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Dormice (Muscardinus avellanarius) are about the same size as other mice (weight 17-20g, but can weigh up to 30-40g just before hibernation. Their head-body length is 6–9cm, with tail length 5.5–8cm. It is one of our most recognisable small rodents because of its golden fur, furry tail and large black eyes.
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Dormice (Muscardinus avellanarius) are about the same size as other mice (weight 17-20g, but can weigh up to 30-40g just before hibernation. Their head-body length is 6–9cm, with tail length 5.5–8cm. It is one of our most recognisable small rodents because of its golden fur, furry tail and large black eyes.

Dormice, uniquely amongst smaller mammals in Britain hibernate over winter (October – Late April) surviving on fat laid down the previous autumn. They hibernate in closed woven nests, often at the base of tree stumps, under log piles, under moss or leaf litter where there is stable humidity and temperature.

During summer, dormice build nests in tree cavities or in shrubs. Nests are usually woven from shredded honeysuckle bark or, if this is not available, grasses or leaves.

When active dormice are nocturnal (awake at night) and arboreal (e.g. feeds in the branches of trees and shrubs). They are reluctant to cross open ground so can easily become isolated due to habitat loss.

Dormice are most commonly found in deciduous woodland and scrub, particularly mixed hazel coppice woodland which provides a varied diet throughout the year. However dormice are also found in other scrub and hedgerow habitats, and even conifer plantations.

Dormice have specific feeding requirements. They do not live in large numbers at any one site and are not able to easily move to new sites. They are also very sensitive to changes in their habitat and the climate.

Guidance Note 1:

It is the responsibility of the organisation or individual wishing to carry out the development to make sure that they comply with the law.


Dormice and their breeding sites and places of shelter receive full statutory protection under the Wildlife and Countryside Act 1981 (as amended) and the Conservation of Habitats and Species Regulations 2010 (as amended) (the Habitats Regulations). This makes it an offence to kill (or injure), take or disturb any dormouse or damage or disturb any breeding site or place of shelter.

The combined effect of the national and European legislation is to afford full protection to dormice, their breeding sites and resting places. Without a licence it is an offence for anyone to deliberately disturb, capture, injure or kill them. It is also an offence to damage or destroy their breeding or resting places, to disturb or obstruct access to any place used by them for shelter. It is also an offence to possess, or sell a wild dormouse.

It is extremely important that developers and landowners wishing to undertake activities that may affect dormice obtain site-specific advice before formulating their designs and programme.

Any development proposal or activity that would impact on dormice or any of their habitats is required to provide for conservation of the species and its habitats under licence from Natural Resources Wales.

If the proposed activity requires planning consent, or any other type of consent (e.g. listed building consent, extraction licence, etc.), this consent must be in place and provided to Natural Resources Wales with the licence application.

Developers and landowners should note that a licence is often required from Natural Resources Wales (NRW) to carry out development and vegetation clearance works that affect dormice (and any other European protected species), irrespective of whether planning permission is required to undertake those works. Failing to secure a licence before starting development or site clearance works could result in an offence(s) being committed. This could lead to delay, prosecution, fines, confiscation of equipment, legal fees and, potentially, a custodial sentence.

A licence is granted under the provisions set out in the Habitats Regulations. In order to grant a licence, NRW must be satisfied that the proposed activity meets the criteria in the Habitats Regulations, often referred to as “the three tests”.

These tests include:

  • the need for the proposed development/activity;
  • consideration of possible alternatives (e.g. activity, method, timing, phasing, location etc.);
  • maintaining the favourable conservation status of the population of dormice to be affected.

The Habitats Regulations imposes a similar duty on Bridgend County Borough Council to consider the impact of a proposed development on dormice before determining planning applications that could affect the species or their habitats. The Council must therefore also be satisfied that the proposals will meet the criteria of the three tests set out in the Habitats Regulations in order to grant planning consent. This duty is irrespective of whether the application is for outline, reserved matters or full planning.

