A bat survey will determine what species of bat are present, estimate numbers of bats, find bat access points, and assess how and when bats are using the building. Finding bats is a skilled operation and building owners or managers will need to commission a bat specialist consultant licensed by Natural England.
Do you need to do a bat survey?
Thorough planning and realistic timescales are essential when undertaking building works, but this is never more so than when they involve buildings with bats.
When taken into account, bats do not prevent building works from going ahead or delay them, but discovering bats when works have started could cause expensive delays to your work and may lead to prosecution. Early involvement of a bat specialist allows for bats to be accounted for in the project design, schedule and budget – so no unexpected surprises!
The best strategy is to be proactive and get surveys commissioned so that when works are required, you already have the information you need. For instance, when carrying out periodic condition surveys to inform maintenance and future repair works, include a regular bat survey too. Generally Natural England will expect survey data for licence applications to be less than two seasons old.
Even minor maintenance works could affect bats or their roosts. If there have been no recent or regular surveys of bats at the property, you should seek advice and commission a survey before planning works on structures such as:
- Roofs or roof voids (including repairs and re-roofing, painting or replacing barge boards/soffits/guttering, insulation or boarding, adding fire walls, chimney repairs/capping/lining, re-wiring and plumbing, timber treatment or pest control)
- Walls (including re-pointing and grouting, removing loose render or plaster, wall cavities, replacement or repair of shingles, hanging tiles or weatherboarding)
- Doors and windows (including repairing, re-glazing, painting, timber treatment, replacing frames, doors or windows)
- Cellars and other underground sites (including repairs, wiring and plumbing, safety works, lining and sub-dividing spaces)
The local planning authority is likely to require a bat survey. Many authorities publish biodiversity checklists to guide you on what expert ecological advice will be needed before submitting a planning application. The Biodiversity in Planning partnership also provides a useful free online tool for householders and small to medium-scale developers.
A bat survey is likely to be required for historic sites if works involve:
- Conversion, modification, restoration or demolition of buildings which are:
- Traditional constructed farm buildings with exposed wooden beams
- Weather boarded or tile hung buildings near woodland or water
- Pre-1960 detached buildings near woodland or water
- Pre-1914 buildings with gable ends, or slate roofs
- Other buildings adjacent to woodland or water
- Dutch barns and livestock buildings with a single skin roof and boarding
- Development affecting built structures such as tunnels, bridges, mines, kilns and industrial chimneys, ice-houses, military fortifications, air-raid shelters, cellars and so on
- Floodlighting of buildings and sites close to woodland, water, field hedgerows or lines of trees connecting to other woodland or water
- Felling, removal or lopping of woodland, hedgerows, old and veteran trees, and mature and dead trees with obvious holes and cavities, or covered with ivy
- The Bat Conservation Trust provides more detailed guidance.
Where horseshoe bats are found (mainly south-west England and Wales), additional information on surrounding roosts and flight lines may be required by Natural England as they are listed on Annex II of the Habitats Directive for their conservation significance. This also applies to barbastelle and Bechstein's bats. These two species usually roost in trees, although barbastelles are also often found in old buildings.
If the habitats around the building will be disturbed either by vegetation removal or the addition of lighting, you will also need to take this into account and may need to undertake a wider bat activity survey of the area.
Timing of bat surveys
Timing is paramount and the licensed bat specialist consultant will know the best times of year to find signs, to see bats and to judge the number of bats present.
As bats often roost in inaccessible crevices there may be no obvious signs of their presence on the outside of a building. Therefore, it is likely to be necessary for a bat specialist to conduct a daytime preliminary roost assessment followed by further surveys to establish if bats are present, their species, numbers and roost type.
Initial roost inspection surveys on buildings can be carried out at any time of year, however, surveys that require bats to be active, such as detection of maternity roosts during the summer, are carried out from May to August.
