Dormouse Surveys

The common or hazel dormouse is a small nocturnal mammal which can be found in deciduous woodland, species-rich hedgerows and scrub, but will also use a number of habitats that, until relatively recently, were considered atypical such as gardens and conifer plantations. Dormice are arboreal creatures and will utilise networks of hedgerows and tree canopies in woodlands in order to move around. Dormice require habitats which will provide them with a range of food, such as flowers, fruits, insects, pollen and nuts, throughout most of the year and suitable ground cover for them to hibernate in. Dormice are active between late April and late October, spending the remaining months in hibernation.

Survey Types & Timing

If a development is likely to affect areas which are likely to be used by dormice, such as woodland or linked hedgerows, then a dormouse survey will often be required to establish the presence or likely absence. Survey methods involve;

Dormouse nest tube survey – Typically a minimum of 50 nest tubes should be installed on site amongst suitable vegetation and checked for dormice and/or nests. These surveys can be undertaken at any time during the dormouse active season (April-October). Each month is assigned an ‘index of probability’ value of finding dormice. The overall thoroughness of a survey calculated using the index of probability values for the months surveyed and the number of nest tubes used. The Dormouse Conservation Handbook, published by English Nature (2006), recommends that dormouse absence should be considered likely from a site if a search effort score of 20 or more has been achieved without finding evidence of dormouse in nest tubes.
Dormouse hazelnut survey – This can be an effective method of establishing dormouse presence on sites which contain hazel trees and entails a methodical search for gnawed hazel nut shells. The optimal period for finding fresh hazel nuts with visible gnaw marks is generally between mid-August and December.

A survey licence, issued by the relevant statutory body, is required for potentially disturbing activities such as checking nest tubes and dormouse boxes and for searching for dormouse nests (if they are likely to be present).

Legislation & Planning

The dormouse has become an increasingly rare species due to factors such as habitat loss and fragmentation. The dormouse is fully protected under the Wildlife & Countryside Act (1981) and the Habitats Regulations (2010), which makes it an offence to:

Intentionally or deliberately capture, kill, or injure dormice;
Intentionally or recklessly damage, destroy, and disturb dormice in a place used for shelter or protection, or obstruct access to such areas;
Damage or destroy a dormouse place of shelter or protection;
Possess a dormouse, or any part of it, unless acquired lawfully; and
Sell, barter, exchange, transport, or offer for dormice or parts of them.

Local Planning Authorities are obliged to request dormouse surveys to accompany planning applications where they believe there is a reasonable likelihood that dormice are present.

The Next Step

If it is possible to retain and protect areas of hedgerow or woodland, used by dormice, during development then this should be the first option. If this is not possible a European Protected Species Licence will be required and a detailed strategy of mitigation and compensation implemented.