Bat Surveys
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 internal and external inspection to identify potential roosting features such as cracks, holes, roof voids, and signs of bats such as droppings, urine staining or feeding remains
- Timing: Year-round, day time inspection
- Number of surveys: One (may require additional surveys on complicated or large sites)
Ground level tree assessments (GLTA)
- Purpose: Assess whether trees possess potential roost features (PRFs) for bats
- Method: Each tree is thoroughly examined from ground level using binoculars and a high power torch, where required to identify PRFs
- Timing: Year-round (ideally undertaken when tree canopies are not in leaf), day time inspection
- Number of surveys: One (additional visits may be required depending on number of trees)
Activity (Transect) Surveys
- Purpose: Record bat activity levels across a site to assess commuting routes, foraging areas and the value of a site for local bat populations, especially where significant habitat changes are planned
- Method: Surveyors walk a fixed route (transect) with bat detectors to detect flying bats
- Timing: From dusk to two-three hours after dark, April to October
- Number of surveys: One transect undertaken per season (Spring, Summer and Autumn)
- Automatic static detector surveys are often used in conjunction with these surveys (survey effort dependent on the suitability of commuting and foraging habitat and impacts of proposals)
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 required 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 set out to log bat calls
- Timing: Recording for a minimum 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 (November to March, targeting cold periods, typically during 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 using environmental DNA (eDNA) of droppings
- Use case: Support traditional methods or confirm species from droppings
- Limitation: Not a stand-alone method for legal purposes (yet)
Protected Species Licensing
Due to the strict legal protection afforded to roosting bats, a European Protected Species Mitigation (EPSM) 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.
An EPSM licence needs to be obtained from the statutory government body, Natural England.
An EPSM licence application can only be made once planning permission has been granted with all relevant conditions formally discharged.
Our team can help you secure a bat migration licence and ensure all necessary mitigation is done.