Practical techniques: Bats
UK and Ireland
There are 18 species of bat in the UK, which accounts for a quarter of all mammalian species. Ten of these same species are found in Ireland. All the British and Irish bats are nocturnal, spending daylight hours in roosts before emerging at night to forage for insects. They hibernate during the winter in hibernation roosts and the females gather in maternity roosts during the summer months to have their young. A variety of other types of roost are used by bats during different seasons and by male bats roosting alone. Bats may roost in a range of environments, both man-made and natural places, including houses, bridges, caves, mines and trees. Some species are almost entirely dependent on man-made structures, while others roost almost exclusively in trees. They forage in areas rich in insects and may change roosts within their home range.
Protection and its implications
All species of bat and their roosts are fully protected under the Habitats Directive and the associated Regulations in the UK and Ireland. In England and Wales, there is also some additional protection against disturbance and obstruction from a structure they use for shelter or protection from the Wildlife and Countryside Act 1981. In Ireland, bats are also afforded protection under the Wildlife Act, 1976, as amended in 2000. As a result of their full protection under the Habitats Directive, some mitigation on development sites for bats is governed by a strict licensing procedure, administered by the appropriate statutory agency. A licence will be required whenever disturbance of bats or damage to their roosts is likely to occur. The protection of bat roosts applies even if no bats are present at the time of development.
More about licensing for European protected species.
Seven species of bat (Barbastelle, Bechstein’s, greater and lesser horseshoe, brown long-eared, noctule and soprano pipistrelle) are priority species in England and Wales, nine species of bat (Brandt’s, Daubenton’s, whiskered, Natterer’s, noctule, Nathusisus’s pipistrelle, pipistrelle, soprano pipistrelle and brown long-eared) are priority species in Scotland and three species of bat (Nathusisus’s pipistrelle, common pipistrelle and brown long-eared bat) are priority species in Northern Ireland Priority Species list. In Ireland, nine species of bat (Daubenton’s Whiskered, Natterer’s Leisler’s Natusius’ Pipistrelle, Soprano Pipistrelle, Common Pipistrelle, Brown long eared and Brandt’s bat) are listed on the All-Ireland Species Action Plans for bats.
In common with most protected species, the presence of bats can lead to planning permission being refused unless the applicant can clearly demonstrate that they will be protected during the development, that disturbance is kept to a minimum and adequate alternative habitat is provided to sustain at least the existing population. As bats are European protected species, it will also be necessary to demonstrate that the tests in the Habitats Directive can be met at the planning application stage.
Bats roost in buildings, including occupied houses, trees, bridges and underground structures such as caves and mines. Occasionally, buildings supporting a bat roost require demolition, or trees which support a bat roost must be felled. In these circumstances various levels of mitigation will be required by the relevant statutory agency, depending on the type of roost and the numbers and species of bat using it. For example, more mitigation and monitoring will usually be required when development affects a roost used for breeding by a rare species of bat than when development affects a roost used occasionally by small numbers of a common species of bat. When roost interference is unavoidable, the developer has to demonstrate that there is no satisfactory alternative and that they will be no detrimental effects for the species concerned.
The foraging habitat of bats is not directly protected in the same way as their roost sites. However, the planning policy that protects bats may extend to cover bat foraging habitat. Should a roost site also be affected by the development, then maintaining the bat foraging habitat is likely to be a condition of a European Protected Species licence.
Mitigation should be site specific as the mitigation requirements will differ from site to site. When a bat roost is affected by development, by far the best option is to avoid disturbing the roost and plan work for a time when bats are absent. For example, a building used as a maternity roost in summer may not be occupied by the bats in winter and so the winter months would be the best time to undertake works affecting the roost. For roost sites used on an occasional basis by bats, it may be possible to simply check that bats are absent just before the works take place, although a licence is still likely to be required.
Undertaking works while the bats are in occupation of the roost is problematic. One approach for roosts that do not contain dependent young might be to provide the bats with an alternative roost site nearby.
When a roost site is simply being modified, for example a barn conversion or building renovation, it may be possible to do the work while bats are in occupation by phasing the work and using a system of screens to separate the bats from the construction work.
A precautionary approach should be adopted when demolishing buildings or felling trees which may harm bats. This involves dismantling the building or tree section by section, under licence, and checking carefully for bats as the work progresses. The sections of building or tree are then left intact overnight to give any bats hidden in crevices an opportunity to escape unharmed.
Maintaining habitats for bats
There are a variety of ways to accommodate roosting bats within new developments. These include:
- retaining existing bat roosts by preserving trees and buildings used by bats
- creating bat roosting spaces within converted barns and renovated houses which are separated from the living space
- incorporating bat roosting spaces within the structure of new buildings which bats can access via a special bat brick or modified roofing tile
- providing bat boxes on the outside of new buildings or on trees
- constructing a purpose-built bat barn or bat tower located away from the new buildings.
There are several types of bat box and roosting space which are commercially available and simple to install. However, a bat barn requires careful design and because of its size may also need planning permission before it can be constructed. Bat barns and some types of bat boxes are heated to increase their attractiveness to bats. In many cases, it will be necessary to ensure that replacement roost sites are in place before any existing roosts are lost. For rarer species of bat, it will usually be necessary to demonstrate that the bats are using the new roost before the existing roost is lost. This could take more than a year.
Bats forage anywhere that there is a rich supply of their insect food. Features such as hedgerows, trees, woodland, flower-rich grassland and ponds incorporated within the design of the development should benefit bats and it is essential that these features are at least near to the site in order for the roost creation described above to have a chance of success (see Biodiversity for Low & Zero Carbon Buildings: a technical guide for new build, 2010). Linear features such as hedgerows are important for bats to navigate their way around their home range. Maintaining or creating alternative links between hedgerows within and outside the development site can therefore be important. This may be particularly so when hedgerows connect a roost site with an area of important foraging habitat. Ecologists often refer to linear features used by bats in this way as commuting corridors.
The statutory agencies in the UK and Ireland may require licensed, post-development monitoring. The length of the monitoring period and the intensity of the monitoring activity is dependent on the type of roost and the species affected. As an example, a maternity site for more common species of bat affected by development is likely to require 2 years or more of monitoring visits to check that the mitigation has been successful. The relevant statutory agency is likely to require that a report on the monitoring activity is provided at the end of the monitoring period.
Timing of works
The best timing of works involving bat roosts (under licence) depends on the type of roost in question. The following timings apply to the four major roost types:
- Maternity and summer roost sites: Between October and May
- Hibernation sites: Between May and October
- Mating and swarming sites: Between November and August
- Roosts occupied year round: March to May or September to October
Mitchell-Jones, A.J. (2004) Bat mitigation guidelines. English Nature, Peterborough.
Mitchell-Jones, A.J. & Mcleish, A.P. (2004) Bat Workers’ Manual. JNCC, Peterborough.
Bat Conservation Trust (2007) Bat Surveys – Good Practice Guidelines. BCT, London.
Williams, C (2010) Biodiversity for Low & Zero Carbon Buildings: a technical guide for new build, RIBA.
Kelleher, C & Marnell, F (2006) Bat Mitigation Guidelines for Ireland. Irish Wildlife Manuals, No. 25 National Parks and Wildlife Service, Dept. of Environment, Heritage and Local Government, Dublin.
Natural England (2015) Bats: surveys and mitigation for development projects. https://www.gov.uk/guidance/bats-surveys-and-mitigation-for-development-projects