Date of Award


Document Type


Degree Name

Master of Science


College of Arts and Sciences


Biology MS

First Advisor

James L. Hayward

Second Advisor

Shandelle M. Henson

Third Advisor

Daniel Gonzalez-Socoloske


Egg cannibalism plays a major role in the life histories of Glaucous-winged Gulls (Larus glaucescens) breeding at Protection Island, Washington. Gulls, along with other birds, visualize reflected ultraviolet (UV) light and I wondered if reflected UV light plays a role in determining which eggs are selected for cannibalization. Motivated by studies showing that tree-nesting bird eggs coated with a UV-blocking agent were less subject to predation than control eggs, I tested whether ground-nesting Glaucous-winged Gulls would preferentially predate control chicken eggs over those coated with a UV-blocking agent. Early during five mornings I formed artificial nests at randomly-determined locations in the Protection Island colony. One UV-blocked or one non-UV-blocked egg was placed in each nest. Nests were checked at 2-hour intervals. Poisson regression showed that, contrary to expectation, UV-blocked eggs were taken earlier than control eggs (p = 0.0659). This effect disappeared on days with rain (p = 0.288–0.289); however, this effect was more pronounced on days without rain (p = 0.0312). Moreover, eggs of both types survived less time during progressively later days (p < 0.001).

Subject Area

Glaucous-winged gull--Behavior, Glaucous-winged gull--Cannibalism, Eggs, Protection Island National Wildlife Refuge (Wash.)

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