Dormouse surveys

The hazel, or common, dormouse is a small member of the dormouse family, with adults reaching a body length of six to nine centimetres and a tail that is usually around six centimetres long. They have bright golden fur with a pale underside and are most easily distinguishable from other small British mammals by their long fluffy tails.

Adult dormouse waking from torpor

Adult dormouse waking from torpor. Photo by Courtenay Holden.

The UK population of hazel dormice has declined significantly over the last fifty years or so, mainly due to accelerating habitat loss, a decline in quality of the habitats that remain, inappropriate habitat management and habitat fragmentation. Hedgerow removal has resulted in the reduction of wildlife corridors between woodland areas and dormice are generally reluctant to cross open ground to colonise other areas, thus are vulnerable to local extinctions when suitable habitat disappears. Dormice also have a specialised diet not usually found in young, isolated or small areas of woodland.

The hazel dormouse spends up to three-quarters of its life asleep, either in hibernation (between October and April) or, if spring or summer weather is poor, in torpor (a sleep like state used by animals to survive colder temperatures by saving energy). In the spring and summer, dormice build nests in trees, shrubs and other habitats, whilst in the winter they hibernate in leaf litter and root systems below the woodland or hedgerow floor.

Dormice breed between May and September and usually produce one litter (sometimes two) with an average of four young.

Where are dormice found?

Hazel dormice can be found in long-rotation hazel coppice, deciduous woodland, species-rich hedgerows and dense scrub. In recent years, they have also been found in habitat previously not thought suitable, such as plantation woodland and dense areas of Phragmites australis. In the spring and summer, they typically build nests using honeysuckle bark and grass a metre or so above the ground and they may also use nest boxes and tubes deployed for the purposes of surveying. Dormice emerge and forage in the canopy after dark.

Dormouse nest in a nest box

Dormouse nest in a nest box

Legislation

Dormice are legally protected under the Conservation of Habitats and Species Regulations 2010 (the Habitats Regulations), UK legislation that has its roots in European law, as well as the Natural Environment and Rural Communities Act 2006 (Section 41) and the Wildlife and Countryside Act 1981. Where an extended Phase 1 habitat survey of a development site identifies the presence of habitat potentially suitable for dormice, or where desk study records of dormice are found within the vicinity of the site, dormouse surveys may be recommended.

Surveying dormice

Survey methodology for dormice reflects the life-cycle of this species and usually requires the installation of artificial nest boxes or tubes in woodland or hedgerows, which are checked on a monthly basis by an appropriately licenced ecologist. Standard guidance for dormice surveys usually recommends this as the most robust and reliable survey method, although other methods may also be used to compliment this.

Ecologist Steve Docker checking dormouse tubes

Ecologist Steve Docker checking dormouse tubes. Photo by Diana Clark.

Survey methods:

  • Searching for gnawed hazel nuts is the most efficient method, but only where hazel is present. This is generally not recommended to demonstrate likely absence in relation to any development site.
  • Nest tubes are used particularly where hazel is absent. They are inexpensive and made from a plywood tray housed in black plastic. Dormice use the tubes for shelter and sometimes breeding, and the tubes can be easily checked for occupants by sliding the plywood tray out to reveal any nests present. Deploying a minimum of fifty tubes per site is considered an adequate sample size to robustly determine if dormice are present or likely absent.
  • Nest boxes are best suited to long-term monitoring, particularly within woodland sites. They are more robust than nest tubes and generally last a number of years before replacement is required.
  • Other methods include nest searches, hair tubes (which can only be used in the summer) and trapping, although the latter is labour intensive and needs a licence. These methods have a low ‘hit rate’ and are not generally recommended.
Gnawed hazel nuts. From Dormouse Conservation Handbook page 23

Gnawed hazel nuts. From Dormouse Conservation Handbook page 23

Different methods must be carried out at specific times: nest tubes and nest boxes can be used between March and November, whilst nut searches can be carried out all year to confirm presence only.

At Baker Consultants, Senior Ecologist Diana Clark is our dormouse expert and has held a dormouse licence for a number of years. All of our dormice surveys follow guidance within The Dormouse Conservation Handbook 2nd edition.