Common cuckoo vocalisations as an indicator for the avian diversity – A study with passive acoustic monitoring

Surrogate species are often used to represent broader groups in conservation and research. However, whether a single species can truly reflect an entire ecosystem remains debated. The common cuckoo (hereafter cuckoo) Cuculus canorus has been suggested several times as an indicator of biodiversity with various outcomes. In this study, we utilised passive acoustic monitoring to record 48 soundscapes within a farmland area in Poland, aiming to assess the relationship between cuckoo vocalisations and bird species richness. We employed automated software for cuckoo vocalisation detection and manually analysed 10-minute samples from each site to determine species numbers. Additionally, we used BirdNET, an automated recognition algorithm, on 8-hour recordings to compare species composition with results obtained manually. We also utilised acoustic indices to evaluate their reflection of overall species richness. Our results revealed significant differences between manual and automatic species detection methods, with BirdNET detecting twice as many species as human observers. Furthermore, we noted more cuckoo vocalisations at sites with elevated bird species and host richness obtained automatically, indicating its potential as a biodiversity surrogate. However, acoustic indices failed to mirror acoustic diversity in the farmland habitat, showing unified values across all sites. These findings highlight the necessity of enhancing monitoring approaches to ensure a more comprehensive depiction of avian diversity, thus strengthening conservation measures.