Geographically pervasive effects of urban noise on frequency and syllable rate of songs and calls in silvereyes (Zosterops lateralis)

Abstract

Recent studies in the Northern Hemisphere have shown that songbirds living in noisy urban environments sing at higher frequencies than their rural counterparts. However, several aspects of this phenomenon remain poorly understood. These include the geographical scale over which such patterns occur (most studies have compared local populations), and whether they involve phenotypic plasticity or microevolutionary change. We conducted a field study of silvereye (Zosterops lateralis) vocalizations over more than 1 million km 2 of urban and rural south-eastern Australia, and compared possible effects of urban noise on songs (which are learned) and contact calls (which are innate). Across 14 paired urban and rural populations, silvereyes consistently sang both songs and contact calls at higher frequencies in urban environments. Syllable rate (syllables per second) decreased in urban environments, consistent with the hypothesis that reflective structures degrade song and encourage longer intervals between syllables. This comprehensive study is, to our knowledge, the first to demonstrate varied adaptations of urban bird vocalizations over a vast geographical area, and to provide insight into the mechanism responsible for these changes.

Bird song and anthropogenic noise: vocal constraints may explain why birds sing higher-frequency songs in cities

“…they increase the amplitude of their vocalizations in response to an increase in background noise (reviewed in [19]), which is used to communicate in the presence of anthropogenic noise [20]. It is also often observed that birds sing at higher frequencies at noisy locations [21][22][23][24][25], which is probably the result of vocal plasticity [26][27][28].…”

Anthropogenic noise is associated with changes in acoustic but not visual signals in red-winged blackbirds

“…Ríos-Chelén et al (2012) found that the minimum frequency of learnt vocalizations (i.e., oscine songs) show a tighter adjustment (i.e., bigger effect size) with noise levels than the minimum frequency of nonlearnt vocalizations (i.e., sub-oscine songs), presumably because the scope for song variation is related to the process of song learning (Kroodsma 1982). Studies on vocal pitch adjustment to noise for one type of presumably nonlearnt vocalization, bird call, have reported different results: While there are studies showing an association between noise and call minimum frequency (Leonard and Horn 2008;Potvin et al 2011;, a recent study by Grace and Anderson (2015) found no association between the minimum frequency of Carolina chickadees (Poecile carolinensis)'s calls and noise levels. Grace and Anderson (2015) also remarked the importance of measuring minimum frequencies using power spectra (as we did in the present study), rather than from spectrograms, to avoid the possibility of measuring bias resulting from masking noise.…”

“…In some bird species, individuals in areas with higher anthropogenic noise sing songs with higher frequency (i.e., pitch), than individuals in quiet areas (e.g., Slabbekoorn and Communicated by H. Brumm Peet 2003;Fernández-Juricic et al 2005;Slabbekoorn and den Boer-Visser 2006;Wood and Yezerinac 2006;Bermúdez-Cuamatzin et al 2009;Hu and Cardoso 2009;Nemeth and Brumm 2009;Potvin et al 2011). These and other noise-related changes in acoustic signals may improve the efficacy of communication in noise (Lohr et al 2003;Halfwerk et al 2011b;Pohl et al 2012Pohl et al , 2013.…”

Is sociality required for the evolution of communicative complexity? Evidence weighed against alternative hypotheses in diverse taxonomic groups

“…The influence of the environment on the transmission of animal signals is well documented [27 -30]. Background acoustic or visual noise masks calls [31,32] and displays [33,34] and obstructions in the environment deflect and scatter sound waves [28] and obscure visual signals [35,36], as does the reduced visibility imposed by poor light [37][38][39]. The strategies animals adopt to enhance signal fidelity in noisy, cluttered or dim habitats are varied.…”