Bats

Bats make the most of the plentiful summer before hibernating during the cold winter, meaning there are limited windows of opportunity to carry out bat surveys to ensure a development is compliant with the law. All bats and their roosts are fully protected by UK law, thus they’re afforded strict protection from the deliberate killing, injuring, disturbing or taking, and their resting places are protected from damage and destruction (including when not in use) under the Habitats and Species Regulations 2017.

Bats: ecology

Bats: Pipistrelle Bat on the side of a building © Oliver Brown
Bats: Pipistrelle Bat on the side of a building © Oliver Brown

Seventeen resident species of bat can be found in the UK, all of which are nocturnal; spending the day resting in roosts before emerging around dusk to hunt. They roost in a range of locations including buildings, bridges, caves and trees, with some species now showing preference to man-made structures.

Bats are highly efficient predators using their eyes, ears and echolocation to forage insects. Their foraging style is diverse and ranges from aerially hawking flying insects from the sky to gleaning them directly from surfaces.

Bats are important to the ecosystem as they control insect numbers, including garden and crop pest species. One of our most numerous species, the common pipistrelle bat, weighs roughly the same as a 20p coin and can eat up to 3,000 insects in one night.

Will bats and their habitat impact my development plans?

Identifying if the land you propose to develop has the potential to support the species, starts with a survey.

Bats: surveys

Bats: A rare Bechstein’s bat caught during the Bat Handling training © Thomson Environmental Consultants
Bats: A rare Bechstein’s bat caught during the Bat Handling training © Thomson Environmental Consultants

Depending at what stage the developer is at in the ecology process, the first thing that is usually carried out is a Preliminary Ecological Appraisal (PEA). This method is to rapidly assess and map habitats on site, highlighting areas for further bat surveys.

Following successful completion of a PEA and its recommendations, bat surveys are conducted by experienced ecologists. If there is potential for bat roosts on a site, the following surveys may be required:

  • Preliminary Roost Assessment (PRA)
  • Preliminary Ground Level Roost Assessment (PGLRA)
  • Tree Climbing Survey
  • Emergence/ Return to Roost Survey
  • Hibernation surveys and advanced bat survey techniques

Bats: PRA and PGLRA

A PRA is conducted for buildings and a PGLRA is conducted for trees – both of which will help to determine their level of potential to support roosting bats. These preliminary surveys can be carried out during the same site visit as the PEA but require in depth knowledge of bat ecology and roosting preference to determine how bats may use a tree or structure throughout the year.

On occasions this may involve the use of high powered torches and endoscopes to investigate potential roosting features. Both these techniques can disturb roosting bats and so therefore are required to be carried out by a licensed bat worker.

Bats: tree climbing surveys

Bats: Ecologist, Amy, during tree climbing training © Thomsonec
Bats: Ecologist, Amy, during tree climbing training © Thomsonec

Tree Climbing Surveys are useful to internally inspect a Potential Roost Feature (PRF) on a tree identified from the ground. The potential assigned from the ground is often reevaluated upon inspection and individual features can have their potential increased.

However, since a high number of features that look promising from the ground lack a suitable internal space for a roosting bat, Tree Climbing Surveys could save on costs by reducing the number of Emergence/ Return to Roost Surveys required, if there are many trees being affected by a development.

Bats: emergence / return to roost surveys

Emergence/ Return to Roost surveys are conducted to confirm the presence or likely absence of roosting bats on a development. For each PRF identified on buildings or trees, either one, two or three of these surveys are required depending on the potential the feature was assigned in the PRA or PGLRA. The surveys are also weather dependent and should be reasonably spread from April to October.

Bats: activity transects and static monitoring

Activity Transects involve walking the site at dusk and dawn to record all bat activity. For larger developments, or developments that may impact bats commuting or foraging habitat, it may be necessary to gauge the impact of the project on bat foraging grounds and commuting corridors.

Static Monitoring involves placing devices with microphones for longer periods out on important linear structures to detect bats, such as hedgerows and tree lines. Both surveys are designed to identify important areas of the site so that suitable mitigation can be advised against any impacts to bats.

Bats: hibernation surveys

Hibernating bats require very specific conditions to keep cool and hydrated during the winter and are also at much higher risk if disturbed at this time of the year. When these conditions are flagged up during a PRA or PGLRA, a hibernation survey will be recommended.

Two visits over the period of January through to February will be scheduled to investigate features in a tree or structure for the presence of hibernating bats. This may also involve the use of static monitoring devices, which can be placed in loft voids or underground cellars to record activity over the course of the hibernating season.

Bats: advanced bat surveys

Where particularly rare or endangered bat species may be roosting and where the impacts of the development may be quite severe, advanced license bat survey techniques may be used to record more in-depth information on bat species diversity and their site usage.

These techniques involve the capture of bats in flight using harp traps and mist nets to identify bats by hand, as well as potentially radio tagging them and tracking their activity and movement through important habitat like mature and ancient woodland.

Since these survey techniques are carried out with a much higher level of risk to the bats’ well-being, they’re usually only used when the data needed for the development goes beyond what other less invasive techniques can record and are only possible with the application of a specific project license from Natural England.

Licensing requirements for bats

If a bat roost is going to be affected by a project, developers will need to apply for a European Protected Species Licence (EPSL) to potentially disturb or destroy a roost, translocate, or exclude roosting bats. This application will describe the details of the roost, and steps that will be taken to provide adequate mitigation.

The Wildlife and Countryside Act 1981 makes it an offence to obstruct access roosts/resting places, as well as protecting the animal from disturbance while it uses this place or structure. For any impacts on bats caused by a development, a license from Natural England must be obtained in order to contravene these laws. One particular project that Thomson has supported in helping developers gain a bat EPSL, is for Basing House, Hampshire.

Bats: mitigation

Bats: Bat box installation on a tree © Thomsonec
Bats: Bat box installation on a tree © Thomsonec

Once surveys have been conducted to determine the presence of bats on site, mitigation measures can be set in place to avoid and/or reduce developmental impact.

This may include the creation of alternate bat roosting sites to replace excluded or destroyed roosts. Bat boxes can be fitted to replace smaller roosting sites, however for more complex situations bat roosts can be integrated into the fabric of proposed built structures, or bat houses can be erected to replicate specific roosting conditions.

When bat habitat is being lost or changed, compensatory features and habitat can be created to encourage foraging and commuting bats. For example, the planting of new hedgerows and tree lines, or ‘dark corridors’ that exclude light over sections of a site.

Lighting can be a sensitive element for bats and extensive research and work has gone into the development and implementation of bat friendly lighting schemes. This involves timed lighting to avoid the most sensitive times of night for bats; light that emit less disturbing wavelengths and as hooded lamps to reduce light spill.

How we can help

We have a team of ecologists experienced in aiding with compliance, license applications and mitigation related to bats. We are adept at using innovative approaches and customising projects to produce the most time and cost-effective solutions. Let us know if your development plans are impacted by the potential of bats.

Arrange a preliminary ecological appraisal with us today

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