Bat Surveys and Mitigation
Bats inhabit a wide range of structures including buildings, trees, caves and bridges, amongst others. If there is a potential that bats are present on the site of a proposed development, then by law, an appropriate level of survey is required. There are a variety of surveys that Wildscapes ecologists can undertake depending on the type of project and time of year.
All bats and their roosts are protected under The Wildlife and Countryside Act 1981 (as amended) and The Conservation of Habitats & Species Regulations 2017 (as amended).
In England, Scotland and Wales it is illegal to:
There are 18 species of bat in the UK. Bats are protected due to a steady decline in numbers largely as a result of lost habitats and the conversion of buildings that are typically used by bats such as barns.
A bat survey will usually be advised by a planning consultant or architect for works or developments going through a planning application. It may also be recommended following a preliminary ecological appraisal.
As bat surveys are seasonal and mitigation measures can take some time to implement, it is important that bat surveys are conducted as early as possible in the development and planning process.
A Preliminary Roost Assessment (PRA), sometimes referred to as a daytime bat survey or bat scoping, is the first step in the process and should be conducted on any building or structure that will be impacted by the proposed works. A PRA is designed to look for evidence of the presence of bats and determine the suitability of a structure to support roosting bats.
The survey involves an Internal and External Visual Inspection (IEVA) of the building or structure and can be undertaken at any time of year. However, the level of visual evidence created by target species (bats and birds) may vary throughout the year due to weather conditions and human disturbance.
A Preliminary Roost Assessment will typically also include a desk study, where existing information and ecological records pertaining to the site and its surroundings are collated and reviewed.
The survey aims to identify the overall suitability of the site for bats and assess whether further bat activity surveys will be required.
A ground level roost assessment is undertaken on each tree (or group of trees) and this involves the assessment of a tree from the ground to search for Potential Roost Features (PRF). An endoscope is used by a suitably licenced ecologist to view any cavities which are accessible from ground level. A torch and binoculars are also used to assess the canopy branches and upper canopy. Any signs of bat activity such as staining are recorded. If Potential Roost Features are identified or if the tree is difficult to assess from ground level, then an aerial inspection will be conducted.
The Wildscapes climbing team are all City and Guilds NPTC certified in tree climbing and aerial rescue. During an aerial risk assessment, a licensed ecologist will access the upper branches of the tree using a rope and harness to further assess any Potential Roost Features which have been identified from the ground. A torch and endoscope are used to determine if bats are present and to confirm the feature suitability.
Should any proposed works be likely to affect trees which have been assessed to have bat roost potential during the aerial assessment, they are then subject to nocturnal presence/absence surveys.
Often referred to as presence/absence surveys or emergence/re-entry surveys, these are required if the Preliminary Roost Assessment has identified bats (or the potential for bats). The surveys take place at dusk and dawn and involve surveyors observing the building, tree or structure from vantage points. The aim is to determine the presence or likely absence of a bat roost within a structure and any necessary mitigation requirements.
Any bats seen to be entering or leaving the features are recorded. In addition, surveyors record any other bat activity detectable from their survey position. Where possible, the time of recording, species, the number of bats, type of activity, and flight path of observed bats are recorded. Bats entering or leaving a building or tree are considered evidence of bat roost presence within that entity.
Nocturnal Bat Surveys are highly seasonal and typically undertaken by Wildscapes ecologists from May to September in weather conducive to bat activity, i.e. little or no rain, low wind and temperatures above 10°C. The number of surveys required (between 1 and 3) is determined during the Preliminary Roost Assessment and is dependent on the overall suitability of the site for bats.
To determine the value of a site for foraging and commuting bats, bat activity surveys can also be undertaken. These involve a combined approach of installing static board-band detectors on site and conducting transects surveys of the site and the surrounding area. During the survey, surveyors walk a predetermined transect route to identify habitats or features of importance to foraging, commuting and roosting bats. A transect survey should be carried out monthly between May and October.
If a bat activity survey highlights the presence of roosting bats within a structure and the development cannot be altered to prevent any impact on the species, then appropriate mitigation will be required. Work is typically unable to proceed until a European Protected Species Mitigation Licence (EPSML) is granted by the relevant statutory body. Our experienced ecologists can guide you through this process and apply for the necessary licences on your behalf.
Where the conservation importance of the roost is assessed as low following bat activity surveys and the impact of the development on bats can be easily mitigated, it may be possible to utilise a more simplified system and apply for a Bat Low Impact Class Licence. Again, Wildscapes ecologists will advise if this is a suitable option.
Mitigation strategies vary and can take the form of the installation of several bat boxes through to the design and construction of a specific roof feature for roosting bats. The aim is to ensure there is no detrimental effect on the bats, and strategies will be proportionate to the number of bats identified and the conservation value of the species.
Once the necessary licence has been granted, Wildscapes can offer a suitably qualified ecologist to act as an Ecological Clerk of Works (ECoW), providing supervision during the construction phase of the works and ensuring the specified mitigation measures are implemented.
