Natural and anthropogenic noise increase vigilance and decrease foraging behaviors in song sparrows

Animals glean information about risk from their habitat. The acoustic
environment is one such source of information, and is an important, yet
understudied ecological axis. Although anthropogenic noise has become
recently ubiquitous, risk mitigation behaviors have likely been shaped by
natural noise over millennia. Listening animals have been shown to
increase vigilance and decrease foraging in both natural and anthropogenic
noise. However, direct comparisons could be informative to conservation
and understanding evolutionary drivers of behavior in noise. Here, we used
27 song sparrows (Melospiza melodia) and 148 laboratory behavioral trials
to assess foraging and vigilance behavior in both anthropogenic and
natural noise sources. Using 5 acoustic environments (playbacks of roadway
traffic, a white-water river, a white-water river shifted upwards in
frequency, a river with the amplitude modulation of roadway traffic, and
an ambient control), we attempt to parse out the acoustic characteristics
that make a foraging habitat risky. We found that sparrows increased
vigilance or decreased foraging in 4 of 6 behaviors when foraging in
higher sound levels regardless of the noise source or variation in
frequency and amplitude modulation. These responses may help explain
previously-reported declines in abundance of song sparrows exposed to
playback of intense river noise. Our results imply that natural
soundscapes have likely shaped behavior long before anthropogenic noise,
and that high sound levels negatively affect the foraging-vigilance
trade-off in most intense acoustic environments. Given the ever-increasing
footprint of noise pollution, these results imply potential negative
consequences for bird populations.