Programming a scheme around bat survey seasons
A preliminary roost assessment can be done in any month, but emergence and re-entry surveys are limited to the maternity season. Survey effort by roost potential, and how to keep the rest of the scheme moving.
Bat survey season decides your planning programme more often than the planners do. A preliminary roost assessment can be carried out at any time of year. Emergence and re-entry surveys, the ones that tell you whether bats actually use the building, can only be done between May and September, with May to August the part of that window ecologists treat as reliable. Miss it and the next opportunity is the following May.
That is the whole problem in two sentences. Everything else is about how you arrange the rest of the scheme around it.
What a preliminary roost assessment can be done when
The first visit is a building and habitat inspection by a licensed ecologist, looking for access points, droppings, staining, feeding remains and features with roost potential, together with a desk study of local records. It happens in daylight, in any month, and it produces one of three outcomes: negligible potential, so no further survey; roost potential with no evidence found, so emergence surveys are needed; or confirmed roost, in which case you are heading for a licence.
Book it first and book it early. A preliminary assessment in January costs a fraction of what a delayed scheme costs in June, and it is the only ecology work that is never season limited. We set out what the categories mean in what a preliminary roost assessment can conclude.
One thing it cannot do is clear a building with obvious roost features on its own. An assessment that finds moderate or high potential is a gateway to further survey, not a substitute for it.
The emergence and re-entry survey window
Emergence surveys are dusk watches, with observers positioned to see every elevation as bats leave. Re-entry surveys are the dawn equivalent. Both depend on bats being active and breeding, which is why the window follows the maternity season rather than the calendar year.
The Bat Conservation Trust Good Practice Guidelines, now in their fourth edition, set the survey effort by the roost potential found at the preliminary stage.
| Roost potential | Survey visits | Window |
|---|---|---|
| Negligible | None | Not applicable |
| Low | One | May to August |
| Moderate | Two | May to September, at least one in May to August |
| High | Three | May to September, at least two in May to August |
Visits must be separated by at least two weeks, which means a high potential building needs around six weeks of survey from the first visit to the last. Weather matters too. Surveys are not valid in heavy rain, strong wind or low temperatures, so an ecologist will abort and rebook, and a cold wet June can push a three visit programme into August.
Work the arithmetic backwards from your target submission date. A high potential building surveyed from late May finishes in mid July, with the report a fortnight later. Start in mid August and you will not finish at all.
How many visits a building needs
The table above is the starting point, not the answer. Three factors push effort upwards.
Multiple structures. A farmstead with a house, a barn and two outbuildings is not one survey. Each structure with roost potential carries its own effort, although visits can often be combined with enough surveyors.
Species sensitivity. Where a horseshoe bat or an annex II species is suspected, or where a maternity roost is confirmed, expect additional survey including internal inspection, static detectors and sometimes radio tracking to find the wider roost network.
Scheme impact. Demolition and roof stripping demand more certainty than a scheme that leaves the roof void untouched. An ecologist asked to support a demolition on one survey visit will say no, and they are right to.
Councils generally will not determine an application without the survey information, and asking for the survey to be dealt with by condition rarely works where a protected species is reasonably likely to be present. Natural England's standing advice is clear that sufficient information is needed before the decision, and the decision maker has a duty to consider the licensing tests. Our comparison of a preliminary roost assessment against an emergence survey explains the difference in what each delivers.
What happens if you miss the season
Four options, in descending order of attractiveness.
Wait. Unglamorous, predictable, and often the least costly answer once you count the cost of the alternatives.
Redesign to avoid the impact. Where the bat interest is in one roof void or one gable, a scheme that retains the feature untouched, with a buffer and no lighting change, can sometimes be supported on a precautionary basis. This needs the ecologist to be comfortable that no offence will occur, and they will want physical separation rather than good intentions.
Submit with the survey programmed and the application held in abeyance. Some authorities will accept validation, consult, and then wait for the survey report before determination, with an extension of time agreed. This keeps the clock running on everything else. Ask before you rely on it.
Apply for outline permission with ecology as a reserved matter. Rarely available where the protected species question goes to the principle of development, and it adds a reserved matters stage.
