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Bat Emergence Surveys for Planning Applications: Requirements, Timing & FAQs

 

Bat emergence surveys are commonly required to support planning applications where development proposals may affect buildings, bridges, or other structures with potential to support roosting bats.

These surveys are typically requested by Local Planning Authorities following a Preliminary Bat Roost Assessment (PBRA), where bat roosting potential or evidence of bats has been identified.

This article explains:

  • When bat emergence surveys are required
  • How many surveys are needed
  • Seasonal timing constraints
  • What happens if bats are found
  • How long survey data remains valid

Bat Survey Guidelines

For planning authorities to accept bat surveys as sufficient to inform determination of a planning application, surveys are generally expected to comply with the current best practice guidance:

Collins, J. (ed.) (2023) Bat Surveys for Professional Ecologists: Good Practice Guidelines (4th Edition), Bat Conservation Trust.

The key considerations for compliant bat emergence surveys are:

  • Number of surveys required
  • Seasonal timing
  • Survey intervals
  • Survey methodology
  • Data validity periods

How Many Bat Emergence Surveys Are Required?

The number of surveys required depends on the bat roost suitability of the structure, as identified during the Preliminary Bat Roost Assessment, whereby:

  • Low suitability = One bat emergence survey
  • Moderate suitability = Two bat emergence surveys
  • High suitability = Three bat emergence surveys

Suitability is determined based on features such as:

  • Roof voids
  • Gaps and crevices
  • Construction type
  • Surrounding habitat

Seasonal Timing Requirements

Bat emergence surveys are seasonally constrained because bats are only active during certain times of year. The survey timing requirements are as follows:

  • Low suitability = Survey between May and August
  • Moderate suitability = Surveys between May and September, with at least one survey completed between May and August
  • High suitability = Surveys between May and September, with at least two surveys completed between May and August

To be compliant, all surveys should generally be completed at intervals which are at least three weeks apart.

The above means survey requirements can significantly influence project timelines, particularly where the need for surveys is identified late in the planning process.

What Happens During a Bat Emergence Survey?

During an emergence survey, ecologists position themselves around the structure to view all elevations from approximately 15 minutes before sunset and remain on site for up to two hours after sunset.

Surveyors monitor all elevations of the structure to identify bats emerging from, or entering, potential roost access points.

Because much of the survey takes place in darkness, specialist equipment is typically used, including:

  • Infrared cameras
  • Thermal imaging equipment
  • Bat detectors for recording bat echolocation calls

What Happens Next If No Bats Are Recorded?

Where surveys are completed in accordance with Bat Conservation Trust guidance and no bats are recorded emerging from or entering the structure, the likely absence of bats can generally be assumed.

In these cases:

  • No further bat surveys are usually required
  • A bat survey report is submitted with the planning application stating the likely absence of roosting bats can be assumed
  • Precautionary working methods may still be recommended during construction, such as briefing contractors on what to do in the unlikely event that bats are found during works

Planning authorities will typically rely on this information when determining the application.

What Happens Next If Bats Are Present?

If bats are recorded using the structure, a total of up to three bat emergence surveys (including those already completed) may be required to fully characterise the roost. If bat roost presence is confirmed, the bat emergence surveys are then termed ‘roost characterisation surveys’. The emergence surveys in this instance aim to identify:

  • Bat species present
  • Numbers of bats
  • Access & roosting locations
  • Roost type and significance
  • Seasonal use of the roost

This information is then used to prepare a Bat Mitigation Strategy. The mitigation strategy sets out:

  • How bats will be protected during works, including if the roost will need to be removed
  • Proposed mitigation and compensation measures, such as installation of bat boxes post-development
  • Whether a Natural England bat mitigation licence will be required

In almost all cases, planning permission can still be secured where bats are present, provided suitable Bat Mitigation Strategy can be demonstrated and submitted as part of the planning application.

Can Bat Boxes Be Provided Instead of Surveys?

In most cases, no.

Local Planning Authorities generally require protected species surveys to be completed before a planning application is determined, rather than relying on precautionary mitigation alone. This approach is informed by:

  • Government Circular 06/2005: Biodiversity and Geological Conservation
  • The Woolley v Cheshire East BC (2009) bat case

Together, these establish that planning authorities should have sufficient ecological information available before determining an application. As a result, “worst-case scenario” mitigation without survey evidence is rarely accepted, except in exceptional circumstances at the discretion of the planning authority.

How Long Are Bat Surveys Valid for Determining Planning Applications?

Survey validity is typically assessed by planning authorities with reference to the CIEEM guidance note: Advice Note on the Lifespan of Ecological Reports and Surveys. As a general guide:

  • Surveys up to 12 months of age are usually valid
  • 12 – 18 months are often valid, depending on site conditions and bat presence/ likely absence status
  • 18 months – 3 years are likely to require updated Preliminary Bat Roost Assessment, or updated bat emergence surveys
  • Survey data more than 3 years of age are unlikely to be accepted

Key Takeaway

Bat emergence surveys are often a critical planning requirement where buildings or structures have potential to support roosting bats and will be affected by the development proposals.

Because surveys are seasonally constrained and can influence planning determination timescales, early ecological assessment is essential to avoid delays to development programmes.

Undertaking a Preliminary Bat Roost Assessment at an early stage can help identify survey requirements and reduce planning risk later in the project.

Need Advice on Bat Survey Requirements?

If you are planning works to a building, bridge, or structure and are unsure whether bat surveys may be required, our team can help.

We support planning applications and construction projects via:

  • Preliminary Bat Roost Assessments (PBRAs)
  • Bat Emergence and Re-Entry Surveys
  • Roost Characterisation Surveys
  • Bat Mitigation Strategies
  • Planning support and ecological advice

We work closely with developers, architects, planning consultants, and councils to identify ecological constraints early and help projects progress efficiently.

To discuss a project or obtain a quote, contact our team.