Dormouse Survey

Dormice are typically found in woodland, hedgerows, and scrub habitats throughout much of southern and central Britain, though populations are often scattered and at low density. Since 2000, the UK population has declined by over a half (51%), decreasing on average by 3.8% per year. They are fully protected under UK and European law, making it an offence of kill, capture, or disturb them, or to damage their habitat. Appropriate survey licences are required to work with this species. 

​

The appraisal is used to establish the presence/ likely absence and distribution of dormice on site, informing the emerging scheme design, and enabling significant ecological effects within the zone of influence to be avoided, mitigated, or compensated for, where necessary. This ensures the continued favourable conservation status of dormice, post development, and ultimately compliance with nature conservation legislation and planning policy. 

​

There are three types of dormouse survey, comprising site suitability appraisals, nut searches, and nest tube/ box surveys. Site suitability appraisals involve assessing the potential of habitats to be used by dormice, generally based on three indices: vegetation composition (species diversity); vegetation structure; and ecological connectivity to the wider landscape.

 

Nut searches involve physical searches for hazel nuts, showing the characteristic signs of gnawing by dormice. Typically, this involves the sampling of three 10m x 10m areas of heavily fruiting hazel. This methodology is rarely sufficient to provide a high level of confidence regarding likely absence, though positive identification of nuts processed by dormice provides instant confirmation of presence, expediting the survey process.

 

Presence/ likely absence surveys are based on an index of probability scoring system, where different months within the survey season entail varying likelihoods of dormice being detected, consequently eliciting different index probability scores for each month. Artificial nest tubes or boxes are deployed throughout suitable habitats, and inspected over several months throughout the survey period. A survey index score of at least 20 points is required to assume likely absence. The field survey is typically supplemented by a desk study, utilising maps and aerial photographs of the surrounding area to identify ecological connectivity, and published records of dormice, purchased from the local records centre.

 

Requirements for any necessary avoidance, mitigation, or compensation measures will be identified, and opportunities for ecological enhancement will be outlined, to integrate on-site biodiversity net gain into the scheme at an early stage, where possible.​ If the proposals are deemed likely to adversely affect dormice, a European protected species mitigation licence may be required, prior to the commencement of works.

 

Dormouse surveys are seasonally constrained and protracted, making it prudent to plan ahead and consider ecological issues early on in the planning process. A robust dormouse survey at an early stage in project planning and design can therefore deliver significant benefits, avoiding potentially costly and time-consuming delays.​

 

When

 

Site suitability appraisals can be undertaken throughout the year, as can nut searches, though the optimal season (when nuts are yet to deteriorate to the extent that identification of the characteristic marks becomes difficult) lies between mid August-December inclusive. Dormouse presence/ likely absence surveys can be undertaken between April-November inclusive.