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

Abstract

Some birds in noisy areas produce songs with higher frequency and/or amplitude and altered timing compared to individuals in quiet areas. These changes may function to increase the efficacy of acoustic signals by reducing masking by noise. We collected audio recordings of redwinged blackbirds and measured noise levels. We found that males in noisier places produced songs with fewer syllables and slower repeat rate of elements in some components (rattles). Birds may also improve the efficacy of communication in noise by increasing usage of other signaling modalities. Red-winged blackbirds also perform a visual display in different intensities while singing. We also tested whether this species performs the visual display in different intensities according to current noise levels, and predicted that if the efficacy of songs is impaired in noisy places, males would compensate by performing a more intense visual display. For this, we also collected visual recordings from the same males from which we obtained acoustic recordings. We found no association between acoustic noise and the intensity of the visual display; thus, our results do not support the idea that males are using the visual display as a backup signal to communicate under acoustic noise. We discuss some possible explanations of this negative finding and for the observed noise-related changes in song length and rattle rate in the context of communication under noise.

Aircraft events correspond with vocal behavior in a passerine

“…Rather, aircraft events may stimulate increased song rate within individuals. Future research investigating if noise-exposed wood thrush also alter the pitch of their song, as has been found in urban great tits 38 , and/or the complexity of their song, as has been found in red-winged blackbirds exposed to experimental noise 39 , would be of great value. Based on our data set, the timescale at which altered vocal behavior may persist in wood thrush is also unclear.…”

Black-capped chickadees (Poecile atricapillus) alter alarm call duration and peak frequency in response to traffic noise

“…Many studies, but not all [ 22 , 41 , 46 ], report that birds lengthen their vocalizations in noisy environments. For example, Hill et al [ 47 ] reported that Oriental Magpie-Robins ( Copsychus saularis ) in urban areas sang longer songs and Walters et al [ 21 ] showed that Northern Mockingbirds ( Mimus polyglottos ) sang songs with more syllables in unmasked frequency regions in urban areas.…”

Are signals of aggressive intent less honest in urban habitats?

“…Although the acoustic response of songbirds to the noise in urban habitats has been the subject of considerable amount of research, whether acoustic noise leads to multi-modal shifts to other channels is less studied. In the most direct test of this hypothesis with songbirds, red-winged blackbirds showed no evidence that they switch to visual displays from acoustic signals under noise conditions (Ríos-Chelén et al, 2015). Given the present results, which only provide qualified support for a multi-modal shift, it is still an open question whether multi-modal shifts in response to acoustic noise occur regularly in songbirds.…”

“…While acoustic noise should affect singing behaviours, visual signals of aggressive intent should be unaffected. Indeed, males might compensate for increased acoustic noise by switching to a different modality, namely visual (Grafe et al, 2012; Partan, 2017; Patricelli & Blickley, 2006; Ríos-Chelén, Lee, & Patricelli, 2015). Under this hypothesis, urban song sparrows should switch to using wing waves to signal aggression rather than singing soft songs.…”