Showing its bright yellow bill and deep red orbital ring, this adult is in breeding plumage. This race breeding race in Western North America is the smallest and has a relatively thinner bill compared to Old World populations. Note large white mirror on underside of P10. Eye generally dark but variable. Genetically distinct American population sometimes separated under the name "Short-billed Gull." Canon PowerShot SX50 HS.
References:
Burger, J., Gochfeld, M., Kirwan, G.M., Christie, D.A. & Garcia, E.F.J. (2017). Mew Gull (Larus canus). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from http://www.hbw.com/node/53970 on 13 July 2017).
Howell, S.N.G. & Dunn, J.L. (2007) Gulls of the Americas. Houghton Mifflin, Boston.
Malling Olsen, K. & Larsson, H. (2003) Gulls of Europe, Asia and North America. Christopher Helm, London.
Moskoff, William and Louis R. Bevier.(2002).Mew Gull (Larus canus), The Birds of North America (P. G. Rodewald, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America: https://birdsna.org/Species-Account/bna/species/mewgul