Validating Airborne eDNA Using Manual Surveys, Acoustic Monitoring and Camera Traps to Detect Birds and Mammals in an Agroforestry Setting

Global loss of biodiversity prioritizes the need for comprehensive and effective biomonitoring methods. Airborne environmental
DNA (eDNA) has shown promise for monitoring terrestrial vertebrates but has not yet been rigorously compared to established
biomonitoring methods. In a field-study in the Netherlands, this study aims to compare species detection from airborne eDNA
with manual surveys, camera trapping and acoustic monitoring, focusing on birds and mammals. Monitoring was performed
over the course of 4 weeks within an agroforestry ecosystem. Birds were monitored using eDNA, manual surveys and acoustic
monitoring, while eDNA and camera trapping were used for mammals. This resulted in four mammal species, detected by both
camera traps and eDNA, while eDNA identified an additional 16 species, primarily small-bodied, including two invasive species. A total of 74 bird species was detected, with varying degrees of overlap between methods and all three methods detected unique species. All but three bird and four mammal species detected were consistent with known occurrences near the study site. Rarefaction curves show that eDNA has the highest potential species diversity, but manual surveys are most efficient when limited time is available. Unique species can largely be explained by method characteristics or limitations; acoustic monitoring detections are limited to species that make sound, while eDNA requires further research on detection range and sensitivity. Our results indicate that for the studied agroforestry system, acoustic monitoring and airborne eDNA can detect a large proportion of birds and mammals detected by manual surveys, in addition to a range of species undetected by the latter, attesting to their effectiveness as biodiversity monitoring methods. This is the first study to compare airborne eDNA with manual surveys and acoustic data, further confirming the high potential of airborne eDNA for biodiversity monitoring.