In order to assist the Council and NRW (if a licence is required) assess proposals, the developer or landowner must provide sufficient information to make the determination against the Habitats Regulations, including:

  • up to date presence / absence survey data;
  • population estimate, if present;
  • habitat assessment;
  • impact assessment;
  • mitigation and compensation strategy;
  • management and monitoring plan.


The maximum penalty for non-compliance with the above legislation for each offence is a £5000 fine and/or six months imprisonment. Any equipment used to commit the offence may be forfeited. Both the company and the individuals can be held liable.



If there are woodlands or areas ofspecies rich scrub within the boundary of the development site and/or there are existing dormice records on or within 500m of the boundary of the development site, the Council will require a dormice survey. This survey needs to be undertaken by a suitably experienced and qualified ecologist.

Dormice can be affected by a range of activities including hedgerow work, road schemes, housing developments or woodland operations

Dormice occur in a wide variety of woody habitats, ranging from ancient semi-natural woodlands with hazel coppice and standard oaks, to species-rich scrub. They are
also increasingly reported living in hedgerows, areas of plantation conifers and rural gardens. They may even be found in a range of habitats close to woodland therefore, their absence should not be assumed simply on the basis of a ‘nontypical’ habitat.

When suitable habitat occurs on or within 500m of a site, a records search should be undertaken to identify any previously identified dormice populations in the local area. The search for records should be made to at least 500m from the proposal site, sometimes further depending on the scale of development, likely impacts and whether a landscape scale population assessment approach may be beneficial.

Dormice can be found in species rich scrub and some rural gardens.

The South East Wales Biological Records Centre should be requested to undertake a search. In addition other relevant organisations may hold useful data including National Biodiversity Network, NRW, and the local wildlife trust.

If no records of dormice are present within 500m of the development site or survey(s) do not confirm” presence of dormice, but there is suitable habitat on and adjacent to the development, site developers should also make reference to guidance sheets relating to species that may also occur in that habitat.

Survey Methodology

GUIDANCE NOTE 3: The Council will only accept survey/assessment work which has been undertaken by a suitably qualified person within the recognised survey guidelines.

General survey guidance for protected species can be found in Guidance Sheet B9: Survey Requirements. In addition The Dormouse Conservation Handbook and the Interim Natural England Advice Note - Dormouse surveys for mitigation licensing - best practice and common misconceptions provide detailed guidance for surveying dormice.

The appointed ecologist should make an assessment of any suitable habitat on or near the site (within around 500m provided that they are not separated by significant barriers to dispersal such as a major trunk road or motorway).

The best hedgerows for dormice are wide and tall with abundant mast and fruit-bearing trees and shrubs.

Preliminary surveys should normally be undertaken to detect actual presence or demonstrate likely absence.


Planning surveys at an early stage will reduce potential cost and delays were dormice to be discovered during works on a site that had not been surveyed.

No area of woodland should be presumed to lack dormice, except very small unsuitable copses of less than 10 ha in extent which have poor habitat and are separated by at least 500 m from the nearest suitable habitat.

However, since dormice are known to occur in some types of amenity woodland, conifer plantations and scrub, as well as deciduous forest, the survey process should not be eliminated solely on the grounds that the habitat is ‘unsuitable’.

Dormouse surveys to support a mitigation licence application should employ sufficient survey effort to determine presence/likely absence of the species on site. The survey effort required should be tailored to the site specifics, which will change on a case by case basis. This should be used alongside habitat survey data for the site and published research to provide an estimate of the population that will be impacted by the works, which is required for the licence.

For higher impact cases it is likely to be necessary to determine whether breeding is occurring on site and intensive survey effort prior to impacts will allow more meaningful comparison as part of a monitoring package following completion of works.

Dormice are usually active from April to October, exact timings will vary from year to year, dependant on location within the UK, weather conditions and available food resources. Surveys should aim to cover months with the highest probability of detecting dormice. Ideally nest tube surveys should be planned to start early in the active season, to cover the first peak in tube use. Nut surveys should usually be employed in the time period from September to December, beyond this time nuts may lose their diagnostic characteristics, dependant on ground conditions.


