The effects of short-term anthropogenic noise on acoustic production and perception in songbirds
Anthropogenic noise is increasing worldwide and its effects on animals are of increasing concern. Songbirds, utilize a variety of acoustic signals to facilitate behavior related to mate acquisition, territory defense, and predator avoidance. Masking by low-frequency anthropogenic noise may affect both production and perception of vocalizations, potentially resulting in reduced fitness. During vocal production some songbirds alter song pitch and amplitude to adapt to chronically noisy habitats. However, less is known about the effect of short-term noise exposure on site persistence and adjustment to rates of song production. We presented simulated traffic noise in otherwise quiet habitats for three consecutive mornings. We assessed songbird persistence after each playback session, and recorded vocal behavior during one minute gaps in playback to assess whether rates of singing were altered during noise presentation. In a second playback experiment we examined the effects of noise on perception. Specifically, we asked whether anthropogenic noise affected the ability of foraging songbirds to perceive and respond to acoustic threats. To test this, we played back calls of a predatory Cooper’s hawk at bird feeders in an urban environment. Calls were presented with and without masking anthropogenic noise, and anti-predator behaviors were monitored in foraging songbirds.
The results from noise playback experiments examining site persistence and rate of song production show that songbirds residing within noise-affected areas neither left the area, nor modified their singing behavior as a result of short-term playback. Thus, negative impacts from short-term noise exposure were not immediately evident, although measures of reproductive success are needed to assess fitness. The lack of observed behavioral flexibility suggests that many of the species encountered in our experiment may not make rapid behavioral adjustments to location or song rate that could otherwise increase their fitness in the presence of chronic noise. Somewhat surprisingly, common feeder birds in our experimental test of perception did not significantly alter their behavior in response to overlapping road noise, suggesting that they perceived predator calls equally as well. Whether this ability is common among songbird species more averse to human habitation is not known. In sum, anthropogenic noise did not alter presence, song production, or the perception of predators in a pair of field playback experiments. Comparisons between urban adapters and avoiders may clarify whether these behaviors differ between species, facilitating noise adaption within a limited group of songbirds.