Date of Award

Spring 1-1-2010

Document Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Ecology & Evolutionary Biology

First Advisor

Alexander Cruz

Second Advisor

Sharon Collinge

Third Advisor

Robert Guralnick

Abstract

Human-generated noise pollution has emerged swiftly on a global scale and it presents an evolutionarily novel condition for species that rely on acoustic communication, especially birds. Noise may mask or interfere with bird communication, limiting bird distributions or resulting in lowered reproductive success. However, studies have not definitively linked bird declines to noise because other mechanisms could explain declines, such as confounding noise exposure with edge habitat, vehicular motion and lights, and mortality from bird-vehicle collisions.

My study design provided a "natural experiment" that eliminated the influence of confounding factors common to noisy habitats and isolated noise as a single experimental variable to determine whether noise negatively influences birds via acoustic masking and to explore the consequences of noise exposure on ecological communities. I found that noise reduces nesting species richness and alters community composition. Species-specific tolerances to noise appear to be explained by vocalization frequency: species that avoid noisy habitat have low frequency vocalizations, and are larger bodied, and those tolerant of noise are smaller and have higher pitched vocalizations that escape acoustic masking by low-frequency noise. Despite this general trend, some, but not all, species adjust vocal signals in response to noise, which may permit them to be heard in noisy habitats. In terms of nesting success, and contrary to expectations, birds nesting in noisy areas benefit from increased reproductive success due to less nest predation. This pattern was observed for real nests and confirmed with artificial nest experiments. Finally, through landscape-level modeling efforts, I demonstrate that noise can be effectively managed to minimize the influence of this novel disturbance on natural communities.

These findings have broad implications for noisy habitats around the world: (i) if higher nest success is widespread in noisy environments, it may help explain the general success of many synanthropic species and the homogenization of urban avian communities, (ii) acoustics can structure avian communities, though nonrandomly, (iii) noise may have unexpected indirect effects on ecological communities due to species-specific responses to noise by species with important ecological roles, but (iv) mitigation efforts can successfully reduce the influence of noise on wildlife.

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