chisel, and dormice a screw-top lid.

Nests, nestboxes and nest tubes.

Nestboxes are used as part of the national monitoring programme. Boxes are used by other species such as birds, hornets, pygmy shrews, wood mice, and slugs; dormice will use birdboxes and bat boxes. Nest tubes are often used for shorter term studies. Dormice may be present at a site but not use boxes or tubes provided.

Nests.

Direct searching for nests can be attempted among bramble and hedge habitats, though nests are not likely to be revealed until the end of the season when vegetation dies back. Crouching down to look upwards through vegetation, to see nests against the light, is the best method.

Nests are quite distinctive: green leaves or other green vegetation is often laid on top of the nest. Nest material is characteristically woven together. Commonly used materials are stripped honeysuckle bark, grass, and leaves; depending on what is available, nests may include moss, pine needles, gorse, bluebell stems, or lichens. Any nest containing stripped honeysuckle bark, and showing material with definite evidence of weaving into shape, is probably a dormouse nest.

In some habitats, where grass is the only nesting material available, dormouse nests may be confused with harvest mouse nests and, on the ground, possibly vole nests. Harvest mouse nests are very small and attached to a grass stem (but often fall to the ground); it may be possible to tell the difference between them from the way grass leaves are cleaved in two [3].

A woodmouse nest is a loose jumble of brown leaves. Bank vole nests can also comprise leaves, partly moulded into shape. Bird nests are mossy, usually mud-lined, and, apart from enclosed nests like a wren’s nests, can be seen to have an open central saucer depression in the top. Nests can have successive tenants, with modifications to dormouse, wood mouse or bird nests showing characteristics of each tenant, making the most recent occupant more difficult to determine.

Other field signs

Honeysuckle with stripped bark, and droppings, can be looked for, but it would take some practice to identify these as dormouse signs.

Current studies locally

Nestbox monitoring

Dormouse populations have been monitored since 1988 by the Dormouse National Monitoring Programme, administered by the People’s Trust for Endangered Species (PTES). Sites participate in the scheme voluntarily and checks are carried out usually monthly between April – November, by local site managers and volunteers. There are approximately 20 nest box schemes in Devon that take part in the national programme. Sites are owned or managed, for example, by National Parks, Local Authorities, AONBs, Devon Wildlife Trust, South West Water, and privately.

Devon records are kept by Devon Biodiversity Records Centre. A National Inventory of dormouse sites, collated from the national nestbox programme and nut hunts, is kept by PTES. Further nestbox monitoring sites for the national programme are needed in Devon, especially in East Devon area and west Devon, Tamar and Tavy valleys. Many Devon sites took part in the pilot study of nest tubes, Chanin P and Woods M (2003) Surveying dormice using nest tubes results and experiences from the South West Dormouse Project English Nature Research Reports no 524, in the course of which dormice were recorded on Devon culm grassland and heathland sites [8]

Hedges

Devon Hedge Group organises Hedge Week each year, which often includes dormouse-themed events and activities.

PTES organises a Hedges for Dormice project nationally which involves studies of hedges in identified dormouse ‘hotspots’, across the country in key areas. There are 5 such PTES hotspots in Devon (North Devon, East Devon, Teignbridge/east Dartmoor, South Dartmoor and South Hams). Help surveying Devon hedges as part of this project is needed.

Rob Wolton has studied dormouse nests found on his Devon farm.

R Wolton (2009) Hazel dormouse Muscardinus avellanarius (L.) nest site selection in hedgerows
Mammalia vol 73 (issue 1): 7-12

Nut hunts

National ‘nut hunt’ surveys took place in 1993 and 2001, administered by PTES. A further national survey is taking place 2009-2010. See above for description of nuts. The aim is to visit previous sites, and find new sites. There are approximately 120 nut hunt sites across Devon. Help surveying sites is welcomed.

The discovery that hazel nuts are nibbled in a characteristic way, so can be used to determine dormouse presence, was made by HG Hurrell in Devon. Elaine Hurrell carried out the first modern dormouse survey.

Elaine Hurrell and Gillian McIntosh Mammal Society dormouse survey, January 1975 - April 1979 (1984) Mammal Review 14 (1): 1-18

Development control surveys

Dormice are a European Protected Species, which means developments affecting any potential dormouse habitats require surveys to be carried out as part of planning applications. Because dormice are widespread in Devon, numerous surveys are carried out through this means.

Diet, tracking, hibernation and DNA

Exeter University is hosting a PhD project studying feeding by analysis of droppings, hibernation behaviour relating to diet, use of tracking tubes as a monitoring technique, and dormouse DNA in the south west. If you can collect dormouse droppings or participate in a box scheme and would be able to help please contact
Cheryl Mills e-mail cm271@exeter.ac.uk
School of Biosciences, University of Exeter, Cornwall campus, Penryn, Cornwall TR10 9EZ

Captive breeding, post mortem, nest composition, hibernation and habitat studies

Whitley Wildlife Trust (Paignton Zoo) is involved with two national projects: captive breeding for reintroduction schemes, and dormouse post mortem studies.

Each year Paignton Zoo hosts student studies, which have looked at nest material, feeding behaviour before hibernation, and habitat use by dormice at Slapton Ley. Slapton Ley also takes part in the national nestbox monitoring programme.

Biodiversity Action Plan for dormouse in Devon, county records, occasional student projects

Devon Wildlife Trust is the county ‘champion’ agency for the dormouse Biodiversity Action Plan in Devon, with responsibility for reporting on progress on local conservation targets. As part of this there is a ‘Devon dormousers’ contact group, which is an informal network of dormouse workers. The group holds an annual meeting and hosts a web forum page.

DWT and DBRC have supported student projects on habitat modelling using DWT reserves, and on dormouse use of domestic gardens.

Devon Dormousers web forum http://pets.groups.yahoo.com/group/devondormousers

Devon Mammal Group small grants scheme

DMG’s small grants scheme has supported the North Devon Dormouse project and the DBRC garden study, and the 2009 Great Nut Hunt in Devon.

Help needed

  • All records appreciated by DBRC – nuts, sightings, results of consultants’ surveys
  • Setting up of new nestbox schemes that can contribute to the national scheme
  • DMG receives a number of requests from people trying to gain practical experience towards a dormouse licence. If you are a licensed handler, participate in a box scheme and would be willing to take on trainees, please get in contact with DMG or the Devon Dormouse BAP group.

References

[1] IUCN website http://www.iucnredlist.org/details/13992/0
[2] Bright P, Morris P and Mitchell-Jones T (2006) The Dormouse conservation handbook second edition English Nature, Peterborough, Cambs., UK
[3] Eden S (2009) Living with Dormice - The Common Dormouse: real rodent or phantom of the ancient wood? Papadakis Publisher, Winterbourne, Berks., UK
[4] PTES The Dormouse Monitor various issues
[5] DBRC records
[6] Macdonald D and Barrett P (1993) Collins field guide Mammals of Britain and Europe Harper Collins, London, UK
[7] Juškaitis R (2008) The Common Dormouse Muscardinus avellanarius: ecology, population structure and dynamics Institute of Ecology of Vilnius University Publishers, Vilnius, Lithuania
[8] Chanin P and Woods M (2003) Surveying dormice using nest tubes results and experiences from the South West Dormouse Project English Nature Research Reports no 524, English Nature, Peterborough, Cambs., UK