Pollet, Ingrid L., Dave Shutler, John W. Chardine, and John P. Ryder. 2012. “Ring-billed Gull (Larus delawarensis).” The Birds of North America, edited by Paul G. Rodewald. Ithaca: Cornell Lab of Ornithology. Retrieved from the Birds of North America: https://birdsna.org/Species-Account/bna/species/ribgul doi: 10.2173/bna.33