The largest passive acoustic bat survey ever conducted in Britain has detected over 98 million bat calls across 310 woodland sites. The National Woodland Bat Survey, a collaboration between Bat Conservation Trust (BCT), Forest Research, and funded by the UK Government, collected acoustic recordings between 2021 and 2024.
Results underscore the critical role of woodlands, especially broadleaved ones, for bats. Woodlands provide essential foraging, roosting, and movement habitats for all British bat species. Common pipistrelles were found in all 310 surveyed woodlands, with soprano pipistrelles at 99% of sites, Myotis bats at 98%, noctules at 94%, and brown long-eared bats at 90%.
Dr Chloe Bellamy, Senior Spatial Scientist at Forest Research, stated: "By harnessing AI technology, we have produced one of the most comprehensive datasets ever assembled on bats in England’s woodlands. This extraordinary data will improve how we create and manage woodland, to support bat populations and wider nature recovery."
The survey processed approximately 90,000 hours of audio data, made feasible by AI advancements. Researchers from the University of Edinburgh and University College London (UCL) collaborated to develop technology for identifying bat echolocation calls. A subset of these AI identifications was verified by 19 bat call experts from BCT’s Verifier Network.
Every bat species or group found in Britain was detected, except for the less common serotine. Notably, rare and threatened species like the grey long-eared bat, barbastelle, Nathusius’ pipistrelle, and Leisler’s bat were recorded.
Kate E Jones from University College London commented: "AI has fundamentally changed the scale at which we can monitor wildlife. Previously, analysing this volume of acoustic data would simply not have been feasible. These efficient open-source AI tools allow organisations like the BCT to identify millions of bat calls across thousands of nights of recordings, identify patterns and flag species at a national scale, while BCT’s expertise ensures the results can be carefully verified."
This survey establishes a vital baseline for tracking long-term changes in bat presence, distribution, and population trends in English woodlands. For seven species, including greater horseshoe and barbastelle, it provides the only national-scale survey away from known roost sites.
The survey's scale is significant given bats' nocturnal, mobile, and often elusive nature. Acoustic monitoring of echolocation calls offers a richer picture of their distribution and habitat use. Patterns observed, such as common and soprano pipistrelle activity in western regions and barbastelle hotspots in southern England, offer clues for understanding the influence of climate, woodland cover, and habitat connectivity.
Dr Lia Gilmour, Research Manager at Bat Conservation Trust, said: "Bats can indicate the quality of the habitats they rely on for survival... Understanding how bats are faring in woodlands, will allow us to understand how pressures such as climate change and changes in the management of our landscapes may impact these important habitats and how we can best conserve them."
The National Woodland Bat Survey exemplifies how technology can transform wildlife monitoring, enabling analysis on an unprecedented scale through automated acoustic identification combined with expert verification. It also highlights the value of collaboration between conservation organisations, government, forestry researchers, and universities.
David Jones, Senior Responsible Owner for the Natural Capital and Ecosystem Assessment programme, noted: “The National Woodland Bat Survey gives a full picture of bats across England’s woodlands, using technology to analyse millions of recordings at a scale that wouldn’t have been possible by people alone."
Data on species occurrence and activity are available online via the National Woodland Bat Survey Data Explorer.
