Abstract
Songs of Phylloscopus c. castaniceps were examined at different elevations to understand how vocal behaviour and environmental factors shape song structure and diversity. Acoustic data were collected from multiple locations across Southeast Asia over a range of altitudinal bands between 2021 and 2023. Annotated song recordings (n=134) were used to extract metrics and analyze the Song Richness Index (SRI) and maximum frequency (Fmax) for each song. These metrics were analyzed using the Kruskal–Wallis nonparametric test, followed by post hoc pairwise comparisons using Dunn’s test.
The findings revealed greater verse variation but lower song richness at lower elevations, likely due to competition for acoustic niches. Higher elevations, by contrast, showed higher song richness but fewer within-verse variations, indicating that minimal verses may be favoured in settings with fewer competitors. This pattern suggests that environmental factors exert strong influence on auditory cues. Additionally, the results showed significant variation in Fmax across different elevational bands (χ2(2) = 196.87, P = 1.78 × 10-43), suggesting that elevation-related environmental conditions affect song characteristics and transmission. Elevation and song richness were also positively correlated (χ2(3) = 77.84, P = 8.91 × 10-17), supporting the hypothesis that bird songs become more complex and diverse at higher elevations. Overall, these results demonstrate how environmental conditions shape song diversity in P.c. castaniceps, validating the acoustic niche hypothesis and highlighting the importance of incorporating altitudinal gradients into avian bioacoustics research.
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