What is in a bat report?

Bat Report

Why do I need a bat report?

You’ve submitted a planning application and the local authority have asked you to supply a bat report.  Here’s why.

All species of bat in Britain are legally protected – individual bats are protected from harm and disturbance and their roosts are protected from damage or destruction.  Local authorities also have a legal duty to pay ‘due regard’ to bats when performing their duties – which includes giving planning permission.  In addition, some species of bat are ‘Biodiversity Action Plan’ (BAP) species (well, BAP species have been superseded by Section 41 species, but BAP still sounds better!), which means that they are a material consideration in planning.

The LPA will therefore request a bat report to support any planning application that could effect bats and their roosts.  This will include most projects that involve modifying, converting or demolishing a building or mature trees.

The report will set out whether the site is suitable for bats, whether any additional surveys are needed and what should be done if bats are confirmed.

I’m only really discussing reports for an initial survey here, as that is what we cover at The Bat Surveyor – Preliminary Roost Assessments (or sometimes called Bat Scoping Surveys, and Initial Bat Report or simply a Bat Report.)

What should be in the bat report?

The bat report should be written in accordance with best practice.  This includes:

The report should include the bat surveyor’s name and credentials, the methods used for the survey and the results. The report should include clearly what category the potential suitability of the site for bats has been assessed as – negligible, low, moderate or high and any next steps needed to complete your project.

What does the ‘potential suitability’ of the site mean?

The Preliminary Roost Assessment aims to determine how suitable the structure is for bats to roost in, rather than necessarily proving that bats do, or do not roost there. Often we can demonstrate that bats do roost at a site (e.g. by seeing the bats or their droppings), but it is harder to demonstrate that bats don’t roost at a site based on a day-time visit. The suitability is given as negligible, low, moderate or high.

You could think of the suitability as the ‘risk’ of bats occurring, but that isn’t quite right as the assessment isn’t supposed to consider the local environment, just the structure itself.  You could therefore have an old building with lots of nooks and crevices that bats like to squeeze into in the middle of a concrete car-park and technically it will be assessed as ‘high’.  In our reports if there is a disparity between the suitability of a structure and the chance of their actually being bats in it, we make this clear and modify our recommendations rather than slavishly following the guidance.

The full definitions are given in the table below, but the following is a summary.  I use ‘structure‘ to mean whatever is being surveyed such as a tree, house or bridge. ‘Feature‘ means a specific part of the structure that a bat could use to roost, like a loose roof tile, or a rot hole in a tree.

Negligible – No features that bats could roost in. There is no need to consider bats further.

Low – There are some features on the structure that bats could roost in, but if they do they are only likely to do so opportunistically, like if they are caught out in bad weather.

Moderate – There features on the structure that could be used by a small number of bats occasionally.

High – There are a number of features in the structure, or the features could support an ‘important’ roost. An important roost could be a maternity colony (where pregnant females gather, give birth and nurse their young) or a hibernation site (where bats go into torpor over winter).

  • Negligible



    Negligible habitat features on site likely to be used roosting bats.

  • Low



    A structure with one or more potential roost sites that could be used by individual bats opportunistically.

    However, these potential roost sites do not provide enough space, shelter, protection, appropriate conditions and/or suitable surrounding habitat to be used on a regular basis or by larger numbers of bats (i.e. unlikely be suitable for maternity or hibernation).

    A tree of sufficient size and age to contain PRFs but none seen from the ground or features seen with only very limited roosting potential.

  • Moderate



    A structure or tree with one or more potential roost sites that could be used by bats due to their size, shelter, protection, conditions and surrounding habitat, but unlikely to support a roost of high conservation status.

  • High



    A structure or tree with one or more potential roost sites that are obviously suitable for use by larger numbers of bats on a more regular basis and potentially for longer periods of time due to their size, shelter, protection, conditions and surrounding habitat.

    A structure or tree with one or more potential roost sites that are obviously suitable for use by larger numbers of bats on a more regular basis and potentially for longer periods of time due to their size, shelter, protection, conditions’ and surrounding habitat.

What might the bat report recommend?

A good surveyor will assess the structure and its features, then try to eliminate as many of the features as they can by demonstrating that bats don’t use them (e.g. by checking them with an endoscope).  Any features that can’t be ruled out are used to determine the potential suitability of the structure for roosting bats. As I said above, this should also be put in context with the site and its surroundings to consider how likely a bat roost is. This means that recommendations for additional surveys should only be made after a thorough daytime survey and consideration of the site.  I’m not saying that additional work is never needed, but that a considered approach should be taken.

You should expect the report to be written in accessible English, not just jargon, and for the conclusions to be justified.  If an ecologist is telling you you need to spend more money with them doing more surveys, the bat report really should give you a clear understanding why.

Bat Surveys

If the structures were assessed as low, moderate or high, The report could recommend additional surveys to demonstrate whether bats actually roost at the site or not.  These are usually dusk surveys or pre-dawn surveys.  As it sounds, this involves ecologists coming to the site at night.  They will have bat detectors (which transpose and record bat echolocation calls) and may have night-vision equipment.

Typically for a low potential structure, this would be one dusk or one pre-dawn survey.  The survey can be completed at any time between May and September inclusive.

For a moderate potential structure, this would be two surveys between May and September, but one of which should be a pre-dawn survey and one of which should be between May and August inclusive.

For a high potential structure, three surveys are likely to be recommended. Again one needs to be a pre-dawn survey and one needs to be bewteen May and August.

Bat Mitigation, Compensation and Enhancement

The bat report should also consider what the impacts to bats would be if they are there and set out appropriate mitigation, compensation and enhancement

Mitigation – what can be done to deliver the project, but reduce impacts to bats.  This might include slight redesigns, but also methods of working to avoid harming bats.

Compensation – if all the impacts can’t be avoided, what can be done to compensate for impacts.  This might be creating new roosts to replace those that are lose.

Enhancement – what can be done to make the site better for bats after the project than it was before.  Perhaps additional roosts would be useful, or better planting and lighting around the site.

What else should your bat report include?

You should expect the report to include detailed results of the survey, photos that illustrate the results or assessment and plans.  A summary of the legislation that is relevant to the project should be included as well.  We’d keep all this additional information in appendices so that the main report isn’t cluttered or too thick to wade through.