Urban sparrows respond to a sexually selected trait with increased aggression in noise

Abstract

Animals modify acoustic communication signals in response to noise pollution, but consequences of these modifications are unknown. Vocalizations that transmit best in noise may not be those that best signal male quality, leading to potential conflict between selection pressures. For example, slow paced, narrow bandwidth songs transmit better in noise but are less effective in mate choice and competition than fast paced, wide bandwidth songs. We test the hypothesis that noise affects response to song pace and bandwidth in the context of competition using white-crowned sparrows (Zonotrichia leucophrys). We measure male response to song variation along a gradient of ambient noise levels in San Francisco, CA. We find that males discriminate between wide and narrow bandwidth songs but not between slow and fast paced songs. These findings are biologically relevant because songs in noisy areas tend to have narrow bandwidths. Therefore, this song phenotype potentially increases transmission distance in noise, but elicits weaker responses from competitors. Further, we find that males respond more strongly to stimuli in noisier conditions, supporting the ‘urban anger’ hypothesis. We suggest that noise affects male responsiveness to song, possibly leading to more territorial conflict in urban areas.

Aircraft sound exposure leads to song frequency decline and elevated aggression in wild chiffchaffs

“…Chiffchaffs exposed to aircraft noise responded more aggressively to simulated territorial intrusions than control birds, similar to other species exposed to anthropogenic noise (Phillips & Derryberry, ). In general, urban birds tend to be more aggressive, but whether this is due to noise or other urban factors is not clear (Davies & Sewall, ).…”

Surviving in the city: higher apparent survival for urban birds but worse condition on noisy territories

“…). Animals may also have to change their territorial behaviors in noisy urban conditions, such as approaching more closely to be able to hear an acoustic signal, which could lead to aggressive territorial interactions and potentially affect body condition, reproduction, and survival (Phillips and Derryberry ).…”

“…Nestlings raised in noisy conditions are exposed to increased stressors and have decreased body condition, which may have cascading effects into future reproductive success (Crino et al 2013, Salm on et al 2016, Raap et al 2017. Animals may also have to change their territorial behaviors in noisy urban conditions, such as approaching more closely to be able to hear an acoustic signal, which could lead to aggressive territorial interactions and potentially affect body condition, reproduction, and survival (Phillips and Derryberry 2018).…”

Cities as evolutionary experiments

“…Other examples, such as song sparrows in North America, have also been found [4]. Sparrows have also been found to become more territorial and aggressive in noisy city settings [5].…”