Where surveys indicate that dormice will be affected by the development proposal, the Council will require a Method Statement to be submitted with the planning application for the application to be registered. If it is considered that the proposed avoidance, mitigation, compensation measures are not satisfactory, the Local Planning Authority will refuse the planning application.

The data obtained from the dormice surveys must be formulated into a Method Statement which is submitted to the Council to inform their planning decision.

A Method Statement which follows mitigation and survey guidance within The Dormouse Conservation Handbook (second edition) alongside published papers will enhance the likelihood of your application being acceptable. Deviations from the recommendations contained within this handbook should be justified within the Method Statement.

The impact assessment should be presented in the Method Statement. Impacts should be classified as temporary, short term or long-term and the scale of each impact should be identified. The Method Statement should include practical avoidance measures and, where avoidance is not possible, provide a detailed mitigation strategy, including a timetable.

The Method Statement should also identify whether a licence is required prior to commencing development activities.

Developers and landowners should note that the Council will not condition the production of the Method Statement. The information in the Method Statement is required to assist the Council to make their determination in regards of the Habitats Regulations. Applications in which an effect upon dormice is anticipated as a result of the proposals, but which do not include an appropriate Method Statement will most likely not be validated.

If the application is validated, but the information relating to dormice is subsequently found to be insufficient during the determination, this may affect the result of the planning decision.


NRW has a standard method of application for licences in respect of development. Briefly, a licence application requires the developer or landowner who will be undertaking the proposed works to appoint a suitably qualified and experienced ecologist who will be named on the licence application. The appointed ecologist will most likely be responsible for coordinating the licence application, which requires the completion of an application form and a Method Statement. The Method Statement must be to the approved NRW format (provided with the licence application information) and will present much the same information as that required by the Council to inform the planning application. Licence applications normally take up to 30 days for a determination.

The licence granted will have conditions attached and will only be valid with the approved Method Statement. The licence permits only those activities identified in the Method Statement, so it is important that developers and landowners carefully review and agree the Method Statement before submission.

The activities and measures detailed in a licence are there to avoid unnecessary harm to the protected species. Failure to follow the exact measures in the licence can lead to prosecution. Any activity carried out that deviates significantly from the licensed Method Statement may be considered a breach of the licence. This includes works carried out in different locations, using different methods or at a different time than that identified in the Method Statement. Any committed works identified in the Method Statement, such as inspecting and maintaining exclusion fencing, carrying out monitoring and management works or mitigation measures being supervised on site by the ecologist, which are not implemented as specified in the licensed Method Statement might also be considered a breach of the licence.

A breach of the licence is considered to be a criminal offence. Under the current legislation (see penalties above), anyone authorised to carry out activities implemented under the licence may be held responsible for breaches of the licence terms and conditions. It is therefore important that all staff and contractors on the site are fully briefed on the licence and its implications for working on site, prior to being allowed to start on site. An up to date copy of the licence and the associated Method Statement should be held on site at all times, together with any identification sheets that may be helpful to site workers and contact details for the appointed ecologist.

Licences have an expiry date. If works need to continue beyond the expiry date an extension must be applied for. An extension cannot be issued for a licence that has expired, once a licence has expired then a new licence must be applied for. Depending on the time elapsed from expiry this may or may not require additional surveys to ensure that accurate and up to date information supports the licence application.



Developers/applicants must providesufficient evidence to demonstrate that avoidance is not possible before mitigation or compensation is considered as a viable alternative.

Avoidance measures built into development proposals may remove the need for detailed survey work, the council will seek expert advice from NRW in determining cases when this may be applicable.

Avoidance measures are those measures that can reasonably be implemented to avoid an offence occurring. As such, these Reasonable Avoidance Measures (RAMs) can often avoid the requirement for a licence. RAMs are the preferred approach when considering design of a scheme. RAMs may include measures ranging from revising the site layout to avoid loss of an important feature, carrying out works at a time which is less likely to result in disturbance or amending working methods to reduce impacts to an acceptable level.

