Timing your bat survey is vital

If you’re planning a development scheme, it’s important to get the timings of bat surveys right to prevent a hold-up of many months.

This is because second-stage bat surveys (Bat Emergence Surveys) can only take place between May and September, the optimal time outside the bat hibernation period. If you miss this window, you could face a delay that takes your scheme well into the following year, potentially derailing your timetable.

So, to avoid planning delays, use a professional ecologist who holds a bat licence and will carry out the right bat survey at the right time of year.

Nathusius pipistrelle bats.

Why do you need a bat survey?

Bat numbers have declined dramatically due to development and the loss of green spaces which provide their natural habitat. As a result, bats are a protected species, legally protected along with other European protected species under the Wildlife and Countryside Act 1981 (as amended), and the Conservation of Habitats and Species Regulations (2017), which make it an offence to deliberately kill or disturb bats or obstruct access to their resting places.

According to the Bat Conservation Trust, there are 18 species of bat in the UK, ranging from the common pipistrelle to the rarer Bechstein’s bat.

Let’s look at the two types of bat survey that may be required: the first stage is the Preliminary Roost Assessment, which may need to be followed by a Bat Emergence Survey; here, the timing of your bat survey is crucial.

Stage 1 bat survey – the Preliminary Roost Assessment (PRA)

The best strategy is to get the PRA, or the bat scoping survey, carried out to find evidence of bats and assess your site’s potential for hosting bats. This bat survey can be undertaken at any time of the year. It involves an internal and external inspection of buildings, and the ecologist will look for:

  • The presence of bats.
  • Evidence of bat activity, for instance, droppings, urine stains, dead bat carcasses, and remains of prey.
  • Access to suitable roosting features (graded from low to high) which may include gaps in roofs or walls, loose hanging tiles, cracks in trees, flashing which is in poor repair, or proximity to woodland foraging areas.

A Preliminary Roost Assessment survey with an experienced consultancy like Arbtech costs from £399 +VAT. If the presence of bats is detected during the PRA, you will need a Bat Emergence Survey, a second-stage survey, which is carried out over several visits in the summer. Bat Emergence Surveys typically cost over £799+VAT.

A long-eared bat.

Stage 2 bat survey – the Bat Emergence Survey (BERS)

Your bat survey timing is vital here as a licenced ecologist will carry out an external and internal inspection of your site and relevant buildings at various times during the bat season, between May and September, the optimal period. Bat Conservation Trust guidelines state that surveys must take place around sunrise and sunset – 15 minutes before or two hours after sunset, or two hours before or 15 minutes after sunrise.

The ecologist will carry out exit and re-entry surveys on buildings that bats may take advantage of, and use technology such as bat detectors, infrared, night vision, and thermal imaging cameras to assess the number of bats on the site, looking at flight paths and tree roosts.

They also use voice recorders that convert bat echolocation calls into a frequency readout which enables species identification. As well as identifying the species of bat, it’s important to identify the type of bat roost which may be a day roost, night roost, hibernation roost, maternity roost, or transitional roost. Bat survey guidelines suggest that three surveys of this type may be needed to collect sufficient data over the summer time period.

Bats use different roosts at various times of the year to suit them as their requirements change in terms of humidity, temperature, noise, light, and wind. Once the roost type and species are established, the ecologist can propose appropriate mitigation measures.

Lesser mouse-eared bats and lesser horseshoe bats at roost.

Over several of these dusk and dawn activity surveys, ecologists will collect sufficient data for their BERS report, which will contain the survey findings and recommendations which can be submitted to the local planning authority alongside a planning application, which will hopefully enable your proposed development to proceed. 

If planning permission is granted by the local authority on the evidence of the report, you can make the required bat survey licence applications which will allow you to make alterations based on the mitigation proposals, and go ahead with your scheme.

Bat survey timing is vital

Getting your bat survey paperwork complete in good time will be crucial to keeping your scheme on schedule and enabling you to coordinate timings with all the other people you need to involve, such as builders and architects. Bat surveys are subject to the prevailing weather conditions and might be cancelled if there’s heavy rain or high winds, which is another reason for booking surveys in good time to allow for weather delays.

Contact an established ecological company that will be able to advise you further and help you comply with the legislation protecting bats.

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