Identification of Slaty-backed Gull Larus schistisagus: a North American Perspective

First-winter Slaty-backed Gull Larus schistisagus, Busan, February 16th 2015 © Nial Moores

For those who are really into the wonderful world of gulls and gull identification, the following paper in Birding on Slaty-backed Gulls might be of some interest:

http://www.birdpop.org/DownloadDocuments/McKee+Pyle+Moores-2014-SlatyBacked-Gull-plumages-Birding.pdf