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2. Ashmole N. (1971). Seabird ecology and the marine environment. Pp. 223-287 In Avian biology, vol. 1. ( D. S. Farner and J. R. King , Eds.). New York: Academic Press.
3. BirdLife International (2012) Spotlight on seabirds. Presented as part of the BirdLife State of the world–s birds website. Available from: http://www.birdlife.org/datazone
4. Frequency-rank distributions
5. Burger, J. (1988). Foraging behavior in gulls: differences in method, prey, and habitat. Colonial Waterbirds, 9–23.