![]() ![]() 2008 Fregatidae: Juola and Searcy 2011 Cricetidae: Pasch et al. One physical challenge in the production of acoustic signals is a trade-off between the rate at which sounds are produced and the frequency bandwidth of those sounds (Parulidae: Cardoso and Hu 2011 Dendrocolaptinae: Derryberry et al. 1992 Gil and Gahr 2002 Podos and Nowicki 2004 ). For many taxa, the ability of the signaler to produce physically challenging signals may also be an indicator of condition ( Nowicki et al. 2002 ) may reflect nutritional condition during formation of the trait (e.g., molt or song learning, respectively). For example, the brightness of carotenoid-based plumage ( Hill and Montgomerie 1994 ) or the production of larger and more complex song repertoires ( Nowicki et al. Signals for mate attraction and territory defense often contain important information about the condition of the signaler. The fitness costs and benefits to signalers and receivers of these modified signals are just beginning to be explored ( Slabbekoorn 2013 ). A response in many different taxa has been an increase in the minimum frequency of acoustic signals, which should increase signal transmission and detectability by reducing overlap with low-frequency anthropogenic noise (reviewed in Slabbekoorn 2013 ). 2007 Nemeth and Brumm 2009 Parris and Schneider 2009 Francis et al. Animals with acoustic signals used for long-distance communication, which are often used for territory defense and mate attraction, are susceptible to interference from anthropogenic noise ( Slabbekoorn and Peet 2003 Patricelli and Blickley 2006 Nowacek et al. There is increasing evidence that this noise is affecting the behavior and potentially fitness of wild animal populations ( Slabbekoorn and Peet 2003 Francis et al. Ultimately, the lower vocal performance of birds on territories with high levels of anthropogenic noise could result in fewer mating opportunities and more challenges in defending their territory.Īnthropogenic noise is part of most modern environments ( Barber et al. Our results therefore suggest that reduced bandwidth and performance-not higher minimum frequency-could be the reason that urban birds are less responsive to songs adjusted for anthropogenic noise. Males responded more strongly to normal than to reduced bandwidth songs, but equally to high- and low-pass filtered songs. We conducted playback experiments to test if lower responses to urban songs are due to higher minimum frequencies or to narrower bandwidths. These results suggest that behavioral adjustments to anthropogenic noise reduce vocal performance of songs. Males on louder territories produced songs at higher minimum frequencies but also with reduced bandwidth and lower vocal performance. We investigated the relationship between anthropogenic noise amplitude and male white-crowned sparrow vocal performance in San Francisco, CA. This measure of vocal performance is a trait under sexual selection in many taxa. There is a performance challenge to producing notes rapidly at a wide bandwidth, and any reduction in bandwidth necessarily reduces the performance value. ![]() Lower response may be due to higher minimum frequencies or to the associated decrease in frequency bandwidth. In many taxa, minimum frequencies of acoustic signals increase with ambient noise levels, and males and females respond less strongly to these adjusted signals. Anthropogenic noise affects the behavior of a variety of animal taxa around the world. ![]()
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