Bat Surveys

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Bats

There are 18 species of bat in the UK, all of which are protected under the Wildlife and Countryside Act 1981 and the Conservation of Habitats and Species Regulations 2017, which make it an offense to:

  • Deliberately capture, injure or kill bats
  • Damage or destroy a breeding or resting place
  • Obstruct access to their resting or sheltering places
  • Possess, sell, control or transport live or dead bats, or parts of them
  • Intentionally or recklessly disturb a bat while it's in a structure or place of shelter or protection

Where a development may affect bats or their habitat, bat surveys are required to assess their presence, activity, and potential roosts.

Bats can be affected by works including:

  • Demolition/maintenance of structures
  • Renovations to structures, bridges or tunnels
  • Conversion of churches, buildings or derelict properties
  • Tree/Hedgerow removal
  • Developments causing noise and light pollution
  • Developments removing green space, trees, hedgerows or ponds

If your Preliminary Ecological Appraisal or Preliminary Roost Assessment has identified the potential presence of roosting bats within your site - you may need one or more of the bat surveys listed down below:

Adonis Blue will work with you to carry out the necessary surveys to determine the presence of bats and attain a bat mitigation license on your site if necessary.

The best time of year to conduct a bat survey can be found within our ecology calendar.

Bat Surveys

Here are the main types of bat surveys used in development contexts:

Preliminary Roost Assessment (PRA)

  • Purpose: To assess the suitability of buildings or structures for roosting bats
  • Method: Visual external and internal inspection of features like cracks, holes, roof voids, or droppings
  • Timing: Year-round, day time inspection
  • Number of surveys: One (may require more on complicated or large sites)

Ground level tree assessments (GLTA)

  • Purpose: Assess whether tree poses potential roost features for bats
  • Method: Each tree is thoroughly examined from the ground level, using binoculars and a high power torch where required
  • Timing: Year-round, day time inspection
  • Number of surveys: One (may require more time on complicated or large sites)

Activity (Transect) Surveys

  • Purpose: Record bat activity levels across a site to assess commuting routes and foraging areas, especially where habitat changes are planned
  • Method: Surveyors walk a fixed route (transect) with bat detectors to detect flying bats
  • Timing: From Dusk to two hours after dark, May to September
  • Number of surveys: Can range from monthly to seasonal surveys, depending on the commuting and foraging suitability identified from the PRA / PEA
  • Automatic static detector surveys are often used in conjunction with these surveys

Aerial assessment (tree-climbing / MEWP) surveys

  • Purpose: Detailed inspection of potential roost features in trees previously identified and assessment of their suitability (none, PRF-I, PRF-M)
  • Method: Licensed ecologist to inspect cavities, cracks, or loose bark with endoscope where required
  • Timing: Year-round, day time inspection, optimal from May to August
  • Number of surveys: One inspection to determine suitability (more may be require to determine present or likely absence of roosting bats)

Emergence (Roost) Surveys

  • Purpose: Determine presence or likely absence of roosting bats and ascertain roost exit point
  • Method: Surveyors observe structures at dusk using bat detectors and night-vision aids
  • Timing: May to September but with at least half of the surveys being undertaken between May-August
  • Number of surveys: For buildings, number of surveys dependent on suitability can range from 1 to 3 surveys (1 survey = low, 2 surveys = moderate, 3 surveys = high)

Automated Static Detector Surveys

  • Purpose: Record bat activity continuously over several nights, around the bat activity season,to gain an understanding of the use and important for local bat populations (gathering information on species present, activity levels at different parts of the site and key habitat areas)
  • Method: Static bat detectors are left in place to log bat calls (for often 5 nights)
  • Timing: Put out for 5 consecutive nights, monthly from April-October
  • Number of surveys: Monthly (7 deployment in total)

Hibernation Surveys

  • Purpose: Identify and assess hibernation roosts (e.g., caves, basements)
  • Method: Careful internal inspections, sometimes using endoscopes, thermal imaging or statics
  • Timing: Winter months (typically December to February)
  • Number of surveys: at least 2 visits, with a third visit recommended for high-risk sites
  • Automated static detector surveys are often used in conjunction with these surveys

DNA and Environmental Sampling

  • Purpose: Detect bat presence from droppings, swabs, or environmental DNA (eDNA)
  • Use case: Support traditional methods or confirm species from droppings
  • Limitation: Not a stand-alone method for legal purposes (yet)

Obtain a protected species license

To obtain a bat licence for development, you need to apply for a bat mitigation licence from the relevant statutory nature conservation body.

This licence is legally required if your development will disturb bats or damage/destroy a known or suspected roost, even if bats are not currently present at the time of the works.

Our team can help you secure a bat migration licence and ensure all necessary mitigation is done.