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Development advice

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

Uniquely amongst smaller mammals in Britain, dormice hibernate between October and late April by surviving on fat laid down the previous autumn. They hibernate in closed woven nests often at tree stump bases, under log piles, under moss or leaf litter where humidity and temperatures are stable.

In summer, dormice build nests in tree cavities or shrubs. Nests are usually woven from shredded honeysuckle bark, or, if this is unavailable, grasses or leaves.

When active, dormice are nocturnal and arboreal, feeding in the branches of trees and shrubs. They are reluctant to cross open ground and so can easily become isolated due to habitat loss.

Most commonly, dormice are found in deciduous woodland and scrub. In particular they are found in 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 unable to move easily to new sites. Also, they are very sensitive to changes in their habitat and the climate.

Guidance note one:

It is the responsibility of the organisation or individual wishing to undertake the development to ensure they comply with the law.

It is an offence to kill or injure, take or disturb any dormouse or damage or disturb any breeding site or place of shelter. Dormice and their breeding sites and places of shelter have full statutory protection under:

The combined effect of the national and European legislation is to give dormice, their breeding sites and resting places full protection. Without a licence, it is an offence for anyone to deliberately disturb, capture, injure, or kill them. Also, it is an offence to damage or destroy their breeding or resting places, or disturb or obstruct access to their sheltering places. Further it is an offence to possess, or sell a wild dormouse.

Developers and landowners planning activities that may affect dormice should take site-specific advice before developing designs and a programme. Any development proposal or activity affecting dormice or their habitats must provide for the species’ and its habitats’ conservation under licence from Natural Resources Wales.

If the proposed activity needs planning consent, it must be in place and provided to Natural Resources Wales (NRW) with the licence application. It may include content like listed building consent, or extraction licences.

A licence is often needed from NRW to undertake development and vegetation clearance works affecting dormice or any other European protected species. This is irrespective of whether planning permission is needed to do those works. Failing to get a licence before starting development or site clearance could result in offences 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 Habitats Regulations provisions. To grant a licence, NRW must be satisfied that the proposed activity meets the Habitats Regulations’ criteria which are referred to as “the three tests”.

The three tests

These tests consider:

  • the need for the proposed development/activity
  • possible alternatives to factors like activity, method, timing, phasing, location
  • maintaining the good conservation status of the dormouse population to be affected

Similarly, the Habitats Regulations require us to consider a proposed development’s affect on dormice before determining planning applications that could affect them or their habitats. Therefore we must also be satisfied that proposals meet the three tests’ criteria as the Habitats Regulations set out in order to grant planning consent. This duty is irrespective of whether the application is for outline, reserved matters or full planning.

To help us and the NRW assess proposals, developers or landowners must give enough information to make the determination against the Habitats Regulations. This includes:

  • up to date presence or absence survey data
  • a population estimate, if present
  • a habitat assessment
  • an impact assessment
  • a mitigation and compensation strategy
  • a 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 companies and individuals can be held liable.

Guidance note two:

We require dormice surveys where there:

  • are woodlands or areas of species-rich scrub within the development site boundary
  • are existing dormice records on or within 500m of the boundary of the development site

This survey must be run by a suitably experienced and qualified ecologist.

Dormice can be affected by several activities including hedgerow work, road schemes, housing developments or woodland operations.

They live in a wide variety of woody habitats, ranging from ancient semi-natural woodlands with hazel coppice and standard oaks, to species-rich scrub. Increasingly, dormice are reported living in hedgerows, areas of conifer plantation and rural gardens. They may even be found in diverse habitats close to woodland and so, their absence should not be assumed simply due to ‘nontypical’ habitats.

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

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

Site developers should also refer to guidance sheets relating to species that may also be in that habitat if:

  • there is no record of dormice present within 500m of the development site
  • surveys do not confirm dormice’s presence, but there is suitable habitat on and adjacent to the development

Guidance note three:

We will only accept survey/assessment work which has been done 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’. Also detailed guidance for surveying dormice is found in:

The appointed ecologist should make an assessment of any suitable habitat on or near the site. This would be within around 500m provided that it is 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.

Normally preliminary surveys should be run to detect any actual presence or show the species’ likely absence.

Guidance note four:

Planning surveys at an early stage reduces potential cost and delays should dormice be discovered during works on a site which had not been surveyed.

No woodland areas should be presumed to lack dormice. That is except for unsuitable copses below 10 hectares in extent with poor habitat and separated from the nearest suitable habitat by at least 500m.

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

Dormouse surveys to support a mitigation licence application should use enough survey effort to determine the presence/likely absence of the species. Tailor the survey effort to the site specifics, which will change on a case by case basis. Use this alongside the site’s habitat survey data and published research to give an estimate of the population to be affected, which the licence requires.

For higher impact cases, it is likely necessary to determine whether breeding is happening onsite. Intensive survey effort before changes will allow a more meaningful comparison as part of a monitoring package after the works end.

Dormice are usually active from April to October. However exact timings will vary annually depending on the site’s location in 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 occur from September to December, as beyond then nuts may lose their diagnostic characteristics depending on ground conditions.

Guidance note five:

Where surveys show the development proposal will affect dormice, we will need a method statement submitted with the planning application before it is registered. If it is considered that the proposed avoidance, mitigation, and compensation measures are unsatisfactory, the Local Planning Authority will refuse the planning application.

The dormice surveys’ data must be developed into a method statement which is sent to us to inform our planning decision.

