AI-assisted survey maps rare bats across English woodlands

What you need to know

• Forest Research reports that the survey covered 310 English woodland sites, producing more than 98 million calls and 217 terabytes of audio. An earlier technical document gives different totals, so the figures should be read alongside that unresolved discrepancy. 14
• The recordings included the UK Red List species barbastelle and grey long-eared bat, as well as near-threatened Nathusius’ pipistrelle and Leisler’s bat. The serotine was not detected, although the release says it is particularly difficult to identify acoustically. 1
• The survey reported barbastelle activity hotspots across southern England, with detections in parts of Cornwall, Devon and Dorset where records had been sparse. Common and soprano pipistrelle activity was generally highest in western regions. 1
• Automated BatDetect2 classifications were supplemented by manual review of species presence at each NFI square. A sample of calls was checked further to adjust activity indices for classification error, and the government data record advises users to consult supporting limitations documentation. 2
• Forest Research says the survey provides national-scale monitoring away from known roosts for seven listed bat species. It is also the only active national-scale monitoring in England for barbastelle, Leisler’s bat and Nathusius’ pipistrelle. 1

Why this matters

Acoustic monitoring at this scale adds information about bat presence and activity beyond known roosts, including for species with sparse previous records. That can strengthen the evidence available for future monitoring, but the survey is a baseline rather than a measure of population recovery. 13

What happens next

Repeated survey cycles will be needed to establish whether the baseline can reveal trends over time. Users also need to consult the limitations documentation, particularly when interpreting non-detections and acoustic classifications. 23

What we know

• The survey covered English woodland from 2021 to 2024 and recorded more than 98 million calls, according to the latest Forest Research release. 1
• The dataset combines automated call classifications with manual review and further checks on a sample of calls. 2
• The published findings include records of rare and threatened species and describe regional patterns in bat activity. 1

What we don't know

• The reviewed sources do not reconcile the latest report of 310 sites and more than 98 million calls with an earlier document reporting 319 unique NFI squares and more than 93 million calls. 14
• It is not yet clear how many repeated survey cycles will be needed before the baseline can establish population trends. 3
• The sources do not establish how non-detections should be interpreted for each species, particularly where acoustic identification is difficult. 12

Read the reporting

This WildNews briefing synthesises and summarises reporting from the sources below. WildNews did not produce the original reporting. Learn more about how we use AI