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Abstrakt

Species determination of forest birds in the field is mostly acoustic-based. Thus, acoustic detectability of birds is probably a key factor significantly affecting the results of bird census in forests. In this study, we focused on acoustic detectability of nesting birds in the European temperate floodplain forest. We analysed songs in passerines and territorial calls in non-passerine birds. The audibility of bird calls is relatively high, most species can be well acoustically detected at the distance of 100 m and longer. Good audibility was recorded (across the species under study) at the distance of 57–608 m (mean 213 m, median 175 m, SD = 117, n = 53), threshold audibility at the distance of 57–897 m (mean 231 m, median 185 m, SD = 151, n = 53). In a floodplain forest with closed canopy, the audibility of birds was significantly lower than in open habitats. The audibility of birds was rather low before 10 a. m. (Central European Summer Time) and increased later due to the decline of vocal activity of a part of the bird assemblage, when a smaller number of individuals was calling and, at the same time, the threshold distance of their audibility increased. The audibility is higher in species with larger body size (body mass > 50 g) in comparison with smaller species (body mass ≤ 50 g). In the paper, some factors affecting the acoustic detectability of forest birds are discussed.