Bat Surveys of Buildings and Structures

bat surveys of buildings and structures

B.A.T. Ecological specialises in undertaking comprehensive bat surveys of buildings, including those of cultural and historical importance such as churches and those with heritage listed status, as well as other complex structures and underground sites. B.A.T. Ecological reports are clear, concise and will stand-up to scrutiny, and include evidence-based conclusions and recommendations tailored to your project.

Please get in touch if B.A.T. Ecological can help you and your project with any bat surveys, reporting, licensing, or mitigation / compensation design and implementation - info@bat-ecological.co.uk | +44 (0) 7870 157022.

Bat surveys of buildings, built structures and underground sites are required wherever development or renovations could affect bats or their roosts. Most often, bat surveys and a report are required to support a planning application or for Listed Building Consent (or Faculty Consent for churches); however, good practice (to minimise the risk of committing a legal offence) is to undertake bat surveys prior to any renovations of buildings or structures that support features where bats are reasonably likely to roost - Potential Roost Features (PRF) - irrespective of whether formal consent is required.

Bats are opportunists and could roost almost anywhere. The places where they are most often found within buildings, however, are: apertures beneath and between roof tiles, ridge tiles, and lead flashing; cavities in masonry and between masonry and wood; accessible soffit boxes and roof voids; gaps behind cladding, bargeboards, hanging tiles, and fascia’s; and apertures around window and door frames including those associated with lintels. Bats can then also be found roosting or hibernating in cellars, culverts, tunnels, bridges, old walls, ice houses and grottos, as well as caves and mines.

Bat surveys of buildings, built structures and underground sites usually start with a preliminary daytime roost assessment, which should always be conducted by an appropriately licensed bat ecologist if the professional surveyor is intending on inspecting any features that could support bats with a torch or endoscope. A preliminary daytime bat survey visit by a licensed bat ecologist has several aims but the main objectives are: a) to assess the overall suitability of the building or structure for bats (usually in line with the current survey guidance); b) to identify any features that roosting bats could exploit; and c) to conduct a search for any evidence of bats in accessible areas.

It is important to note that the absence of bat evidence does not necessarily equate to evidence of bat absence because in many situations it is not possible to inspect all locations where bats could roost within a building or structure, especially those at height. Bats can squeeze into apertures of less than 15 mm, and they can also occupy buildings and structures for different purposes at different times of year, including only transiently.

In achieving the objectives above an experienced surveyor (provided with sufficient site access) will be able to determine one of the following from a preliminary roost assessment:

• whether bats are present - if evidence is apparent;

• whether bats are reasonably likely to be present - if no evidence of them was identified but there are places where they could reasonably roost; or,

• whether the likelihood of bats being present is nil or negligible - because there was no evidence of them and there are no places where they could roost, or there are a few places where they could theoretically roost but they are unlikely to use them in practice.

If an experienced, licensed bat surveyor assesses the likelihood of bats being present in a building or structure as nil or negligible, then further surveys are not required; however, if bats are present, or could reasonably be present, then further surveys are usually necessary before the applicable consent/s can be issued.

Further surveys usually comprise summer nocturnal surveys - see below - but might comprise further daytime surveys including hibernation surveys. Bats are more vulnerable to disturbance during their winter hibernation period and as such additional training and experience is required to undertake hibernation surveys - a Level 2 (CL18) Natural England bat survey licence (or CL19 or CL20) is required.

Nocturnal bat surveys of a building or a structure are usually required for two main reasons: to determine the presence or likely absence of roosting bats with sufficient confidence to support a planning application, for example, because this cannot reasonably be determined from a daytime survey; or, to understand more about a known bat roost for planning and licensing purposes.

Nocturnal bat surveys usually comprise evening emergence surveys. The optimum period for undertaking nocturnal bat surveys is mid-May through mid-August, however, sometimes early May and late August into early September can also be suitable, and within a wider suite of surveys or if surveying for certain roost types or bat activity April and mid-late September can be acceptable.

Nocturnal bat surveys need to be conducted in mild (>10 degrees), calm, and dry weather to be robust, with a sufficient number of vantage points around a building or structure to cover all features that could be used by roosting bats

When a bat roost hasn’t been identified from a preliminary roost assessment, but several PRF have been identified and the building or structure has been assessed as being reasonably likely to support bats, then the level of nocturnal survey effort required will reflect the overall potential suitability of the building or structure as assessed by the surveyor. Typically, in line with current guidelines, a building with low potential suitability for roosting bats will require one emergence survey, a building with moderate potential suitability will require two separate surveys, and a building with high potential suitability will require three separate survey visits. The current survey guidance that relates to this is provided on page 44, Table 4.1 here.

Pre-dawn surveys are not very reliable to determine the presence or likely absence of roosting bats. These surveys may, however, be useful to help characterise an identified roost - see below - and to fully understand how bats use a structure (e.g., bats sometimes return to a building before dawn via different routes to how they exit it at dusk) especially within a wider suite of nocturnal surveys.

Nocturnal roost characterisation surveys are usually required if there is a known bat roost because Local Planning Authorities and the Statutory Nature Conservation Body (e.g. Natural England) need information on the species and type of roost present (e.g. maternity, mating, hibernation, transient), as well as how the bats use it, when considering whether to issue planning consent or a development licence respectively. At least two separate nocturnal surveys are usually required when a bat roost has been confirmed, often three, and they need to be appropriately timed through the summer.

B.A.T. Ecological has always undertaken and continues to undertake nocturnal bat surveys using modern, high specification infra-red (IR) and thermal imaging (TI) technologies - often referred to a Night Vision Aids (NVAs) - to augment surveyor observations.

Please contact me if you need help with any of the above regarding buildings or structures, or any related bat licensing or mitigation / compensation design and implementation: info@bat-ecological.co.uk | +44 (0) 7870 157022.