Date of Award


Document Type


Degree Name

Master of Science


College of Arts and Sciences

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.)

Creative Commons License

Creative Commons Attribution-No Derivative Works 4.0 International License
This work is licensed under a Creative Commons Attribution-No Derivative Works 4.0 International License.


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