What does not work is submitting without the survey and offering a condition. On a building with moderate or high roost potential that invites a refusal, and the refusal is hard to overturn on appeal.
Interim steps that keep the programme moving
While you wait for May, there is a surprising amount to get on with.
- Commission the preliminary roost assessment and the desk study, including a records search from the local environmental records centre
- Carry out the habitat work that is not season limited: a BS 5837 tree survey, the topographical survey, drainage investigations and ground investigation
- Settle the design, because a design change after the bat survey can invalidate the mitigation
- Deal with the biodiversity net gain baseline, noting that habitat condition assessment has its own botanical season from April to September
- Check for other season limited constraints, particularly nesting birds from March to August, covered in nesting bird checks before vegetation clearance
- Get the pre-application advice and the validation checklist confirmed
Sequence the ecology properly and one summer does the work of two. A preliminary assessment in February, emergence surveys from May, a Protected Species Survey report in July and a licence application in the autumn is a tight but achievable programme for a barn conversion.
Costs of delay against costs of early survey
The comparison that matters is not survey fee against no survey fee. It is survey fee against the cost of holding a site for a further year, including finance, professional fees already spent, and in many cases the risk that a policy or standard moves against you.
Bat survey fees vary with the number of structures, the number of surveyors needed and travel. Ask for a fee based on the survey effort the preliminary assessment identifies rather than a single figure quoted before anyone has looked at the building. And ask what the fee includes: report, mitigation design, licence application and the ecological clerk of works role during works are often priced separately.
A licensed ecologist is legally required for this work. Surveys and any mitigation licence sit under the Wildlife and Countryside Act 1981 and the Conservation of Habitats and Species Regulations 2017, and a licence application to Natural England has to be made by a suitably licensed person. An AI-assisted draft is a starting point for that professional rather than a substitute for them.
Writing the programme into the application
Do not hide the sequencing. A short programme note in the covering material, cross referenced from the ecology report, tells the officer that you understand the constraint and reduces the chance of a holding objection.
Include the dates of each survey visit, the weather conditions, the surveyor names and licence numbers, and the species recorded. Where a licence will be needed, say so, state which Natural England licence route you expect to use, including any low impact class licence, and confirm that the three licensing tests are addressed in the mitigation strategy. Where works are to be supervised, propose the condition wording yourself.
A last point on honesty. If the survey finds a maternity roost, the scheme changes. Mitigation on that scale means a purpose built roost, a timed works programme avoiding the maternity period, and post development monitoring for several years. Better to know in July than to find out when the roof comes off.
Enter your postcode on PlanScope to see which ecology documents your site is likely to need, then send the draft for professional review.
This is general guidance rather than 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.
Frequently asked questions
Can a bat survey be done in winter?
A preliminary roost assessment can, because it is a daylight inspection for access points, droppings, staining and roost features together with a desk study. Emergence and re-entry surveys cannot, because they depend on bats being active. Winter hibernation surveys exist for specific structures such as ice houses and tunnels, and they answer a different question.
How many emergence surveys does my building need?
It depends on the roost potential recorded at the preliminary stage. Following the Bat Conservation Trust guidelines, low potential generally needs one visit, moderate potential two and high potential three, with visits at least two weeks apart. At least one visit for moderate potential and two for high potential should fall between May and August.
Will the council accept a condition requiring a bat survey after permission?
Rarely, where a protected species is reasonably likely to be present. Natural England standing advice is that sufficient ecological information is needed before the decision, because the authority has to consider whether the licensing tests could be met. On a building with moderate or high roost potential, submitting without survey information invites a refusal.
Who is allowed to carry out a bat survey?
A suitably licensed ecologist. Bats are protected under the Wildlife and Countryside Act 1981 and the Conservation of Habitats and Species Regulations 2017, and survey work involving disturbance or access to roosts requires a survey licence from Natural England. Any mitigation licence application must also be made by a suitably licensed person, so this is not work an applicant can do themselves.
What should I do if I have missed the survey window?
Usually wait, and use the time for the preliminary assessment, tree and topographical surveys, ground investigation and the biodiversity baseline. Alternatives are to redesign so the roost feature is untouched, or to agree with the authority that the application is validated and consulted on while the survey is programmed, with an extension of time.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.