Acoustic adaptation to city noise through vocal learning by a songbird

Abstract

Anthropogenic noise imposes novel selection pressures, especially on species that communicate acoustically. Many animals—including insects, frogs, whales and birds—produce sounds at higher frequencies in areas with low-frequency noise pollution. Although there is support for animals changing their vocalizations in real time in response to noise (i.e. immediate flexibility), other evolutionary mechanisms for animals that learn their vocalizations remain largely unexplored. We hypothesize that cultural selection for signal structures less masked by noise is a mechanism of acoustic adaptation to anthropogenic noise. We test this hypothesis by presenting nestling white-crowned sparrows (Zonotrichia leucophyrs) with less-masked (higher-frequency) and more-masked (lower-frequency) tutor songs either during playback of anthropogenic noise (noise-tutored treatment) or at a different time from noise playback (control treatment). As predicted, we find that noise-tutored males learn less-masked songs significantly more often, whereas control males show no copying preference, providing strong experimental support for cultural selection in response to anthropogenic noise. Further, noise-tutored males reproduce songs at higher frequencies than their tutor, indicating a distinct mechanism to increase signal transmission in a noisy environment. Notably, noise-tutored males achieve lower performance songs than their tutors, suggesting potential costs in a sexual selection framework.

Why does noise reduce response to alarm calls? Experimental assessment of masking, distraction and greater vigilance in wild birds

“…However, most studies investigating impacts of noise have considered bird song or other signals used to attract mates and defend space (Aubin & Jouventin, ; Brumm, ; Brumm & Slabbekoorn, ; Read, Jones, & Radford, ; Shannon et al, ). Signallers may change their singing behaviour—for instance, the time of day that they vocalize and acoustic characteristics of songs—as a consequence of noise, and receiver responses to song can be compromised in noisy conditions (Brumm & Zollinger, ; Halfwerk et al, ; Moseley et al, ; Read et al, ; Slabbekoorn & den Boer‐Visser, ). Far less work has considered how noise affects other types of acoustic communication, including anti‐predator signalling (Kern & Radford, ; Lowry, Lill, & Wong, ; Morris‐Drake et al, ; Potvin, Mulder, & Parris, ).…”

Urban birdsongs: higher minimum song frequency of an urban colonist persists in a common garden experiment

“…The importance of peer interactions is consistent with a previous experiment that showed that when young dark-eyed juncos are reared together without adult tutors they are stimulated to create novel sounds (cultural innovation), copy them from each other, and modify them (cultural improvisation) into a species-typical song [65]. This type of cultural mutation would likely be biased towards higher frequencies if it occurred in a noisy urban environment [19, 21], but our common garden environment was quiet, and, therefore, the direction of this type of cultural mutation should be random or even biased towards low frequencies. Accordingly, we found that juncos from both populations in the common garden sang at significantly lower minimum frequencies than field recordings from their natal populations.…”

“…cultural mutation] in a non-random, adaptive way [19]. For example, white-crowned sparrows in noisy environments were shown to preferentially learn higher frequency songs and also to elevate the frequency of the learned songs above those of their tutor [21]. A similar combination of cultural selection and cultural mutation has been inferred for urban dark-eyed juncos based on population comparisons of song type meme pools [19].…”

“…Evidence suggests that some species preferentially learn songs that are less degraded by environmental transmission [36, 37; but see 19]. Notably, a recent study in white-crowned sparrows found that males developing in an environment with low-frequency noise preferentially learned higher frequency (less masked) songs [21]. Collectively, these results indicate that ontogenetic effects of experiencing noise during early life may affect song frequency in adulthood by the preferential learning of certain songs (i.e.…”

“…In this case, the likely selective pressure is the masking of low-frequency songs by anthropogenic noise, making those songs less adaptive (e.g. less effective signals for territoriality and mate attraction) [21]. As a result, individuals with cognitive, morphological, or sensory phenotypes that cause them to learn and/or produce higher frequency songs will have higher fitness leading to directional selection [38].…”