Can citizen science provide a solution for bat-friendly planning?

Bats generally respond negatively to urbanisation, so understanding the impacts of planned developments on bat populations is of great importance. UK bat populations receive protection under national and European law, and sites at which new developments are planned need to be surveyed for bats and the potential impacts assessed. If planning permission is granted, mitigation measures must be taken to provide for the loss of roost sites and foraging habitat.

There is a lack of data on the distribution and activity of many UK bat species. This limits the opportunity to account for these species early in the planning process, and to implement effective mitigation measures. A particular problem is that traditional survey methods, such as roost counts and capture surveys, cannot be scaled up to a countryside level. An additional approach, documented in this paper, indicates that data collected through the use of citizen science could address this, delivering information earlier in the planning process and which better informs decisions on where to target mitigation measures.

The Norfolk Bat Survey has been collecting information on bats within the county since 2013, using a network of passive acoustic detectors deployed across 6,145 sampling locations by volunteers. The resulting sound files are then analysed using an acoustic classifier, which compares these recordings against an extensive library of known species recordings, to assign a species identification and associated confidence score. The species identification of a random sample of the recordings is also assessed manually which provides an additional independent assessment of error in species identification, which is used with the confidence score to allow a more robust identification certainty value to be assigned to each recording in the whole dataset.

BTO researchers were able to use this amazing dataset to quantify the potential effects of future urbanisation within Norfolk, producing maps showing high and low risk areas to bats from urbanisation, together with other areas that offered the best opportunities for habitat mitigation. The latter ‘opportunity maps’ were focused on woodland, wetland and grass/heathland habitats because these are already being used by Norfolk County Council as a set of strategic Green Infrastructure corridors, for targeting delivery of work and for helping to mitigate the impacts of development on sensitive sites.

Additionally, the researchers were able to use the identification certainty assigned to each recording to evaluate the effect of uncertainty in species identification on the risk and opportunity maps. They found that after calls with an identification certainty value below 50% were removed, identification uncertainty made only a small difference to the final risk and opportunity maps. This is important, because it means that robust risk and opportunity maps can be produced, whilst also minimising the work needed to manually assess species identifications.

The value of the urban risk maps delivered through the work is highlighted by its application to existing planned housing development within Norfolk, revealing that while two thirds of the planned developments fall within low risk areas, the remainder fall in medium and high risk areas. Both the risk maps and the opportunity maps have particular value for guiding decision-making at the early stages of the planning process, and should be viewed as complementary to the detailed bat surveys carried out during later stages of the planning process. Importantly, the work demonstrates the value of this approach and its potential with regard to other taxa. It is of particular relevance to passive acoustic data, where there is uncertainty in species identification. The approach is only possible because of the use of volunteer ‘citizen scientists’ who deploy the detectors.