Canon PowerShot SX50 HS
Digiscoped with Panasonic DMC-LX5 | Nikon FieldScope III | 30XWA | hand-held (no adapter).
This is an adult in non-breeding plumage showing its pale yellow eye which helps distinguish it from non-breeding Black-headed Gull (C. ridibundus) of Eurasia. Two races usually recognized. African birds are C. c. poiocephalus. This is the nominate C. c. cirrocephalus found in South America which is marginally larger, slightly paler and has fainter head markings in non-breeding plumage. Formerly in genus Larus but moved to Chroicocephalus based on genetics. See SACC Proposal 250 for full details. HBW, Roberts, the African Bird Club checklist, and some older sources call this species Grey-headed Gull. Digiscoped with Panasonic DMC-LX5 | Nikon FieldScope III | 30XWA | hand-held (no adapter).
References:
Burger, J., Gochfeld, M., Kirwan, G.M. & Garcia, E.F.J. (2018). Grey-headed Gull (Larus cirrocephalus). 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 https://www.hbw.com/node/53989 on 14 January 2018).
Howell, S.N.G. & Dunn, J.L. (2007) Gulls of the Americas. Houghton Mifflin, Boston.
Howell, S.N.G., Lewington, I. & Russell, W. (2014) Rare Birds of North America. Princeton Univ. Press
Malling Olsen, K. & Larsson, H. (2003) Gulls of Europe, Asia and North America. Christopher Helm, London.