© Daniel Hargreaves
Local planning authorities normally require a bat survey to be undertaken where a development has a reasonable likelihood of affecting bats or their roosts. Bats are also legally protected from harm and disturbance, and their roosts are protected from damage and destruction. This means that, where there is a reasonable likelihood of bats being affected by development, their presence or otherwise should be established so that appropriate measures can put in place, if necessary.
Bat roost surveys
The first stage in conducting a bat roost survey is normally a daytime visit to assess any potential roosting features (such as buildings, trees, bridges and tunnels) that could be affected by the development. The assessment includes searching for evidence of bats, recording potential roosting locations and the location of any potential access points for bats. The features are then graded (as negligible, low, medium or high) for their potential to support roosting bats.
For buildings, this type of survey is called an internal and external building inspection for bats (also called a preliminary assessment for bats or a stage 1 inspection). For trees, this type of survey is known as a ground-level tree assessment. These surveys can normally be combined with an extended phase 1 habitat survey to save time and money.
If no evidence of bats is recorded and there are no features with the potential to support roosting bats then no further survey will be required and a report will be produced to this effect. Where features were recorded that have the potential to support roosting bats, further survey is normally recommended to determine whether bat roosts are present or absent.
Further surveys normally comprise dusk emergence and dawn return to roost surveys (also known as stage 2 surveys, dusk / dawn surveys or emergence / return to roost surveys). This comprises an ecologist watching potential access points at dusk to record bats emerging from a feature and at dawn to record bats returning to roost. The Bat Conservation Trust set out guidelines for the minimum amount of survey required to determine the presence or likely absence of bats (BCT, 2012). There may be other options available at this stage, including tree climbing assessments, hibernation checks and DNA analysis of droppings.
Where no roosting bats have been recorded, then it can normally be concluded that there is a likely absence of bats and no further action is required. Where roosting bats have been recorded, suitable measures may need to be put in place to enable the local planning authority to grant planning consent and for the development to proceed lawfully. See our bat mitigation page for more information.
Bat activity surveys
For larger schemes, local planning authorities may require an assessment to be undertaken to determine the presence of any important features on the site for bats. This may include identifying any important linear features used by bats (such as hedgerows) or important areas of foraging habitat. Two types of survey can be undertaken to achieve this: bat activity transects and static monitoring for bats.
Bat activity transects comprise an ecologist walking pre-determined routes around a site whilst simultaneously recording bat activity. Static monitoring for bats comprises deploying static monitoring detectors (such as AnaBat Express or SM2 detectors) that record bat activity at a particular location. The Bat Conservation Trust set out guidelines for the minimum level of survey effort based upon the size of the site and the type of habitats present (BCT, 2012). However, it may be appropriate to modify the amount of survey required based on the likely impacts of the development.