This is a second cycle bird showing some dark mantle feathers, pale eye and pale bill base. This rather bulky, large gull species is endemic to the Northwest Pacific Ocean. It is a rarity in North America but difficulty in field identification makes its status problematic. This photo conveys their rather dumpy, thick-necked, heavy-chested look. Immatures come in a bewildering variety of plumages. Many of the first cycle birds we saw would likely not be identified as Slaty-backed if seen in North America. In particular some individuals may be confused with various Glaucous-winged Gull hybrids including Glaucous-winged X Herring and Glaucous-winged X Western.