Dormouse Surveys

Background

The hazel dormouse (Muscardinus avellanarius) was once a common sight across much of the UK; however, loss and fragmentation of suitable habitat have contributed to a significant decline in populations. As such the hazel dormouse is afforded both UK and European protection which makes it an offence to: deliberately disturb, capture, injure or kill them; damage or destroy their breeding or resting places; disturb or obstruct access to any place used by them for shelter; possess, or sell a wild dormouse.

The hazel dormouse has a restricted UK population. They occur mainly in the southern counties especially: Devon, Somerset, Sussex and Kent, but are also patchily distributed across much of Wales, Cheshire, the Midlands and Yorkshire. Although hazel dormice are usually associated with broadleaved woodlands they occur in a wide variety of habitats including rural gardens, dense rhododendron, and reed beds. Therefore, surveys should not be restricted to optimal habitat and instead should be undertaken in any woody habitat within their known range, which is likely to be affected by works.

Hazel dormice can be affected by various activities including: woodland and hedgerow management, the removal of hedgerows, woodland clearance, noise and lighting. In the majority of cases sensitive management can help prevent harm to dormice or their habitats, however, if this cannot be avoided a mitigation licence from Natural England will be required. EMEC Ecology can carry out hazel dormouse surveys, mitigation and licensing.

Timing

Hazel dormouse surveys should be carried out during the active season, usually April to November, dependent on the area of the UK. After this period the dormice enter hibernation. Nut searches can be carried out at any time of the year however they are best undertaken between September and December as the distinctive gnaw-marks can deteriorate over time. This method is restricted to habitats which support stands of fruiting hazel. Preliminary habitat assessments can be undertaken throughout the year, but are more beneficial if undertaken in conjunction with nut searches between September and December.

Methodology

Prior to undertaking a hazel dormouse survey a preliminary habitat assessment will be undertaken and historical records consulted to determine the potential for dormice to be present.

A combination of the following methods may then be utilised in order to survey for the presence of hazel dormice:

• Nut searches
• Searching for wild nests
• Nest-tube and nest-box surveys
• Footprint tunnels

Nut Search

A search for wild nests and gnawed nuts (if hazel is present) is conducted to search for evidence of hazel dormouse activity in suitable habitats on Site. The survey will be carried out by an appropriately experienced ecologist within the active season (April to November, inclusive). This survey is only appropriate where a minimum of 100 hazel nuts (excluding nut caches) can be collected across the Site.

Nest Tube Survey

A hazel dormouse (Muscardinus avellanarius) survey will be undertaken on-site in line with the guidance provided within the Dormouse Conservation Handbook (Bullion et al., 2025[1]). Nest tubes will be placed across the site (minimum of 50 tubes required by guidance) in suitable habitat, to be deployed at 20 m intervals if possible. The tubes will be checked for signs of nest-building activity or other use by dormice each month throughout the deployment period. During each visit a search for wild nests and nut search (if hazel is present) will also be undertaken to search for evidence of dormouse activity. Nest boxes can also be installed as a supplementary measure; however, this is not essential to establish likely absence.

The surveys will be carried out by an appropriately licensed ecologist within the active season (April to November, inclusive), accompanied by an assistant for tube deployment and collection. The nest tubes must be deployed by September at the latest in good quality habitat or by April in poor quality habitat to have sufficient confidence in the results. Surveys are concluded once dormouse presence has been confirmed, or once the required survey effort has been reached to conclude that there is a high probability of dormouse absence. As such, it is usually beneficial to deploy nest tubes at the start of the survey season, increasing the likelihood of early detection and reduce the potential for delay.

Footprint Tunnel Survey

The third recognised survey method, which can be utilised alongside or instead of Nest Tube Survey, is the use of footprint tunnels. Dormice footprints are sufficiently distinguishable from those of other small mammals and as such can be used to confirm presence or likely absence given sufficient survey effort.

Footprint tunnels should be deployed between May and October by a suitably experienced ecologist. A minimum of 50 tunnels should be deployed, at intervals of 15-20 m, except where the habitat extent is limited, in which case a minimum of 30 can be deployed. Tunnels should be visited at least twice per month to replace ink and tracking media. The tracking media will be analysed after each visit to establish if dormice footprints have been recorded. To have sufficient confidence that dormice are absent, 50 tunnels should be checked for three months. If less tunnels are deployed due to limited habitat extent, then the survey effort is increased to four months for 40 tunnels or five months for 30 tunnels. As with the other survey methods, once dormouse presence is confirmed, the survey is concluded.

Following the Survey

Report

We will provide a report detailing the survey methodology and results as well as providing an evaluation of the species recorded and recommendations for general mitigation measures, further surveys and / or consultation, as appropriate. The report will be provided as soon as possible following the survey, however; should you have a specific date for submission of a planning application we will do our utmost to accommodate this.

Dormouse Mitigation

Dependent upon the development proposals and the survey results, a variety of mitigation solutions may be proposed by EMEC Ecology. Some mitigation strategies must be undertaken under a European Protected Species (EPS) licence, which EMEC Ecology can arrange on behalf of the client.

[1] Bullion, S., Wolton, R. & White, I. (2025). Hazel Dormouse Conservation Handbook, Third Edition. Mammal Society.