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What you need to know about bat surveys

A Common Pipistrelle bat.

Why are bats protected?

Populations across all 18 UK bat species have been in decline over the last 50-100 years due to increased development resulting in the loss of their natural habitat. In response to this, protection for bats has been increased via Schedule 2 of the Conservation of Habitats and Species Regulations 2017 and Section 9 of the Wildlife and Countryside Act 1981. Bats are fully protected and harming bats is a criminal offence; anyone seeking planning permission to develop buildings or sites involving trees or other potential roosting sites, has a legal obligation to avoid disturbing bats. It is illegal to:

  • Deliberately kill or injure bats.
  • Deliberately capture a bat.
  • Deliberately disturb bats whether they are at roost or not.
  • Damage, destroy or obstruct access to bat roosts.
  • Possess or transport a bat, or any part of a bat, unless it has been legally acquired.
  • Sell, barter or exchange bats or any part of a bat.

If you find bats, it doesn’t mean the end of your development proposals. You may be able to proceed in certain circumstances if you can provide appropriate mitigation and compensation measures for the relevant species of bat and the net loss of habitat. If you need a bat survey, be aware that local planning authorities differ in their requirements, so it’s important to find out what your local authority will ask for; consulting a professional ecologist will help you progress from here.

What is a bat survey?

Bat surveys find out whether bats are present on a specific site or may use it at certain times of the year. There are several types of bat survey: a Preliminary Roost Assessment (stage 1) which is carried out before the more detailed Bat Emergence and Re-entry Survey (also known as an Activity Survey or Phase 2 Survey).

There are also Hibernation Roost Surveys. Bat surveys that may result in disturbance to a roost should be carried out by a licensed bat consultant; licences are issued by the statutory nature conservation bodies Natural England, Natural Resources Wales and NatureScot. The length of time that a bat survey is valid depends on the local planning authority, but all are valid for 12 months and they usually extend for up to 24 months. Natural England regards bat surveys as having a shelf life of under two seasons old.

What is a bat roost?

It is a feeding or resting place that can be in caves, tree cracks, lofts, barns, under weather boarding, on gable ends, ridge tiles or under loose or hanging tiles, which suit crevice dwelling bats. A perfect roost site offers bats a safe place in which to hibernate and raise their young while having access to a food source – usually insects and water. Bats will relocate to different roosts over the course of a year as their requirements change, so several roosts may be occupied over a season. Types of roost include a maternity roost, day roosts, transitional roosts, feeding roosts, and hibernation roosts; each has different benefits, but they must all provide safety from predators, the correct temperature, humidity, and offer protection from noise, wind and light.

A Natterers bat.

If you need to obtain a bat survey, these are the steps to take:

  1. A Preliminary Roost Assessment.
  2. If required, a Bat Emergence and Re-entry Survey and/or a Hibernation Roost Survey.
  3. Propose appropriate mitigation and compensation measures for bats in your planning application.
  4. Submit an application and obtain planning permission.
  5. If required, apply for a European Protected Species Licence.

A Preliminary Roost Assessments (PRA) or Scoping Bat Surveys (stage 1)

These are internal and external inspections of buildings that can be carried out at any time of year. The aim is to exclude the following three factors which trigger further surveys:

  1. The presence of bats.
  2. Evidence of bat activity, such as feeding remains, bat droppings, urine stains, fragments of prey or dead bat carcasses.
  3. Access to features suitable for roosting bats, graded from low to high.

If this bat survey reveals the presence of bats, or that there are roost features that they could use, such as loose tiles in slate roofs, gaps in brickwork or proximity to woodland – then you must propose mitigation or habitat gains for bats as part of your development proposals; your scheme would result in a net loss of habitat without such mitigation.

Bat Emergence and Re-entry Surveys (BERS)

Carried out following a PRA survey which has found evidence of bats, or features that could support roosting bats, this bat activity survey is the second phase of the initial assessment process. A bat surveyor will visit the site and monitor potential bat exit points and access points to gather data, using specialist equipment such as bat detectors, infrared lights, night vision, and thermal imaging cameras along with detectors that convert echolocation calls into an audible readout. The calls of different species of bat differ, so this can help with identification.

The findings and recommendations, along with details of the effect that the development proposals would have on the bats, form the basis of this further survey. It will also contain mitigation measures to enable the planning application to progress, along with details including the type of roost, species and bat numbers. The number of bat surveyors and site visits required by a BERS depends on the PRA results; bat activity surveys typically involve 2 or 3 surveys at dusk and dawn.

