Ribbit and Racket: The Effects of Anthropogenic Noise on Anuran Calling Behavior in the Chicago Region
thesisposted on 01.08.2020, 00:00 by Nolan K Bielinski
Anthropogenic noise represents a major obstacle to anurans in urban landscapes because they rely heavily on vocalizations to find breeding grounds, choose mates, and settle territorial disputes. A large proportion of urban frogs may be affected by noise, as past research suggests that road-side wetlands are a major contribution to frog biodiversity and migration ability in developed landscapes. Thus, there is a need for improved monitoring and research techniques for studying anurans in urban habitats so we can better understand and mitigate the effects of noise on the ecology, behavior, and physiology of frogs. My dissertation uses soundscape methods to achieve the following: (Chapter 1) Improve how automated data collection is used in urban frog call surveys. (Chapter 2) Conduct population-level noise playback experiments to investigate how patterns in call attributes change across species, genera, and natural history characteristics. (Chapter 3) Compare results for individual-level versus population-level noise playback experiments. For my public defense, I will discuss the community-level playback study (Chapter 2). I conducted a total of 155 playback experiments on nine anuran species across 32 breeding sites around the greater Chicago region. I investigated whether patterns in call attributes (call rate, dominant frequency, call length, and pulse rate) follow taxonomic or natural history characteristics. I also tested whether the anthropogenic noise source (cars, airplanes, or trains), or the magnitude of noise level (peaks of 70, 80, or 90 dB) affected behavioral responses. I detected multivariate clustering by genus and species but not by natural history characteristics. I found notable consistency in the changes to call rate, as eight species reduced their call rate. This type of consistency has not been detected across species from past publications. The only species not to reduce call rate was also the only one to increase dominant frequency, suggesting that these are two mutually exclusive strategies for dealing with anthropogenic noise. I did not detect major patterns in call length or pulse rate changes. I also did not see consistent changes between the different noise sources, indicating that our populations were unable to perceive differences in anthropogenic noise sources and act differently as a response. For noise magnitude, most behavioral changes occurred in the 90 and 80 dB treatments, indicating that noise may only be affecting calling behavior in the loudest habitats, such as roadside ditches and retention ponds. Considering that artificial ponds contribute considerably to the biodiversity and dispersal ability of frogs in urban landscapes, noise pollution should be a concern for conservationists.