Bat survey season is the single most common cause of a planning application losing a year. It is also largely avoidable, provided you know which parts of the work are season-limited and which are not.
Preliminary roost assessments: all year round. The daytime inspection that establishes whether a building has bat roost potential can be carried out in any month, including December.
Dusk emergence surveys: broadly May to August. These are the dusk watches that establish whether bats are actually using a structure. April and September can sometimes be used with caveats depending on conditions, but the reliable core of the season is May to August.
Winter: little that is useful. Bats are largely inactive, and an emergence survey carried out in winter tells a case officer very little.
Emergence surveys work by watching bats leave a roost at dusk. That only produces meaningful evidence when bats are active and using summer roosts. Outside that window, an absence of bats emerging proves nothing at all — which is why councils and consultees will not accept out-of-season survey results as evidence of absence.
A typical sequence goes like this. An application goes in during October. The council asks for a biodiversity checklist in November. The checklist flags roost potential on an old byre in December. Emergence surveys are then commissioned — and cannot be carried out until May at the earliest, with the report following in June or July.
That is eight months lost, none of it anyone's fault, and all of it avoidable by doing the roost assessment first.
Bats are not the only thing with a calendar. Habitat surveys underpinning a preliminary ecological appraisal are most reliable between April and September, when vegetation is identifiable. The bird nesting season, conventionally taken as March to August inclusive, restricts vegetation and hedgerow clearance. Badger and other protected species work has its own timing considerations.
None of these need hold a scheme up on their own. They are reasons to find out early which of them apply to yours.
Preliminary roost assessments can. Dusk emergence surveys cannot produce usable results in winter, because bats are not active and an absence of emerging bats does not demonstrate absence of a roost.
April can sometimes be used, subject to weather conditions and the species likely to be present, but it carries caveats. May to August is the window that a council or consultee will accept without question.
The usual route is to agree a survey timetable with the case officer, so the application is not refused for lack of information while the surveys wait for spring. Getting the preliminary roost assessment done in the meantime strengthens that conversation considerably.
Written by John Corry of Corry Ecology, CIEEM member. General guidance only — every site is different, so take advice on your own proposal.
Send the site address and a short description and I'll come back with a quote and a likely timescale.
