Date of Award

8-2019

Degree Name

Doctor of Philosophy

Department

Biological Sciences

First Advisor

Dr. Sharon A. Gill

Second Advisor

Dr. Maarten Vonhof

Third Advisor

Dr. Steven L. Kohler

Fourth Advisor

Dr. Kathleen M. Baker

Keywords

Anthropogenic noise, Avian signaling behavior, social factions

Abstract

Rapid human-generated environmental change has irrevocably altered the natural world. Understanding how animal populations respond and persist within these modified landscapes is critical for mitigating associated negative environmental impacts. For organisms that rely on vocal communication, anthropogenic noise masks signals, reducing the area over which vocalizations can be heard. For birds, noise overlaps with songs males use to defend breeding areas and attract mates, both critical aspects of reproduction. In response to noise, males adjust their song structure, but whether they actually benefit from song changes is unknown. Moreover, it remains unclear whether noise disrupts communication by affecting interactions with mates, neighbors, or intruder detection.

I tested the hypothesis that anthropogenic noise affects multiple components of communication systems, including signalers, their signals, and receivers. I studied male house wrens (Troglodytes aedon), asking first whether noise influences song structure, and then considering whether noise alters transmission of songs through space, and perception of singing during territorial intrusions as well as within social networks. In Chapter 1, I show that paired males adjusted their song frequency in response to noise playback, whereas unpaired males do not. Unpaired males may not change their songs if they are constrained by female preferences for low-frequency song. In Chapter 2, I show individuals plastically adjusted some but not all song traits in response to variation in immediate noise levels, and that social context and ambient noise affected song structure across males. In Chapter 3, I show song amplitude fell below thresholds for detection and discrimination within a male’s own territory under high noise conditions, suggesting that noise masking may affect house wren spatial ecology. Because noise decreases signal active space, masking may compromise the ability of males to detect and respond to intruders. In Chapter 4, noise did not influence detection of simulated territorial intruders, but did affect aggression by territorial males. Males attacked speakers broadcasting intruder song more under noisy than quiet conditions, suggesting they may be unable to assess intruders based on songs alone and rely on close encounters for discrimination. In Chapter 5, I show that although noise affected male responses to territorial intruders, social context predicted singing by neighboring males. Social networks may be resilient to short-term changes in singing by any one male and change in patterns of vocal interactions may occur over longer periods of time. My research demonstrates that noise affects each part of the communication system, beginning with the songs males produce, to their transmission, and reception by receivers. However, social factors sometimes had larger impacts on singing as they modified male responses to noise, indicating a complex interaction among factors that influence song. Thus, noise masking could act as an important selective pressure on animal signals, but its effects depend on the social context in which signal are given. My research advances our understanding of how both noise and social context affect communication, all of which may have implications for individual fitness, population dynamics, and ultimately the persistence of populations in urban environments.

Access Setting

Dissertation-Open Access

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