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

(last update: December 2015)

hybrid Glaucous-winged x Western Gull (glaucescens x occidentalis) 1st cycle (2CY), January 25 2011, Everett, 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 (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. 

This bird is much like a first-cycle Western Gull, but the folded primaries are not dark enough and tipped pale. Its bill is heavy for American Herring Gull x Glaucous-winged Gull hybrid, and the hint of a dark mask is suggestive of Western Gull heritage.

Steve captured the same bird in flight, where he points out that you can see that the pale on inner webs of the primaries is too extensive for pure Western Gull. The wingtips are much too dark for Glaucous-winged Gull. American Herring Gull x Glaucous-winged Gull hybrid would usually have a more obvious pale panel on the inner primaries.