Songbirds use the dawn chorus to defend territories, and attract mates, but with increased urbanization the quality of communication in the dawn chorus can be negatively affected by anthropogenic noise pollution, particularly that of airplanes through masking. Avian populations may counteract these negative effects by adjusting the timing or frequency of their song, even though these adjustments could have a negative effect on fitness. To determine the threshold that noise affects the dawn chorus, we employed automatic recording units at four sites near airports along a noise gradient, from rural to increasingly urban: the Bar Ten Ranch airstrip in Arizona, the Cedar City, Saint George, and Salt Lake City airports in Utah, USA. At each site we monitored a control and a treatment area in the same habitat; the control areas were further away from the airports than the treatment sites. We are using Raven Software to measure the timing of the dawn chorus and the general noise levels in each of these sites.
Results/Conclusions
Preliminary analyses of a single ten-minute period at each site indicate that noise levels vary a lot among these sites, and some of this noise is not anthropogenic. For example, we predicted that the noise gradient would match the size and distance to the airport, yet the Max Amplitude values indicated that the site that experienced the loudest noise was the St. George Airport treatment site (32767 U), followed by the Arizona Bar Ten Ranch Treatment (29920 U), the Arizona Bar Ten Ranch Control (12388 U), the Salt Lake Airport Treatment (4155 U), the Cedar City Airport Control (1634 U), the Cedar City Airport Control (1418 U), and the Salt Lake City Airport Control (1304 U). These values are indicative of differences in wind, which will also affect sound transmission. Therefore we will use this rich data set to not only test our hypotheses about airports, but also to look at daily and seasonal rhythms of natural noise and noise pollution and see how birds respond to them.