Publication Date

5-2015

Date of Final Oral Examination (Defense)

1-29-2015

Type of Culminating Activity

Thesis

Degree Title

MS Raptor Biology

Department

Biology

Major Advisor

Jesse R. Barber, Ph.D.

Advisor

James Belthoff, Ph.D.

Advisor

Ian C. Robertson, Ph.D.

Abstract

Anthropogenic noise has increased dramatically worldwide which has negatively impacted wildlife. The effect of noise on acoustically specialized predators has received limited attention. Here I demonstrate that noise generated by a natural gas compressor station degrades the ability of the northern saw-whet owl (Aegolius acadius) to detect and capture prey in the absence of light. The saw-whet owl is considered an acoustic specialist because it exhibits a high degree of ear asymmetry, an adaptation for precise three-dimensional sound localization in birds. I presented 31 wild-caught saw-whet owls with mice (Mus musculus) inside a flight tent under acoustic conditions ranging from control 29 dB(A) to 73 dB(A). By varying the noise treatments in intensity and spectral composition I recreated acoustic conditions corresponding with distances between 50 - 800 m from an active compressor station. I found that saw-whet owls were able to capture prey using hearing alone but were not able to capture mice at or above 61 dB(A), i.e., noise intensities found within 200 m of a compressor station. In order to assess the manner by which noise affected owl hunting, I postulated multiple hypotheses. First, the noise levels used in this experiment might affect owl hunting by the same amount, which I labeled the threshold hypothesis. Secondly, noise impacts might increase with increasing noise, which I labeled the dose-response hypothesis. I compared these hypotheses using a model selection framework. Hunting deficits increased with increasing noise lending support to the dose-response hypothesis. Each decibel increase in noise between 29-73 dB(A) resulted in an 11% decrease in the odds of the owl orienting toward its prey during a trial, a 7% decrease in the odds of a strike, and an 8% decrease in the odds of successfully capturing the mouse. These results suggest that unmitigated natural gas compressor station noise has the potential to decrease habitat suitability for acoustically specialized owls.

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