Bat survey timing is the single most common cause of planning delay on small projects, and it is entirely predictable. The daytime assessment can be done at any time of year. The dusk and dawn surveys that follow can only be done while bats are active, and that window closes for the winter whatever the project timetable says.
Bat survey season UK: the active months
Emergence and re entry surveys are carried out in the warmer months when bats are out foraging, with the core of the season in the middle of it and shoulder months treated cautiously. Your ecologist will name the dates they will work to and the guidance they follow.
How long results stay current
Survey results age. Authorities commonly treat bat survey data as valid for around a year to eighteen months depending on the site and the scheme, after which they may ask for an update. Get the survey when the design is settled enough that it will still describe the scheme when the application goes in.
The nesting bird season runs in parallel
The bird nesting season overlaps the bat season and restricts vegetation clearance and roof works separately. Two constraints, two calendars, one programme, and both are worth marking before a contractor is booked.
Planning the programme backwards against an ecological survey calendar
Work back from the planning submission: report writing, the visits, the assessment, the appointment. A project that starts that sequence in late summer usually makes the season; one that starts in October usually does not.
The bat breeding season UK surveys have to work around
Females gather into maternity roosts from about May, give birth to a single pup in June or early July, and the young are flying by late August, which is why the summer is both the best time to survey and the worst time to do the work. Emergence and re entry surveys need bats to be active, so the recognised window for them runs from May to August, with the height of the maternity period being when a roost is most obvious and most sensitive. Between November and March bats are hibernating: a roost can be inspected for evidence, but nobody can count what is not flying, so a survey done then answers a narrower question and often has to be repeated in season. The practical consequence for a project is the calendar rather than the cost, and the mistake is to discover in June that a licence needs a summer's worth of surveys before anything can be disturbed.
Reptile surveys, and the season they have to run in
Reptiles are surveyed by a different method and in a different window from bats, and confusing the two costs a season. The four widespread species are protected against killing and injury, so a site with suitable habitat, rough grassland, scrub edges, south facing banks, brash piles or brownfield rubble, needs a presence or absence survey before it is cleared. The method is artificial refugia: mats or tins laid out, left to bed in, and then checked on a number of visits in suitable weather. The season is the active one, broadly April to September with the best results in spring and early autumn, avoiding the hottest part of high summer when animals are under cover, and nothing useful can be done in the winter while they are hibernating. The practical consequence is the same as for bats: the survey has to happen before the clearance, and discovering the requirement in November means waiting for spring or redesigning the works.
Questions people ask about bat survey season
When can bat surveys be carried out?
The preliminary daytime assessment at any time. Emergence and re entry surveys only during the active season, which your ecologist will define against current good practice guidance.
How long is a bat survey valid for?
Commonly around twelve to eighteen months, at the planning authority's discretion and depending on how much the site or the scheme has changed.
Can I apply for planning while waiting for surveys?
You can submit, and the authority may refuse to validate or determine without the ecology. Ask the case officer before relying on it.
When is bat season UK surveyors work to?
The seasons that matter are set by what bats are doing. A preliminary roost assessment can be done at any time of year, which is why it is the first thing to book. Emergence and re entry surveys, the ones that actually confirm a roost, run May to August with the best results in May to July, and a single late season survey is often not enough. Hibernation surveys are December to February and answer a different question. Because planning conditions usually require the emergence surveys, a scheme that reaches the ecologist in September has lost a year unless the roost assessment clears it.