Acoustic approach as an alternative to human-based survey in bird biodiversity monitoring in agricultural meadows

considered only songbird species, we found a significant effect of detection method (χ2 = 674.070; p<0.001; df = 3), observer (χ2 = 10.622; p<0.001; df = 1) and no effect of time in a season (χ2 = 1.409; p = 0.235; df = 1) on the number of detected species. The recorder method detected (1) significantly more species (on average 7.67 species) than the observer up to 50 m (on average 1.99 species) and (2) observer up to 100 m (on average 5.39 species) but (3) signifi- cantly fewer species than observer without distance limitation (on average 9.80 species). In the case of farmland bird species, we found a significant effect of detection method (χ2 = 501.075; p<0.001; df = 3), observer (χ2 = 7.774; p = 0.005; df = 1) and time in the season (χ2 = 8.701; p = 0.003; df = 1) on the number of detected species. The recorder method detected (1) signifi- cantly more species (on average 2.90 species) than the observer up to 50 m (on average 1.20 species), (2) significantly fewer species than observer without distance limitation (on average 4.50 species) and (3) a statistically indistinguishable number of species from observer up to 100 m (on average 2.98 species). In the case of meadow bird species, we found a significant effect of detection method (χ2 = 271.605; p<0.001; df = 3) and no effect of observer (χ2 = 0.137; p = 0.712; df = 1) and time in the season (χ2 = 0.024; p = 0.877; df = 1). The recorder detected (1) significantly more species (on average 1.86 species) than the observer up to 50 m

(on average 0.68 species), (2) significantly fewer species than the observer without distance limitation (on average 2.67 species) and (3) a statistically indistinguishable number of species from the observer up to 100 m (on average 1.84 species). Detection rate of common birds During the study 20 bird species were only detected by the human-observer method (three songbirds, two meadow and two farmland bird species; in total 63 detections, from 1 to 13 per species), while five species were only detected by the recorder method (three songbirds, no farmland or meadow species; in total 7 detections, from one to three per species; see S3 and Fig 1. Number of surveys during which particular bird species were detected, independently of the detection method (recorder, observer or both). Graph based on 148 surveys. The most widespread species, European skylark was detected during 132 surveys. https://doi.org/10.1371/journal.pone.0266557.g001 PLOS ONE Acoustic bird biodiversity monitoring in agricultural meadows PLOS ONE | https://doi.org/10.1371/journal.pone.0266557 April 8, 2022 6 / 16