Presentation Title

P-25 Experiments on the Effect of UV Reflectance on Egg Predation by Gulls

Presenter Status

Professor Emeritus of Biology

Second Presenter Status

Professor of Mathematics and Ecology

Third Presenter Status

Department of Biology

Fourth Presenter Status

Department of Biology

Preferred Session

Poster Session

Start Date

3-11-2017 2:00 PM

End Date

3-11-2017 3:00 PM

Presentation Abstract

Conspecific egg predation (egg cannibalism) is common in gull colonies. Studies by our Seabird Ecology Team demonstrated that the rate of egg cannibalism by Glaucous-winged Gulls increases when food supplies are scarce, such as during El Niño-Southern Oscillation (ENSO) events. Gull retinas are sensitive to UV light reflectance. We hypothesized that UV light reflectance influences the selection of eggs by gulls for predation. We performed four experiments, each of which involved placing 50 white chicken eggs in randomly-placed artificial nests in the gull colony. Half the eggs were coated with a UV-blocking agent and the other half were coated with a control substance that did not block UV reflectance. The eggs were checked at 2-hour intervals throughout the day. Poisson regression showed that UV-blocked eggs were taken earlier than control eggs, although this effect disappeared on days with rain. Given that most gull eggs reflect little UV light, we concluded that gulls selectively preyed on chicken eggs that reflected light most like eggs of their own species, and that UV light reflectance plays a role in egg predation by gulls.

Acknowledgments

We thank the U.S. Fish and Wildlife Service for permission to work on Protection Island, Cape George Colony Club for permission to use their marina, and Rosario Beach Marine Laboratory for logistical support. Financial support for this project was provided by Andrews University Office of Research and Creative Scholarship and U.S National Science Foundation Grant DMS-1407040.

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Nov 3rd, 2:00 PM Nov 3rd, 3:00 PM

P-25 Experiments on the Effect of UV Reflectance on Egg Predation by Gulls

Conspecific egg predation (egg cannibalism) is common in gull colonies. Studies by our Seabird Ecology Team demonstrated that the rate of egg cannibalism by Glaucous-winged Gulls increases when food supplies are scarce, such as during El Niño-Southern Oscillation (ENSO) events. Gull retinas are sensitive to UV light reflectance. We hypothesized that UV light reflectance influences the selection of eggs by gulls for predation. We performed four experiments, each of which involved placing 50 white chicken eggs in randomly-placed artificial nests in the gull colony. Half the eggs were coated with a UV-blocking agent and the other half were coated with a control substance that did not block UV reflectance. The eggs were checked at 2-hour intervals throughout the day. Poisson regression showed that UV-blocked eggs were taken earlier than control eggs, although this effect disappeared on days with rain. Given that most gull eggs reflect little UV light, we concluded that gulls selectively preyed on chicken eggs that reflected light most like eggs of their own species, and that UV light reflectance plays a role in egg predation by gulls.