Anthropogenic noise imposes novel selection pressures on organisms, especially on species that communicate acoustically. Recent research in acoustic communication has found that animals produce different vocalizations in the presence of human generated noise compared to quieter areas. However, the mechanism for these vocal differences remains poorly understood. Here we address the question of how young birds learn songs in the face of low-frequency noise characteristic of cities. We explore how young males select songs to copy and how these selections may drive cultural evolution in a behavioral model, white-crowned sparrows (Zonotrichia leucophrys). We reared males in two groups and tutored both with two categories of songs – higher frequency songs less masked by noise, and lower frequency songs more masked by noise. Young males in the experimental group heard city-like noise masking their tutor songs whereas control males heard city-like noise at a separate time from song tutoring.
Results/Conclusions
We find that experimental males copied the less masked songs significantly more often, while control males showed no significant difference in copying, providing the first experimental evidence of cultural selection to avoid the masking effects of anthropogenic noise. Further, experimental birds reproduced songs at higher frequencies and lower vocal performance than that of their tutor songs, while control males showed no significant differences compared to their tutor songs. These results suggest how anthropogenic noise may impact cultural evolution by shifting the acoustic landscape to higher frequency songs with elements less masked by noise. However, males shifting their songs to increase signal transmission may face a tradeoff in their potential vocal performance, and thus decrease their advertisement potential. We discuss the evolutionary implications of these findings for how birds cope acoustically in urbanized environments.