Vocal Response to Traffic Noise in a Non-Passerine Bird: The Little Bustard Tetrax tetrax

Abstract

Anthropogenic noise is spreading worldwide and can interfere with the acoustic communication of multiple animal groups. Species communicating in low-frequency ranges (having large sound production structures) and with limited vocal learning are expected to be especially vulnerable to human noise-induced masking interference. Yet how such species may confront this emerging impact has scarcely been explored. Here we examined the effect of anthropogenic noise on the calling behaviour of a sizeable non-passerine bird, the Little Bustard Tetrax tetrax, across a gradient of road traffic noise and in relation to male position within the lek. Using directional recordings and noise mapping, we determined inter– and intra-individual variation in call parameters and their relationship with noise level and frequency at both spatial and temporal scales, defined respectively as (i) variation of noise according to the position of the calling sites of each male within the lek (spatial scale) and (ii) fine temporal variation of noise experienced by individual males immediately prior to each call (temporal scale). Little Bustard males increased their call rate at sites exposed to higher average noise levels and at those located further from the nearest neighbour within the lek, whereas temporal changes in noise showed no effect on call rate. In contrast, call duration decreased with relative increases in noise level prior to each call, being unaffected by spatial changes in noise. Peak call frequency showed no significant variation over time and among sites. Our findings reveal that, despite its supposedly limited vocal learning, this species seems to exhibit fine-scale vocal adjustment, which implies some capacity to cope with anthropogenic noise. However, the lack of frequency shift suggests behavioural constraints that may compromise communication as the species uses low-pitched calls. This study provides insights into how some non-passerine birds may adjust their vocal sexual display to anthropogenic noise.—Barrero, A., Llusia, D., Traba, J., Iglesias-Merchan, C. & Morales, M.B. (2021). Vocal response to traffic noise in a non-passerine bird: the Little Bustard Tetrax tetrax. Ardeola, 68: 143-162.