Reporting a bat survey done outside the emergence season

A bat survey carried out in November can establish what roosting features a building has, what evidence of use is present, and how suitable those features are. It cannot establish absence. Emergence and re-entry surveys run from May to September, with the strongest results between May and August, and nothing done outside that window substitutes for them. So the honest winter report says what was found, states the roost suitability category, and sets out what further survey is needed and when.

Where a report blurs that line, the consequence falls on the client. A council that grants permission on inadequate survey evidence has not discharged its duty, and a licence application built on the same evidence is refused.

What can and cannot be concluded in winter

A preliminary roost assessment can be done at any time of year. The inspection looks for access points and crevices, and for field evidence: droppings, urine staining, feeding remains, scratch marks, staining around gaps in flashing and ridge tiles, and the smooth polished surfaces at regularly used access points.

From that a competent surveyor can reach three kinds of conclusion. That a confirmed roost is present, where droppings or live bats are found. That the building has features suitable for roosting, graded by the recognised categories of negligible, low, moderate or high suitability. Or that suitability is negligible, where the structure offers no access point or crevice at all.

What cannot be concluded is absence from a building with moderate or high suitability. Bats use different roosts through the year, a maternity roost occupied in June may show little in November beyond old droppings that are easy to miss, and crevice-dwelling species leave very little trace at all.

Negligible suitability is the one winter conclusion that can close the question, and it has to be evidenced with photographs of the relevant junctions rather than asserted.

Preliminary roost assessment against emergence survey

The two do different jobs and the report should never imply otherwise.

Survey effort for emergence work scales with suitability. Published good practice guidance sets out the expected number of visits for low, moderate and high suitability structures, with the visits spread across the season rather than clustered in one month. A report that proposes a single August visit on a high suitability barn is proposing a survey that will not support a licence.

Where a building has already been assessed in a previous year, data has a working life. Councils and Natural England expect survey information to be current, which in practice means refreshed where it is more than two or three years old, and sooner where the building has changed.

Recording features without activity data

The winter report earns its fee through the quality of its feature record, because that record is what the following summer's survey is designed around.

What to include:

• An annotated elevation drawing with every potential access point numbered, not a written list
• Photographs of each feature at a resolution that shows the gap, with a scale where the dimension matters
• Internal inspection of the roof void where access is safe, with the extent of the inspection stated and any area not reached identified
• A record of the evidence found at each feature, including the quantity and condition of droppings and whether they were collected for identification
• The suitability category for the structure as a whole and, where it varies, for each element
• Habitat context: connectivity to hedgerows, treelines and watercourses, and lighting levels around the building
• Trees on or adjacent to the site with their own roost feature potential, assessed separately

Stating what was not inspected matters as much as stating what was. A roof void reached only from a loft hatch at one end, with no crawl boards, is a partial inspection, and saying so protects the conclusion rather than weakening it.

Precautionary assumptions and their consequences

Where further survey cannot be done before the application has to be submitted, the alternative is a precautionary approach: assume the worst credible roost type consistent with the features found, and design mitigation for it.

That works where the risk really is low. A modern building with a single lifted tile and low suitability can reasonably be handled by a precautionary method statement, with a toolbox talk, soft stripping by hand under supervision, and a stop procedure if a bat is found.

It does not work where suitability is moderate or high. A precautionary assumption cannot tell you the species, the roost type or the numbers, and a European Protected Species licence application needs all three. Natural England assesses the derogation tests on the evidence submitted, and an application that cannot characterise the roost does not get through.

There is also a legal point that no amount of precaution answers. Surveys and any mitigation licence require a suitably licensed ecologist under the Wildlife and Countryside Act 1981 and the Conservation of Habitats and Species Regulations 2017. An AI-assisted draft can structure a Protected Species Survey report and its method statement; the survey itself, the species identification and the licence application are work only a licensed ecologist can lawfully do.

Conditions requiring survey before works

The familiar request is a condition requiring bat surveys before development begins. It is a reasonable condition in some cases and unlawful in others.

Planning practice guidance on the natural environment treats the presence of a protected species as a material consideration, which means the decision-maker needs enough information to understand the effect on the species before granting permission. The authority also has its own duty under the Habitats Regulations to have regard to the requirements of the Directive, and the courts have held that where a licence will be needed the authority must consider the derogation tests itself rather than leaving them entirely to Natural England.

So the distinction is about risk. Where suitability is negligible or low and the mitigation is straightforward, a condition securing a precautionary method statement is proportionate. Where a roost is likely, deferring the survey to a condition asks the authority to grant permission without knowing whether the development can lawfully proceed, and that is the situation refusals and judicial reviews come from.

Say which of the two situations applies, in the report, in one clear sentence. Officers are grateful for it.

How a council treats the gap

Expect one of four responses, and they are predictable from the suitability category.

Negligible suitability, evidenced: the ecology issue closes and the application proceeds. Low suitability: a condition requiring a precautionary method statement and often a bat box or two as enhancement. Moderate suitability: the officer will usually ask for the emergence surveys before determination, or hold the application until they are done. High suitability or a confirmed roost: surveys before determination, and a mitigation strategy and licence route set out in the submission.

A fifth response happens on larger schemes. The officer accepts the application as valid, consults the county ecologist, and the ecologist's response asks for the surveys. That consumes six to eight weeks before you learn anything, which is worse than the honest answer at the outset.

Where the site has a wider ecological interest, the seasonal constraints usually extend beyond bats, and the Preliminary Ecological Appraisal should list every survey window the scheme depends on in one table.

Programme implications for the applicant

The arithmetic is unforgiving. A winter assessment that recommends three emergence surveys on a high suitability building means the earliest full data set is late summer, a mitigation strategy a few weeks after that, and a licence application only once permission is granted, since Natural England will not issue a licence without it.

On a project that wanted to start on site in spring, that is a year.

Three things shorten it. Commission the preliminary assessment in autumn rather than in March, so the survey programme is booked before ecologists' summer diaries fill. Design the mitigation in parallel with the surveys rather than after them, using the suitability assessment to scope the likely requirement. And where the scheme can be phased, separate the elements that affect the building with roost features from those that do not.

The honest uncertainty is in survey results themselves. A building with high suitability can produce three blank surveys, and that outcome, properly reported, is a result rather than a failure. A Bat Survey report should state the weather conditions, equipment and surveyor positions for each visit so a reviewer can judge whether a negative result is reliable.

The professional directory is the route to a licensed reviewer, and for specialist technical reports, qualified professional input may be required. Enter your postcode on PlanScope to see which reports a site with roosting potential is likely to need.

This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.