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.
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.
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.