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98 million bat calls, 217 terabytes, and a job that would have taken 30 years by hand

Qurexa Editorial Team1 November 20265 min read 0 0
98 million bat calls, 217 terabytes, and a job that would have taken 30 years by hand

What happened

Britain's largest ever woodland bat survey has reported its results, and the headline number is 98 million bat calls. The National Woodland Bat Survey ran from 2021 to 2024. Recorders were left out in English woodlands overnight, listening. In total they collected 9,734 nights of recordings. That produced 217 terabytes of audio, roughly 90,000 hours of sound. Across the programme, around 310 woodlands in England were sampled. The survey was run by the Bat Conservation Trust and Forest Research, funded through Defra as part of the Natural Capital and Ecosystem Assessment programme. The part that made it possible was the software. Researchers used open-source artificial intelligence to sort and classify the calls, with experts checking the results. Scientists estimate that sorting that volume of recordings by hand would have taken more than three decades. The results were published at the end of October 2026, and the data are publicly available through the National Woodland Bat Survey Data Explorer.

Why this matters

Bats are difficult to count. They are small, they are nocturnal, and most of what they do is inaudible to us. Traditional surveys involved experts standing in woods at night with detectors, which is slow, expensive and limited to wherever a person could be. That matters beyond bat enthusiasm. All British bat species are legally protected. Bats are also used as an indicator species, meaning their numbers tell you something broader about the health of a habitat. If you want to know whether a woodland is doing well, bats are a reasonable thing to ask. Until now, nobody had a national picture of woodland bats at this scale. Planning decisions, forestry management and conservation funding were being made with patchy information. There is a wider point here too, and it is a more cheerful one than most AI stories. Nothing about this project replaced a human job. The bottleneck was never a shortage of people willing to study bats. It was that 90,000 hours of audio is more than a career's worth of listening. The technology did a thing that otherwise simply would not have been done.

What the evidence actually says

The survey detected every bat species or species group found in Britain, with one exception: the serotine. That is not because serotines are absent. It is because they are hard to identify reliably from acoustic recordings alone, which is an honest limitation of the method rather than a finding about the animals. Rarer species did turn up. The grey long-eared bat and the barbastelle were both recorded. Barbastelle activity hotspots were concentrated in south-west England. A note on the numbers, because sources differ slightly. Reports give around 310 woodlands in total across the programme, while Forest Research describes sampling up to 210 one-hectare National Forest Inventory woodland sites in England each year. These are compatible rather than contradictory: different sites were sampled in different years, so the annual figure and the programme total are not the same thing. It is also worth being clear about what acoustic data can and cannot tell you. Counting calls is not the same as counting bats. One very active bat can generate a great many calls. The survey measures activity and the presence of species, which is genuinely useful, but '98 million calls' is not '98 million bats' and the researchers do not claim it is. Finally, the classification was AI-assisted, not AI-only. Expert verification was part of the process. The published dataset also includes unvalidated automated identifications, which is normal, and is flagged as such.

Practical advice

Most of us are not going to survey a woodland, but there are a few genuinely useful things here. You can look at the data yourself. The National Woodland Bat Survey Data Explorer is public. If you are curious which bats have been recorded near you, it is there to browse. If you have bats at home, know the law before you act. All UK bat species and their roosts are protected. That includes roosts in lofts, even when the bats are not there. Work on a roof, loft insulation or a barn conversion can all be affected. Get advice before starting rather than afterwards. If you find a grounded or injured bat, do not handle it with bare hands. The Bat Conservation Trust runs a national bat helpline that will tell you what to do. Use gloves and a box, and call them. If you want to help bats in a garden, the useful things are unglamorous: leave some areas untrimmed, avoid insecticides, plant night-scented flowers to attract the insects bats eat, and keep outdoor lighting low and directed downwards. Bright security lights are genuinely disruptive to feeding and commuting routes. If you are interested in volunteering, bat groups exist across the UK, including in Lincolnshire, and most welcome beginners. Acoustic surveying has made this far more accessible than it used to be.

What to know

The National Woodland Bat Survey, run by the Bat Conservation Trust and Forest Research with Defra funding, recorded around 98 million bat calls across roughly 310 English woodlands between 2021 and 2024. It gathered 9,734 nights and 217 terabytes of audio, about 90,000 hours. Open-source AI classified the calls, with expert checking. Doing it manually would have taken more than 30 years. Every British bat species or species group was detected except the serotine, which is hard to identify acoustically. Rare species including the grey long-eared bat and barbastelle were recorded, with barbastelle hotspots in south-west England. Call counts measure activity, not individual bats. The data are public. Sources: Bat Conservation Trust, 'AI reveals 98 million bat calls in Britain's largest woodland bat survey', October 2026, https://www.bats.org.uk/news/2026/10/ai-reveals-98-million-bat-calls-in-britains-largest-woodland-bat-survey; Forest Research, 'The NCEA National Woodland Bat Survey', 2026, https://www.forestresearch.gov.uk/research/the-ncea-national-woodland-bat-survey/; Forestry Journal, 'AI-powered survey detects 98 million bat calls in woodlands', 30 October 2026, https://www.forestryjournal.co.uk/news/26686033.ai-powered-survey-detects-98-million-bat-calls-woodlands/ This article is for general information and does not replace advice from a doctor, pharmacist or other qualified healthcare professional.

#artificial intelligence#bats#conservation#Forest Research#woodland#Defra

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