Date Awarded

2021

Document Type

Thesis

Degree Name

Master of Science (M.Sc.)

Department

Biology

Advisor

John P Swaddle

Committee Member

Daniel A Cristol

Committee Member

Matthias Leu

Abstract

Bird-window collisions account for millions of bird deaths annually in the United States. Despite many correlative studies citing the potential influence of reflective glass on daytime collision risk, few studies have explicitly tested this hypothesis. We aimed to determine whether reflection from a window influences daytime collision risk by manipulating the lighting conditions on exterior and interior window surfaces. We conducted this research within a flight tunnel in which domesticated zebra finches (Taeniopygia guttata) flew towards a window structure with two windows situated behind a mist-net. We assessed collision risk and flight velocity through 3D videography. We predicted that risk of collision and flight velocity would be greater when windows were manipulated to reflect more light, regardless of exterior lighting conditions. We found no support for our predictions. In contrast, we found that collision risk decreased in the presence of a reflection during bright, midday exterior lighting conditions. Some trends lacking statistical support suggest that reflection may increase collision risk, but likely only at certain times of day. We documented a greater number of collisions and slightly increased flight velocity towards windows which reflected more light in the morning. Reflection has often been hypothesized and documented as a detrimental risk factor. We suggest that the influence of window reflection on daytime window collisions is more complex than assumed and might involve previously unaccounted properties of light such as polarization. Mitigation technology has often been tested in the absence of ecologically relevant lighting conditions which may solely influence risk of collision. We call for the implementation of more robust, standardized methods of testing which account for realistic lighting conditions which birds might experience. Altering lighting conditions throughout the day could be implemented as an additional mitigation strategy, though the influence of lighting conditions on collision risk needs to be studied on a broader scale.

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