Slaty-backed Gull (schistisagus) / オオセグロカモメ / 큰재갈매기

(last update: December 2015)

Kim Seog-min (South Korea)
Hideo Shimura (Japan)
Peter Adriaens (Belgium)
Mars Muusse (Netherlands)

hybrid Glaucous-winged x Western Gull (glaucescens x occidentalis) 2nd cycle (3CY), January 31 2011; Mukilteo, Snohomish Co. - Washington, USA. Picture: Steve Mlodinow.

Please visit Steve's Flickr photostream, for many more images. And also Dave Appleton's blog on hybrids!

There is an extensive overlap between the ranges of Western Gull and Glaucous-winged Gull and in that overlap zone (between southern British Columbia and southern Oregon) the two species readily hybridise.  Hybrids (also known as Olympic Gulls) are not only fertile but in the centre of the zone they have superior fitness over pure birds.  Consequently there is a hybrid swarm of birds showing the full specturm of appearance between the two pure species. 

Wingtips and back too dark for pure GWGU. Wingtips and back not dark enough for WEGU. Bill stout, primaries short, unlike GWxHEGU, which would also typically have paler mantle.