Immediate spectral flexibility in singing chiffchaffs during experimental exposure to highway noise

Abstract

SUMMARYSound plays an important role in the life of many animals, including many bird species. Typically, male birds sing to defend a territory and to attract mates. Ambient noise may negatively affect the signal efficiency of their songs, which may be critical to reproductive success. Consequently, anthropogenic noise may be detrimental to individual birds and to populations in cities and along highways. Several bird species that are still common in urban areas have been shown to sing at higher frequency at locations where there is more low-frequency traffic noise. Here we show that chiffchaffs along noisy highways also sing with a higher minimum frequency than chiffchaffs nearby at a quiet riverside. Furthermore, through experimental exposure to highway noise we show that these birds are capable of making such adjustments over a very short time scale. The first 10 songs sung during the noise exposure revealed an immediate shift to higher frequencies, with a return to pre-exposure levels in recordings without noise the following day. In a transmission re-recording experiment we tested the impact of a potential measurement artifact by recording playback of the same songs repeatedly under different controlled noise conditions. We found an upward shift in the minimum frequency measurement associated with more noisy recordings of the same song, but this artifact was not of a scale that it could explain the noise-dependent spectral shifts in chiffchaffs.

Anthropogenic noise affects song structure in red-winged blackbirds (Agelaius phoeniceus)

“…The volume on the loudspeaker was set so that the amplitude of the experimental stimulus measured 89dBC (C-weighted decibels) SPL (sound pressure level) at a distance of 1m (measured with a RadioShack sound level meter, model 33-4050, slow response; Fort Worth, TX, USA). This amplitude is comparable to that used in another study [86dBA SPL at a distance of 1m (Verzijden et al, 2010)] and is typical of general highway traffic (mean ± s.d., 72±18dBA SPL at roadside, with 25% of all measurements >88dBA SPL) (Lengagne, 2008) and heavy commercial truck traffic (10-90% range, 76-86dBA SPL at a distance of 7.5m) (Stephenson and Vulkan, 1968).…”

“…Many species improve signal detectability by increasing the minimum frequency of their songs, which, because of the low-frequency nature of anthropogenic noise, can reduce masking effects (e.g. Bermúdez-Cuamatzin et al, 2009;Kirschel et al, 2009;Ripmeester et al, 2010;Verzijden et al, 2010). In our study, the minimum frequency of trills did not differ between treatments, perhaps because the frequency range of red-winged blackbird trills (2.75-5.0kHz) exceeded the frequencies contained in our experimental low-frequency white noise (0-1.83kHz) and exceeded the majority of frequencies produced by traffic (again, traffic noise is concentrated below 3kHz) (Cornillon and Keane, 1977;Halfwerk et al, 2010;Wood and Yezerinac, 2006).…”

“…A concern in the transient noise experiment was that the broadcasted low-frequency white noise could have directly affected the measurements of song structure (Verzijden et al, 2010). This seems unlikely, however, as our 2kHz high-pass filter should have completely removed the low-frequency white noise without affecting trill structure.…”

“…This seems unlikely, however, as our 2kHz high-pass filter should have completely removed the low-frequency white noise without affecting trill structure. Nevertheless, we conducted a validation procedure similar to that used by Verzijden and colleagues (Verzijden et al, 2010) to ensure that our measurements were not affected directly by the experimental treatment. To achieve this, we replicated our transient anthropogenic noise experiment but, instead of recording live subjects, we recorded simulated subjects that could not have changed the structure of their songs between the two experimental treatments.…”

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

“…Because most energy of urban noise is found at low frequencies, an increase in song frequencies may reduce noise masking. These changes may arise during ontogeny due to selective learning of the songs most easily heard (Luther and Baptista 2009;Ríos-Chelén et al 2012), and/or these changes may reflect behavioral plasticity, with birds changing their songs in Breal-time^while experiencing different noise levels (Tumer and Brainard 2007;Halfwerk and Slabbekoorn 2009;Gross et al 2010;Verzijden et al 2010;Bermúdez-Cuamatzin et al 2011). These changes in vocalizations may also arise through evolutionary divergence among populations, though there is little evidence of genetic differences between populations in noisy and quiet areas (Partecke et al 2004(Partecke et al , 2006; but see Partecke and Gwinner 2007).…”