Hybridisation in gulls
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Hybridisation in gulls occurs quite frequently, although to varying degrees depending on the species involved.
Hybrid large white-headed gulls
- Herring gull and lesser black-backed gull interbreed to a limited degree where their ranges overlap, producing birds of intermediate appearance, which could be confused with yellow-legged gulls.
- Western gull and glaucous-winged gull hybridise extensively in western North America. Evidence of genetic influence of each upon the other is found throughout the range of both species. This particular hybrid is sometimes known as the "Olympic gull", or "Puget Sound gull".
- Herring gull and glaucous gull hybridise to a limited extent in Greenland and Iceland. The offspring have been termed "Nelson's gull", but are sometimes also known as "Viking gull".
Hybrids among the small hooded gulls
- The most common hybrid found among gulls in Europe is between black-headed Gull and Mediterranean gull. Hybrids of this combination are occasionally reported on the northwestern edge of the breeding range of Mediterranean gull.
- Birds have also been reported in Europe which have been suspected of being Mediterranean gull × common gull hybrids; one such bird gull seen in Lincolnshire in 2002 
- A bird seen in December 2001 at Belhaven Bay, Lothian, and present each winter since (until at least 2005/6) is believed to be a hybrid between black-headed and common gulls 
- Steve N. G. Howell, Jon Dunn (2007). A Reference Guide to Gulls of the Americas. Houghton Mifflin Harcourt. p. 479. ISBN 0618726411.
- Malling Olsen, Klaus and Hans Larsson (2003) Gulls of Europe, Asia and North America Helm Identification Guides ISBN 0-7136-7087-8, page 193-4
- Tarrant, Mike (2002) An apparent hybrid gull in Lincolnshire Birding World Vol. 15 No. 6 p247
- Gillon, Keith (2006) An apparent hybrid gull at Belhaven Bay, Lothian Birding Scotland Vol. 9 No. 2 p92