Date of Award


Degree Name

MS in Biological Sciences


Biological Sciences


College of Science and Mathematics


Clinton Francis

Advisor Department

Biological Sciences

Advisor College

College of Science and Mathematics


Background noise is ubiquitous and can impair acoustic communication and influence signaling behavior in animals. Despite evidence demonstrating myriad effects of anthropogenic noise on animal communication, precisely how natural background noise influences communication and behavior remains unclear. Yet, natural sources of background noise, such as rushing rivers or crashing ocean surf, share similar power spectra to sources of anthropogenic noise and can occur at high amplitudes, potentially masking acoustic signals.

To investigate the effects of water-generated noise on songbird behavior, we experimentally broadcast landscape-level playbacks of ocean surf and river noise in coastal California, USA, and riparian habitat in Idaho, USA, respectively. In Chapter 1, we conducted a conspecific playback experiment examining how territorial defense behaviors of lazuli buntings (Passerina amoena) and spotted towhees (Pipilo maculatus) vary in response to broadcast water noise. We also incorporated cicada noise from a serendipitous Okanagana spp. emergence as a biotic source influencing lazuli bunting behavior. Both species produce songs that share substantial spectral overlap with low-frequency, water-generated noise, and lazuli bunting song shares an additional high-frequency overlap with cicada calls. Thus, there is potential for background acoustic conditions to mask conspecific signals. We found that detection and discrimination of conspecific playback occurred more slowly for both species as sound level increased. Lazuli buntings also exhibited divergent flight behaviors in response to high- and low-frequency acoustic sources, both dependent and independent of sound level.

In Chapter 2, we investigated how amplitude and frequency of water-generated noise influences spectral and temporal song characteristics in six songbird species. We recorded individuals defending territories across 37 sites, with each site representing one of four acoustic environments: naturally quiet ‘controls’, naturally noisy ‘positive controls’ adjacent to the ocean or a whitewater river, ‘phantom’ playback sites with continuous broadcast of low-frequency water noise, and ‘shifted’ playback sites with continuous broadcast of high-frequency water noise. We predicted that all individuals exposed to ‘positive control’, ‘phantom’, or ‘shifted’ noise would adjust song structure, but the magnitude of signal modification would be larger in noisier locations and the type of modification would depend on the spectral profile of the acoustic environment. No two species altered songs in precisely the same way. However, song structure of all six species varied with amplitude and/or frequency of background noise.

Together our results demonstrate that natural noise can impair agonistic behaviors and influence vocal structure. These findings suggest that the natural acoustic environment shapes acoustic communication, highlighting natural soundscapes as an under-appreciated axis of the environment.