Bat Surveys and Mitigation
There are a variety of bat surveys which can be undertaken;
Preliminary Roost Assessment
A Preliminary Roost Assessment or PRA, sometimes referred to as a daytime bat survey or batscoping is designed to determine the suitability of the building to support roosting bats. Our experienced ecologists can typically undertake a PRA for under £300.
The survey involves an Internal and External Visual Inspection (IEVA) of the building or structure. Features such as small gaps in soffit and fascia boards, raised or missing ridge tiles and gaps at gable ends, which have potential as access points are visually assessed by our experienced bat ecologists. The interior of the building including roof voids (where possible) is visually assessed for evidence of bat activity and for its suitability to support roosting bats.
Preliminary Roost Assessments 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 data search with the local bat group or records centre as part of a desk study.
Tree Survey - Ground-Based and Aerial Risk Assessment
The Ground-based Risk Assessment of trees involves the assessment of a tree from the ground to search for Potential Roost Features (PRF). Wildscapes follow the standard guidance for preliminary ground level roost assessment of trees as listed within Bat Surveys for Professional Ecologists Good Practice Guidelines 3rd Edition (Collins.J. (ed.), 2016).
An endoscope will be 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.
Each PRF will be classified into the following categories based upon its likelihood to support roosting bats, the number of bats the feature could support and types of roost likely to use the PRF; Negligible, Low, Moderate, High and Roost present. Each tree is then given an overall classification based upon the PRFs present.
Should any proposed works be likely to affect trees with bat roost potential, they can be assessed by our tree climbing team in an Aerial Risk Assessment.
Our climbing team are all City and Guilds NPTC certified in tree climbing and aerial rescue. A licenced 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's 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.
Nocturnal Bat Survey – Trees and Buildings or Structure
Nocturnal bat surveys are intended to determine the presence or likely absence of a bat roost in a building, tree or other structure (bridges, tunnels etc...). These surveys take place at dusk and dawn and involve surveyors observing the building, tree or structure from vantage points. 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.
Surveyors are equipped with the broad-band bat detectors to allow calls to be recorded and analysed at a later date if required.
Our in house bat ecologists have over 15 years' combined experience undertaking nocturnal surveys on a range of buildings and structures.
Surveys are typically undertaken from May to September in weather conducive to bat activity, i.e. little or no rain, low wind and temperatures above 10°C. Emergence (dusk) surveys commence 15-30 minutes prior to sunset and continue until 1.5 hours after sunset. Return (dawn) surveys commence 1.5 hours prior to sunrise and continue until 15-30 minutes after sunrise.
Bat Activity Surveys
To determine the value of a site for foraging and commuting bats bat activity survey are undertaken. These involve a combined approach of installing static broad-band detectors on site and undertaking transect surveys of the site and the surrounding area.
The data from these surveys are then statistically analysed in various computer packages and GIS to determine which species are using the site and which areas are valuable for foraging and commuting bats.
Bat Mitigation and licencing
Our ecologists have over 15 years’ experience designing bat mitigation and applying for protected species licences. Our consultancy manager holds a low impact mitigation licence for bat, as well as a specialised mitigation licence for churches. We specialise in historic buildings with past experience designing tailored mitigation for churches, barns, and other listed buildings.
Image credit: Paul Liptrot