Low-frequency songs lose their potency in noisy urban conditions

Abstract

Many animal species communicate with their mates through acoustic signals, but this communication seems to become a struggle in urbanized areas because of increasing anthropogenic noise levels. Several bird species have been reported to increase song frequency by which they reduce the masking impact of spectrally overlapping noise. However, it remains unclear whether such behavioral flexibility provides a sufficient solution to noisy urban conditions or whether there are hidden costs. Species may rely on low frequencies to attract and impress females, and the use of high frequencies may, therefore, come at the cost of reduced attractiveness. We studied the potential tradeoff between signal strength and signal detection in a successful urban bird species, the great tit (Parus major). We show that the use of low-frequency songs by males is related to female fertility as well as sexual fidelity. We experimentally show that urban noise conditions impair male-female communication and that signal efficiency depends on song frequency in the presence of noise. Our data reveal a response advantage for high-frequency songs during sexual signaling in noisy conditions, whereas low-frequency songs are likely to be preferred. These data are critical for our understanding of the impact of anthropogenic noise on wild-ranging birds, because they provide evidence for low-frequency songs being linked to reproductive success and to be affected by noise-dependent signal efficiency. signal evolution | noise pollution | frequency-dependent masking | extra-pair paternity | signal trade-off

Anthropogenic noise weakens territorial response to intruder's songs

“…Results from laboratory-based behavioral studies of great tits (Parus major) show that noisy conditions increase the detection threshold of biologically relevant frequencies by up to 18 dB and that urban noise favors detection of highfrequency songs (Pohl et al 2009(Pohl et al , 2012. Other experiments in great tits have shown that lowfrequency songs, which are most easily masked by noise pollution, are preferred by females and linked to reproductive success, and that female response latency to male songs within noise leads to alteration of male behavior (Halfwerk et al 2011(Halfwerk et al , 2012. Experiments with European robins (Erithacus rubecula) show that vocal responses to playbacks of conspecific songs paired with simulated traffic noise might change in complexity and pitch (McMullen et al 2014).…”

Reply to Eens et al.: Urban noise can alter sexual selection on bird song

“…We performed an adequate test on 22 male great tits and found cuckolded males to sing higher-frequency songs compared with noncuckolded males (2). Furthermore, although we could not assign the genetic fathers for all chicks in our study, we do not think it is premature to conclude that reproductive success is related to spectral performance, as it is unlikely that the loss of own-pair paternity is compensated by a gain in extrapair paternity.…”

“…Our data further suggest that the time window to escape mate guarding before sunrise is very small and possibly constrained by egg-laying itself. Females do not leave their nest box as early when they have started laying eggs (2). It is also known that eggs can be fertilized by sperm stored before laying (3) and that extrapair chicks are mainly found in the first-laid eggs (3,4).…”

Multimodal cues improve prey localization under complex environmental conditions

“…The underlying perceptual mechanism that may increase detection and/or localization when using multimodal cues under increased levels of environmental complexity, however, is still unclear [12]. For instance, acoustic noise can mask acoustic signals when overlapping in frequency [18][19][20]; adding visual signal components to a sexual display may reduce this masking impact [21]. Acoustic noise can also provide extra sensory information that, though irrelevant, nevertheless must be processed by an animal's brain [12].…”