What you need to know about bat surveys

Common Pipestrelle

Why are bats protected?

Bat populations across the 18 native species in the UK have been in decline over the last 50-100 years due to increased development. 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. Harming or disturbing bats is a criminal offence and anyone seeking planning permission to develop buildings or sites involving trees or potential roosting sites, has a legal obligation to avoid disturbing bats. It is illegal to:

  • Intentionally kill or injure bats
  • 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

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 (or Scoping Bat Survey) (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 statutory nature conservation bodies Natural England, Natural Resources Wales and NatureScot. The length of time that a bat survey is valid for depends on the local planning authority, but all are valid for 12 months and they usually extend for up to 24 months.

What is a bat roost?

It is a feeding or resting place which can be in caves, tree cracks, lofts, barns or under loose or hanging tiles. 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 day roosts, transitional roosts, feeding roosts, hibernation roosts and maternity 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.

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 Assessment (PRA) or Scoping Bat Survey (stage 1)

This is an internal and external inspection of buildings which can be carried out at any time of year. The aim is to exclude the following three factors which trigger a further survey:

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

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

Bat Emergence and Re-entry Survey (BERS)

Carried out following a PRA survey which has established that there are bats present, or that there are roost features which they could use, this survey is the second phase of the initial assessment process. A bat surveyor will visit the site and monitor potential bat entry and exit points to gather data, using equipment such as bat detectors, infrared lights, night vision and thermal imaging cameras along with detectors which convert echolocation calls into an audible readout. Bat species have different calls so this can help with identification.

The findings and recommendations, along with details of the effect that the proposed development would have on the bats, form the basis of this further survey. It will also contain mitigation measures to enable the application to progress, along with details including the type of roost, species and bat numbers.

Bats hibernate in winter as there are less insects for them to feed on, so BERS 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. Some local planning authorities will accept surveys done in the sub-optimal weeks in April and September/October providing that weather conditions are suitable.

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 obtaining planning consent. The number of bat surveyors and site visits required by a BERS depends on the PRA results.

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.

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, a 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.

Noctule Bat

Bat mitigation

The bat surveys collate data to establish:

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

Having gathered this information, a surveyor 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.’ 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 dynamic and therefore a survey may still be required.

Four Pipestrelles in a church tower

How to get a bat survey

To start a bat survey, you need to contact a suitably qualified ecological consultancy like Arbtech. They will be able to tell you what is required and when the survey will be done. Getting in touch with an ecological consultancy early on is recommended to reduce the chances of delaying your project.

Survey costs:

A Preliminary Roost Assessment costs from £299 + VAT. An Emergence Survey costs £789 + VAT

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 UK bat species 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 species, having a wingspan of 22cm. They have a brown back with lighter colouring on their stomachs and a dark face.
  • The largest UK bat species 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 maternity roosts 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 which are outside the human hearing range. The sound bounces off objects and back to the bat to help them navigate.

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