A method statement following mitigation and survey guidance in The Dormouse Conservation Handbook (second edition) alongside published papers will boost your application’s chances of success. Deviations from the handbook’s recommendations should be justified in the method statement.

Present the impact assessment in the method statement. Impacts should be classified as temporary, short term or long-term and the scale of each should be identified. The method statement should include practical avoidance measures, and, where avoidance is impossible, provide a detailed mitigation strategy including a timetable.

The method statement should also identify whether a licence is needed before starting development activities.

Developers and landowners should note that we will not condition the production of the method statement. The information in the method statement is needed to help us make our determination regarding the Habitats Regulations. Applications which anticipate an effect on dormice due to the proposals, but which do not have an appropriate method statement will probably not be validated.

If the application is validated but the information relating to dormice is later found insufficient during the determination, this may affect the planning decision’s result.

NRW has a standard method of application for licences regarding development. Briefly, a licence application needs the developer or landowner who will be undertaking the proposed works to appoint a suitably qualified and experienced ecologist. Name the latter on the licence application. The appointed ecologist will most likely be responsible for coordinating the licence application, which requires a completed application form and a method statement.

The method statement must be to NRW’s approved format as provided with the licence application information. It will present much the same information as we need 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 the method statement notes. Thus 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 licence’s exact measures 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 the method statement identifies which are not implemented as the specified might also be considered a breach of licence. These may include inspecting and maintaining exclusion fencing, carrying out monitoring and management works or mitigation measures being supervised on site by the ecologist.

Breaching the licence is a criminal offence. Under the current legislation, anyone authorised to enact activities implemented under the licence may be held responsible for breaches of its terms and conditions. See the penalties above under ‘legislation’.

Therefore it is important that onsite staff and contractors are fully briefed on the licence and its implications for working onsite before starting onsite. An up to date copy of the licence and the associated method statement should be held onsite at all times. Also, any identification sheets that may be helpful to site workers and contact details for the appointed ecologist should be onsite.

Licences have an expiry date. If works need to continue beyond the expiry date, an extension must be applied for, and an extension cannot be issued for a licence that has expired. Once a licence has expired, a new licence must be applied for. Depending on the time since expiration, this may or may not require extra surveys to ensure accurate information supports the licence application.

Guidance note six:

Developers/applicants must give sufficient evidence to demonstrate that avoidance is impossible before mitigation or compensation is considered a viable alternative.

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

Avoidance measures are those which can reasonably be implemented to avoid offences occurring. As such, these Reasonable Avoidance Measures (RAMs) can often avoid the need for a licence. RAMs are the preferred approach when considering a scheme’s design. 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
  • 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 sent to us for approval. Implementing the measures outlined in the RAMs method statement will likely be a condition of the resulting planning consent.

If the RAMs avert all anticipated impacts on dormice and their habitats to acceptable levels, a licence is unlikely to be needed. This can often avoid or reduce delays to commencing development, and will often reduce costs as well. Therefore, it is important to create communication channels between your architects whether landscape or otherwise and your chosen suitably qualified ecologist during the masterplanning process. This will help to guide 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 such as hedgerows, trees, and ponds into a development will help reduce a scheme’s development impact. It provides opportunities for RAMs, and avoids more complex mitigation and compensation schemes which may need a license.

For example, retaining dormouse habitat in a development’s design with a suitable vegetation buffer and with connectivity to suitable woodland could show avoidance of impact. Planting hedgerows and woodland blocks for improved connectivity may create a net benefit.

Guidance note seven:

Where RAMs cannot satisfactorily avoid affecting dormice, mitigation measures must ensure dormice are unharmed with no net loss of their habitats.

The Natural England website gives mitigation guidelines and additional information for dormice.

Depending on the scale of development and predicted effects, it may be impossible to rely on RAMs alone to fully address all potential impacts on dormice or their habitats. Early communication amongst design teams promotes a greater understanding of the constraints whether ecological or otherwise, and allows a balanced approach to development design.

The exact measures needed will depend on population size, distribution and proximity to works and the works’ scale, timing and duration.

The method statement will detail mitigation measures for implementation, which will be licensed activities. Therefore, they must 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.

Guidance note eight:

Compensation will only be considered where the developer/applicant satisfactorily demonstrates avoidance and mitigation are impossible and the compensatory measures result in no net habitat loss.

Where mitigation cannot reduce all potential impacts to satisfactory levels, additional compensation measures will likely be needed. The licence will require compensation measures. All compensation measures the licence outlines must be adhered to, and failure to do so constitutes a criminal offence.

The Natural England website gives compensation guidelines and additional information about dormice. Compensation measures should ensure that the affected dormouse population can function as before. The reasoning behind this is that the acceptability of newly created habitat to dormice is unpredictable. Also, not all the new habitat may be immediately available due to the time taken for planted shrubs and trees to blossom and fruit.

Compensation measures most frequently involve habitat losses. For example if the proposed development cannot avoid losing woodland, a compensatory woodland should be created before the loss, as per the licence requirements. For loss of dormouse habitat, more habitat must be created in compensation to maintain breeding, foraging, refuge and dispersal functions for the affected population. Also the population size and natural range must be maintained. Thus 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 ahead of persuasion or translocation methods. This will allow dormice and other fauna to move into compensation areas before they are disturbed by development.

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

Enhancements includes:

  • incorporating native species of woodlands and hedgerows into new developments, even if the development does not affect dormice
  • creating a greater amount of habitat to compensate the loss where dormice are affected
  • creating ‘networks’ to help link areas of suitable terrestrial habitat

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