If RAMs are practical within a scheme, these must still be detailed in a Method Statement which is submitted to the Council for approval. Implementation of the measures outlined in the RAMs Method Statement will likely be a condition of the resulting planning consent.

If the RAMs avoid all anticipated impacts affecting dormice and their habitats to acceptable levels, a licence is unlikely to be required. This can often avoid or reduce delays to commencing development and will often reduce costs as well. It is therefore important to create communication channels between your architects (landscape or otherwise) and your chosen suitably qualified ecologist during the masterplanning process. This will aid in guiding the design and programme at an early enough stage to identify whether RAMs may be a suitable approach.

Early identification and incorporation of green infrastructure assets e.g. hedgerows, trees, ponds into a development will help reduce the development impact of a scheme and provide opportunities for RAMs and avoid more complex mitigation and compensation schemes which may require a license.

For example: retention of a dormice habitat into the design of a development, with a suitable vegetation buffer with connectivity to suitable woodland may be able to demonstrate avoidance of impact of the development on dormice. The planting of hedgerows, woodland blocks for improved connectivity may result in net benefit.



Where RAMs cannot satisfactorily avoid impacts affecting dormice, mitigation measures will be required to ensure no harm comes to dormice and that no net loss of their habitats results.

Mitigation guidelines and additional information for dormice can be found on the Natural England website.

Depending on the scale of development and predicted impacts, it may not be possible to rely on RAMs alone to fully address all potential impacts affecting Dormice or their habitats. Early communication across the design team will promote a greater understanding of all the constraints, ecological or otherwise, and allow a balanced approach to the development design.

The exact measures required will be dependent on the population size, distribution and proximity to works and the scale, timing and duration of the works.

Mitigation measures to be implemented will be detailed in the Method Statement and will be licensed activities and must therefore be carried out in strict accordance with the Method Statement.

Mitigation should aim to ensure that the population will be free from further disturbance, and will be subject to adequate management, maintenance and monitoring.



Compensation will only be considered where the developer/applicant has satisfactorily demonstrated that avoidance and mitigation are not possible and the compensatory measures result in no net loss of habitat.

Where mitigation cannot satisfactorily reduce all potential impacts to satisfactory levels, additional compensation measures will likely be required. Compensation measures will be requirements of the licence. All compensation measures outlined in the licence must be adhered to; failure to do so constitutes a criminal offence.

Compensation guidelines and additional information for dormice can be found on the Natural England website. 

Compensation measures should ensure that the affected dormouse population can function as before. The reasoning behind this concept is that the acceptability of newly created habitat to dormice is not predictable. In addition, not all the new habitat may be immediately available due to the time it takes for planted shrubs and trees to bear fruits and flowers.

Compensation measures most frequently involve habitat losses. For example, if the loss of woodland cannot be avoided in the proposed development then a compensatory woodland should be created prior to the loss, in accordance with the licence requirements. For loss of dormice habitat, a greater amount of habitat must be created to compensate the loss to maintain breeding, foraging, refuge and dispersal functions for the affected population. The population size and natural range must also be maintained, so it will be important to consider the connectivity between retained habitats, new habitats and existing habitats in the wider area. 

It must be recognised that ancient woodland is irreplaceable.

Habitat compensation must be provided in advance of persuasion or translocation methodologies. This will allow dormice and other fauna to move into the compensation area(s) before they are disturbed by development.


Large development sites have the opportunity to enhance the surrounding habitats and connecting corridors for dormice and other flora and fauna and provide natural interest for residents.

  • Incorporation of native species woodlands and hedgerows into new developments, even if dormice are not affected by the development.
  • Where dormice are affected, a greater amount of habitat must be created to compensate the loss Creation of ‘networks’ will help link areas of suitable terrestrial habitat;
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