Noise-induced vocal shifts in the Himalayan Monal (Lophophorus impejanus) vocal distribution in two different habitats

Abstract

Anthropogenic noise, an unexpected consequence of human activities, is disrupting the natural habitat of the Himalayan Monal and affecting its vocal communication. This study examines the impact of noise on the vocal frequency characteristics of this species across two distinct habitats, one exposed to anthropogenic noise and the other relatively undisturbed. Call parameters and noise variables were analyzed through quantile regression to understand how vocal behavior is influenced in different acoustic environments. The analysis considered multiple quantiles, including the 10th, 25th, 50th, 75th, and 95th percentiles, to capture the full range of variation in vocalization patterns. Our study is based on two hypotheses, the first hypothesis proposes that noise influences call frequency, resulting in an increase in call frequency as a response to noise. The second hypothesis suggests that call duration, particularly at the upper 90 % quantiles, exhibits varying responses to noise across different habitats, with longer calls occurring in noisier environments at higher quantiles. The results indicate that at the 10th, 50th, 75th, and 95th quantiles of call peak frequency, the pseudo-R squared values increased to 0.231, 0.215, 0.454, and 0.734, respectively, suggesting an improvement in model fit at higher quantiles. At the 95th quantile, the model accounted for approximately 73.4 % of the variation in peak frequency, whereas lower quantiles, such as the 10th and 50th percentiles, exhibited lower explanatory power. The Mean Absolute Error increased with rising quantiles, from 142.14 at q= 0.1–185.49 at q= 0.95, indicating greater variability in peak frequency at higher quantiles. This trend suggests that noise and vocal characteristics exert a more pronounced influence on the upper range of the vocal distribution, particularly at higher call frequencies, compared to lower frequencies. Additionally, a slight difference in call length was observed.