Anthropogenic noise and noise-adjusted signals influence territorial-defense behaviors of male Baird’s sparrows (Centronyx bairdii)
Anthropogenic noise can constrain the acoustic communication of wildlife species through acoustic masking. However, many species display noise-adjusted signals which are theorized to provide release from acoustic masking. Yet, noise-adjusted signals may alter how receivers perceive and respond to signalers or fail to improve acoustic detection under noisy conditions. Thus, noise and noise-adjusted signals could have consequences for species that rely on acoustic communication for breeding. Baird’s sparrow (Centronyx bairdii) is a grassland bird species that displays noise-adjusted songs. To investigate the potential impacts of noise and noise-adjusted songs on the intrasexual behavior of this species, I conducted repeated measures playback studies (n = 69 dyads) on free-living male Baird’s sparrows. My research took place in the mixed-grass prairies of Southern Alberta during the species breeding season (May to July 2018 and 2019). To simulate territory intrusions in ‘noisy’ and ‘quiet’ conditions, I used a playback design to broadcast unadjusted and noise-adjusted Baird’s sparrow song and oil-well drilling noise to individual male birds. To determine if song or noise treatment influenced male behavior, I compared the number of songs, calls, flybys over the experimental speaker, and song latency for each trial type. Focal male song latency was longer for unadjusted songs broadcast with noise versus without noise, suggesting that noise constrained acoustic detection. However, song latency for noise-adjusted songs broadcast with noise was similar to unadjusted songs broadcast in quiet conditions, suggesting that noise-adjusted songs are easier to detect acoustically in noise. I concluded that noise-adjusted songs partially restore acoustic communication in noisy conditions. The remaining focal male responses did not differ significantly by song treatment, suggesting that the song types are functionally equivalent. However, responses differed significantly between noise treatments. Focal males sang fewer songs whilst increasing alarm call vocalizations and engaged in more flybys under noisy conditions. These results suggest that noise heightens aggression in individuals or that males use different strategies to determine the location and fighting ability of rivals in the presence of noise. While it is uncertain what mechanism(s) underly these behavioral changes, I concluded that anthropogenic noise acts as a disturbance to this species.
Animal behavior, Conservation behavior, Anthropogenic noise