Bat survey season

Bats hibernate in winter as there are fewer insects for them to feed on, so BERS (also known as dusk and dawn surveys) are carried out in the summer months, typically between May and September, as the sun rises or sets, when bats emerge from or return to a roost. They are undertaken 15 minutes before or two hours after sunset, or two hours before or 15 minutes after sunrise. Some local planning authorities will accept surveys done in the sub-optimal weeks in April and between September and October providing that weather conditions are suitable. High winds or heavy rain may cause bat activity surveys to be cancelled, so it’s a good plan to factor this in and book early.

Your planning application, supported by a Scoping Survey and/or Bat Emergence Survey report will enable you to secure planning permission. While it may be necessary in some circumstances to obtain a European Protected Species Licence for your application, it will not stop you from obtaining planning consent from your local planning authority.

Hibernation Roost Surveys

Also carried out following a PRA survey, Hibernation Roost Surveys may be required where a building has suitable features or conditions for winter hibernation. A Hibernation Roost Survey will entail two visits between December and February to inspect the building for hibernating bats. Static detectors may also be deployed for longer periods to record any bat activity and the thermal conditions of the building. Buildings which might shelter hibernating bats include old and listed buildings, livestock buildings, barn conversions in rural communities, and agricultural buildings.

European Protected Species Licence (EPSL) applications

If investigations reveal the presence of a bat roost and it needs to be disturbed, damaged, or destroyed as part of your development, an EPSL will be required from Natural England. This can take an average of six weeks. Where roosts of low conservation value are found i.e., small numbers of common bat species, a new type of license is available in England – a Low Impact Class Licence or a Bat Mitigation Class Licence. This is held by a registered consultant and obtaining this can be faster than a full EPSL.

A Noctule bat.

Bat mitigation work

The bat surveys collate data to establish:

  • The species of bat present.
  • The bat population.
  • How bats use the site.

Having gathered the survey data, a professional ecologist can recommend appropriate mitigation measures in the bat survey report, with the aim of preventing habitat loss and maintaining existing habitats. Examples of simple mitigation measures might involve installing bat boxes on site to provide alternative roosts, or fitting bat access roof tiles. Bat boxes can be fitted to trees and buildings. Large bat species have more demanding requirements, for example, brown long-eared bats need a void in which they can practice making short flights, such as a sectioned-off roof void or loft. There may also be timing implications, depending upon the bat roosts present, and a specific working method is likely to be required.

Where bat surveys are less likely to be needed

Bats are less likely to be found in new-build houses which are well-sealed and insulated, urban areas surrounded by little green space, industrial buildings, prefabricated buildings built from sheet steel, small, cluttered roof spaces or dilapidated property which does not offer a stable environment in terms of temperature and light. However, bats are very resourceful, and therefore a bat survey may still be required.

Four Pipistrelles in a church tower

How to get a bat survey

If there’s a reasonable likelihood that your scheme will affect bats and a bat survey is required, you need to contact a suitably qualified ecological consultancy like Arbtech. Professional ecologists holding a bat licence will be able to give you detailed guidance if you need a bat survey, advising on the type of bat survey you need, and the bat survey season timeframes.

They will also be able to offer further advice about bat survey cost options. Getting in touch with an ecological consultancy early on is recommended to maximise the chances of your planning application being approved the first time by your local planning authority avoiding delays to your development proposals.

Bat facts

  • Bats are the only flying mammal.
  • They have four long fingers and a thumb, connected by a thin layer of skin to form wings.
  • All bat species in the UK exclusively eat insects. These may be caught in flight and eaten on the wing or brought back to the roost to eat – while hanging upside down.
  • 75% of UK bat sightings are of the common Pipistrelle: this is also the smallest UK bat, having a wingspan of 22cm. They have a brown back with lighter colouring on their stomachs and dark faces.
  • The largest UK bat is the Noctule bat which has a 36cm wingspan. It has light brown fur and dark ears, wings and face.
  • Bats will nestle in crevices or hang upside down to roost; as they cannot launch from an upright position, this enables them to release their grip and drop into a glide.
  • Bats hibernate upside down between November and March, maintaining a constant body temperature and living off stored fat.
  • Females gather in a maternity roost to give birth, usually to one pup a year.
  • The lifespan of a bat varies from five years to several decades depending on the species: common Pipistrelles can live for 4-5 years.
  • Bats have sensitive eyes and can see in monochrome to find prey undetected at night.
  • They use echolocation to identify objects, producing sound waves from the nose or mouth at frequencies that are outside the human hearing range. The sound bounces off objects and back to the bat to help them navigate.

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