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Dormouse

Background

DormouseThe common, or hazel, dormouse Muscardinus avellanarius is a nocturnal and highly arboreal rodent that feeds on a variety of food sources including  flowers, fruits, insects, pollen and nuts.  It is 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 active between late April and late October, spending the remaining months in hibernation.  Distributed primarily in southern England and Wales, the dormouse is absent from Scotland, Northern Ireland and the Republic of Ireland.

Conservation status

Common dormouse is protected by law because its numbers and distributional range have declined by at least 50% over the course of the last century, and continue to do so today.  This is primarily due to loss and fragmentation of woodland habitat as a result of forestry, urbanisation and agricultural practices.

Legislation

Dormice are given full protection under Schedule 5 of the Wildlife and Countryside Act 1981, as amended.  Protection to the species is also afforded by Schedule 2 of the Conservation (Natural Habitats &c) Regulations, 1994, making the hazel dormouse a European Protected Species.  These two pieces of legislation operate in parallel, although there are some small differences in scope and wording.  Under the provisions of Section 9 of the Wildlife & Countryside Act, it is an offence to:

  • Intentionally kill, injure or take a dormouse;
  • Possess or control and live or dead specimen or anything derived from a dormouse (unless it can be shown to have been legally acquired);
  • Intentionally or recklessly damage, destroy or obstruct access to any structure or place used for shelter or protection by a dormouse;
  • Intentionally or recklessly disturb a dormouse while it is occupying a structure or place which it uses for that purpose.

Schedule 2 of the Conservation (Natural Habitats &c) Regulations, 1994 make it an offence to:

  • Deliberately capture or kill a dormouse;
  • Deliberately disturb a dormouse;
  • Damage or destroy a breeding site or resting place of a dormouse;
  • Keep transport, sell or exchange, or offer for sale or exchange a live or dead dormouse or any part of a dormouse.

The dormouse is a Priority Species under the UK Biodiversity Action Plan (UK BAP), and has been adopted as a Species of Principal Importance in England under section 41 of the NERC Act 2006 (section 42 in Wales).

Licensing

A survey licence is required for checking nest tubes and dormouse boxes and for searching for dormouse nests where there is a risk of disturbing an occupied nest (e.g. by moving vegetation).  Survey licences are issued by the relevant Statutory Nature Conservation Organisation (Natural England or the Countryside Council for Wales). We employ ecologists who hold the necessary protected species licence to undertake dormouse surveys.

Additional licences or endorsements to standard licences are needed when marking dormice in any way (e.g. PIT tagging) or when collecting hair samples from live dormice for DNA analysis.

Survey

A dormouse survey would typically begin with a desktop search of available biological records to assess the likelihood of dormouse being present on site.  A walkover survey may then be completed to search for evidence of dormouse such as characteristically gnawed hazelnut shells (only possible where hazel trees are present) and dormouse nests in dense vegetation.

Dormouse population monitoring using nest boxes in Hastings

Dormouse population monitoring using nest boxes in Hastings

Frequently, however, where dormouse presence is considered likely, it will be necessary to conduct a nest tube survey to verify dormouse presence or absence from the site.  Typically a minimum of 50 nest tubes should be suspended along horizontal branches in suitable vegetation and checked thereafter for dormice and their characteristic nests. Nest tube surveys can be conducted any time during the dormouse active season (April-October), with each month being assigned an index of probability value of finding dormice.  The thoroughness of a survey (search effort score) is based on a calculation of index of probability values for the months surveyed and the number of nest tubes used.  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 nest tube

Dormouse nest

Mitigation & Compensation

The damage, disturbance and removal of dormouse habitat would typically need to be implemented under the auspices of a European Protected Species (EPS) licence issued by the relevant Statutory Nature Conservation Organisation (Natural England or Countryside Council for Wales). This will require appropriate mitigation to be implemented based on timing and undertaking habitat clearance in such a way as to minimise the risk of harm to dormice, their dependent young, and to hibernating individuals.  For small-scale habitat removal it may be possible to undertake vegetation clearance in one stage in May (if nesting birds are not an issue) or September-October, but for larger scale clearances, a two stage strategy may be more appropriate, with an initial winter cut of above-ground vegetation followed by full clearance over the period May to September.

Maintaining habitat continuity and connectivity are other factors that need to be taken into acount when planning a dormouse mitigation and compensation strategy – a process that can take a considerable amount of time, particularly in cases where planting is required that may not mature for several years.  Translocation of dormice to suitable off-site habitats is possible, but should be considered a last resort option as it is disruptive to natural populations, and suitable sites for releasing animals are often unavailable locally.

Applied Ecology Ltd have successfully obtained EPS dormouse licences on behalf of a number of developers across southern England.

See Survey Calendar for survey timings.

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