Hybridisation in gulls
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Hybridisation in gulls occurs quite frequently, although to varying degrees depending on the species involved.
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Hybrid large white-headed gulls
- European herring gulls and lesser black-backed gulls interbreed to a limited degree in their wide area of range overlap, producing birds of intermediate appearance, which can be confused with yellow-legged gull.[1]
- Lesser black-backed gull has interbred with yellow-legged gull on a few occasions in England, Germany, and the Netherlands.[1]
- European herring gulls and glaucous gulls hybridise in Iceland and Greenland. The offspring have been termed "Viking gull".[2]
- Western gulls and glaucous-winged gulls hybridise extensively in western North America between Washington and Oregon. This particular hybrid is sometimes known as the "Olympic gull", or "Puget Sound gull".[3] The persistence and backcrossing of hybrids is believed to be due to hybrid superiority, where hybrids exhibit higher evolutionary fitness than parent species in the hybrid zone. [4]
- Great black-backed gulls and American herring gulls have hybridised in eastern North America, particularly the Great Lakes. This hybrid is sometimes known as "Great Lakes gull".
- American herring gulls and glaucous gulls hybridise in Alaska. The offspring have been termed "Nelson's gull".[2]
- American herring gulls and glaucous-winged gulls hybridise extensively in southern Alaska. The offspring are sometimes termed "Cook Inlet gull".
- Glaucous-winged gulls and glaucous gulls hybridise in western Alaska. These hybrids are sometimes called "Seward gull".
- American herring gulls and kelp gulls have hybridised in Louisiana. This combination has been termed "Chandeleur gull". This hybrid is interesting as Louisiana is outside of the normal breeding range of both parent species.
- Glaucous-winged Gull and Slaty-backed Gull hybridise in western Alaska and possibly eastern Siberia. A name for this combination has been emerging as "Commander" Gull, after the Commander Islands off of eastern Russia. Some speculate most Glaucous-winged Gulls wintering in Asia have hybrid origins.
- It is believed by some that the Kumlien's subspecies of the Iceland gull may be a hybrid population between Iceland gulls and Thayer's gulls. No pure Thayer's gulls are known to occur within the range of Kumlien's although many Kumlien's within their range are almost indistinguishable from Thayer's gulls, while others look like pure Iceland gulls with a range of variation in between.
- A hybrid between lesser black-backed gull and ring-billed gull has been seen over a period of several years from 2012 to 2025 in the English Midlands; a similar bird has also been seen in Spain during the same period.[5][6]
Hybrids among the smaller gulls
- The most common hybrid found among smaller 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.[7]
- Hybrid Mediterranean gull × common gull has also been recorded more rarely;[7] one such gull was seen in Lincolnshire in 2002.[8]
- 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.[9]
- More rarely, hybrids have been reported between laughing gull and black-headed gull, laughing gull and ring-billed gull and possibly black-headed and ring-billed gull. All have been reported from eastern North America.
- Common Gull is known to have hybridised with Ring-billed Gull in Northern Ireland.[10]