For these emergence and re-entry surveys, the surveyors watch for bats leaving the building or returning at dusk or dawn. Across the UK demand for bat specialist consultants during the summer activity period is high so you will need to book survey work well ahead.
Weather conditions on the days of the emergence/re-entry surveys are an important factor as they can influence results. Poor weather such as high winds or heavy rain may result in surveys having to be rescheduled and these issues will need to be factored in the project planning.
The following link shows a table of the recommended months for different survey types:
Arranging a bat survey
Bat surveys require specialist knowledge and equipment, and only those with the appropriate bat licence may enter a bat roost as this could cause disturbance.
The Chartered Institute for Ecology and Environmental Management (CIEEM) provides searchable directories of bat specialist consultants. For minor works to homes and churches which seem unlikely to need a licence, you can ask the Bat Conservation Trust to arrange for a local licensed volunteer bat specialist to assess the situation and provide initial advice.
The Bat Conservation Trust also provides advice about appointing a bat specialist consultant to undertake a survey. All bat surveys should be carried out in accordance with the Bat Conservation Trust’s Bat Surveys for Professional Ecologists: Good Practice Guidelines (4th edition, 2023). This publication provides detailed guidance on designing and undertaking bat surveys, data analysis and survey reports. The aim of these guidelines is to improve consistency and to develop a greater understanding of bats, and how to protect them.
Insurance for bat specialists
As a minimum, bat specialists, whether voluntary or paid, will have public liability insurance (typically at £5 million). Bat specialist consultants should also hold professional indemnity insurance. Professional indemnity cover depends on the scale of the work that the bat worker typically takes on and may vary from, say, around £250,000 offered by an individual to £5 million-plus offered by consultancy firms. You will need to ask the person you contract what their insurance cover is and decide whether it is appropriate for the job you are asking them to do.
Briefing the bat specialist consultant
The bat specialist consultant will need to be briefed about any designations such as listing and also historically important features such as decorations, and conservation or building management concerns/problems (if any) caused by bats.
The consultant will need a building plan marked with roof voids, chimney stack and room numbers or names. If the survey is being undertaken for specific planned work, the consultant will also need to know the type and extent of works planned and the proposed timings for the work.
A building or work site must be safe for the consultant to enter and survey. Risk assessments must be carried out and the bat surveyor notified ahead of any unsafe areas and hazards, or significant historic collections or artefacts. The risk assessment may need to consider:
- Handling bats
- Lone working
- Working in enclosed spaces
- Working at night
- Working at height
For further advice:
- See Appendix 3 of Bat Surveys for Professional Ecologists: Good Practice Guidelines (2016)
- Mitchell-Jones, A J and McLeish, A P 2012 The Bat Workers’ Manual. Exeter: Pelagic Publishing
- Health and Safety Executive (HSE)
- If you are carrying out work for an organisation like the National Trust or the English Heritage Trust, it may have its own generic and specific risk assessments.
The bat survey report
The bat survey report should include photos, plans and/or sketches that clearly identify potential and confirmed bat access points, potential and confirmed bat roost sites, and details regarding droppings and other evidence of bats.
Before carrying out the survey, the bat specialist consultant should have sought historic bat records from the Local Environmental Records Centre, searched for any previous survey reports, and talked to people familiar with the building, such as an owner/occupant, and the architect/conservator. This information will be needed for a bat mitigation licence if required.
Advice on bat survey reports is included in Chapter 11 of Bat Surveys for Professional Ecologists: Good Practice Guidelines (2016).
The bat specialist consultant will propose an acceptable scheme of work that will avoid committing any offences, including details on project layout and timings of building works to avoid impacts in the first instance. The bat specialist consultant and conservator need to collaborate to ensure possible solutions for the bats don’t undermine the conservation of the building, its historic features, fittings and decorations.
If the consultant judges that a licence application will be necessary, their report will include the required licence method statement that gives details of a proposed scheme of works and proposals for mitigation to avoid adverse impacts on the bats present.