What happens in a bat survey?

If repair or alteration work is planned on a historic building, you may be told that a bat survey is required before work can begin. For many building owners this is unfamiliar territory. Understanding what a survey involves, who carries it out and how the results are used helps remove some of the uncertainty.

Bat surveys are a routine part of the planning and environmental process in England. Their purpose is simply to establish whether bats are using a building and, if so, how that use can be protected while building work proceeds.

Why bat surveys are carried out

Bats and their roosts are protected under UK wildlife legislation. Because of this, it is illegal to damage or disturb a roost without proper assessment and, where necessary, licensing.

When work is proposed on a building that might contain bat roosts — particularly roof repairs, loft conversions or structural alterations — planners or conservation advisers often ask for a survey to confirm whether bats are present.

The survey is not designed to stop work taking place. Its purpose is to gather information so that any necessary mitigation measures can be planned properly.

The first stage: a preliminary roost assessment

Most bat surveys begin with what is known as a Preliminary Roost Assessment (PRA).

This is usually carried out during daylight hours by a licensed ecologist. The surveyor inspects the building carefully, looking for signs that bats may be present.

Typical signs include:

• bat droppings

• staining around entry points

• small gaps used for access

• insect remains beneath roosts

• scratch marks or grease marks around openings
  

The surveyor will also assess the building’s potential suitability for bats. Even if no direct evidence is found, certain features may indicate that bats could be present.

Equipment used during a bat survey

Bat surveys do not usually involve heavy equipment. Most work is observational and relies on specialist ecological knowledge.

Common equipment used includes:

Bat detectors Electronic devices that convert ultrasonic bat calls into audible frequencies. These allow surveyors to identify bat activity during evening surveys.

Thermal cameras Sometimes used to detect bats leaving roosts at dusk.

Endoscopes or inspection cameras Small cameras used to look into cavities within roofs or walls.

Powerful torches Used to examine roof voids and crevices.

Ladders or access equipment Where safe access to roof spaces or elevations is required.

Surveyors may also use recording devices and data loggers to record bat calls for later analysis.

Activity surveys

If the preliminary inspection suggests bats may be present, further surveys may be required.

These are known as bat activity surveys or emergence surveys.

During these surveys ecologists observe the building at dusk or dawn to watch for bats entering or leaving the structure. Several survey visits may be required to gather reliable data.

Activity surveys normally take place between May and September, when bats are active. This can cause major delays in the planning process.

Why can’t you simply assume bats are present and design around them?

Building owners sometimes ask a sensible question: if bats are protected, why not simply assume they are present and carry out the work in a way that accommodates them?

In practice this approach rarely works for three reasons.

First, the law protects actual bat roosts, not hypothetical ones. Without a survey there is no evidence showing whether bats are present, which species may be involved or how the building is being used. Planning authorities and Natural England normally require documented evidence before approving mitigation measures.

Second, different bat species use buildings in different ways. Some use roof voids as maternity roosts during summer, others as winter hibernation sites, and some only use buildings occasionally. The mitigation required can vary significantly depending on how the roost is used, so simply installing a bat box or leaving a gap in the roof may not satisfy the legal requirements.

Third, licensing decisions rely on survey evidence. If work affects a confirmed roost, Natural England must be satisfied that appropriate mitigation is being provided. Without survey data the licensing authority cannot make that judgement, and permission may not be granted.

For these reasons planning authorities usually expect proper ecological surveys rather than assumptions, even where building owners are willing to take a cautious approach. A survey provides the evidence needed to ensure that repairs are lawful and that bats are properly protected.

Reports and documentation

Once surveys are completed, the ecologist prepares a written report.

This report normally includes:

• a description of the building

• survey methods used

• survey dates and weather conditions

• evidence of bat activity (if any)

• species identification where possible

• assessment of the building’s roost potential

• recommendations for mitigation if required

The report may also include drawings or photographs showing bat access points.

Forms and licensing

If bats are confirmed and work will affect the roost, a European Protected Species licence may be required.

In England these licences are issued by Natural England.

Licence applications normally include:

• the ecological survey report

• detailed mitigation proposals

• drawings showing how bat access will be retained or replaced

• a method statement for the works

The application is usually prepared by the licensed ecologist rather than the building owner.

Who gets notified?

Bat survey reports are usually submitted to the local planning authority as part of a planning application or Listed Building Consent application.

If a wildlife licence is required, Natural England will also review the documentation.

In some cases the planning authority’s ecology officer may review the report and recommend planning conditions to protect bats.

These conditions may require certain mitigation measures to be implemented during construction.

When surveys can take place

Different stages of bat surveys occur at different times of year.

Preliminary roost inspections can usually be carried out at any time of year.

However, activity surveys that observe bats entering or leaving buildings normally take place between late spring and early autumn when bats are active.

Because of this seasonal limitation, surveys can sometimes affect the timing of building projects.

Planning ahead is often the best way to avoid delays.

Can you carry out a bat survey yourself?

In theory anyone can look for obvious signs of bats in a building. However, surveys used for planning or licensing purposes must normally be carried out by a qualified ecologist.

Local authorities generally expect surveys to be prepared by experienced professionals with appropriate training.

A self-assessment by a building owner would rarely be accepted as evidence for planning purposes.

What qualifications do surveyors need?

Bat surveys used for planning or licensing purposes are normally carried out by licensed bat ecologists.

These specialists typically hold:

• a Natural England bat survey licence

• ecological qualifications or degrees

• professional membership of organisations such as the Chartered Institute of Ecology and Environmental Management (CIEEM)
  

Licensed ecologists are authorised to handle bats if necessary and to prepare licence applications where mitigation is required.

Using a qualified specialist ensures that surveys meet the standards expected by planning authorities and regulators.

Costs and timing

Bat surveys are usually modest in cost compared with most building projects.

Typical Midlands costs might include:

• preliminary roost inspection: £300–£600

• activity surveys: £600–£1,500 or more
  

If bats are present and licensing is required, additional costs may arise for mitigation measures or ecological supervision.

Timing can be more significant than cost. If surveys must take place during the summer activity season, work may need to be scheduled accordingly.

The practical reality

Although bat legislation can appear intimidating, surveys are now a routine part of the planning process.

In many cases surveys simply confirm that bats are not present, allowing work to proceed without difficulty.

Where bats are present, sensible mitigation measures usually allow repairs or alterations to proceed while protecting the roost.

With the right advice and early planning, bat surveys are simply another step in the process of caring for historic buildings responsibly.