Hi All: Entertaining gull discussion. The structural characteristics typified as stout bodied* for slaty-backs got me interested because the skeletons of similar sized gulls exhibit little interspecific differences. This is not a web fact, but based on extensive analysis published in peer-reviewed journals. The point being this provides the basis for expressing surprise and skepticism that a slaty-back could be id?d by structure.

I had assumed the structural characters cited for slaty-backs were web induced allusions wafting from California gull watchers (http://www.coastside.net/chucao/gulls/Slatyback.htm). However, these characters predate the web and are mentioned in Harrison and detailed more extensively on a website specifically dealing with identification of slaty-backs (http://www.birdskorea.org/Birds/Identification/ID_Notes/BK-ID-Slaty-backed-Gull.shtml). Add wide-stance and ?sumo-wrestler? like to the description. Looking at the images on the site, some birds seem to fit the characterization in the text, but many do not. Nial Moores, the creator of the site, adds the interpretation that the characters are adaptations to lower the center of gravity for life on wind swept rocky coasts, but this habitat hardly seems unique to slaty-backs. Given that Moore has experience with positively id?d slaty-backs, I?m willing to accept his judgment that slaty-backs differ in some way from the glaucous-winged and vegae herring gulls that he had for comparison. Harrison suggests that slaty-back appears heavy bodied, similar to a diminutive greater black-backed. Moores suggests ?alert birds often stretch the neck and adopt a characteristic pot-bellied posture? and Olsen and Larsson repeat this, but picture 510 of Olsen and Larsson is of an adult with a stretched neck that doesn?t look pot-bellied. Typically gulls in Upright Alert sleek feathers prior to flight. In general images in Olsen and Larsson and Howell and Dunn don?t lend any credence to a species typically structural difference for slaty-backs.

Assuming no skeletal differences, how does one get a stout-bodied gull? For an example, there is a 2nd winter that looks stout and goose-like (from 15 Dec 2005 at http://www.coastside.net/chucao/gulls/Slatyback.htm). The "goose-keel" referred to in the text is actually the distended abdomen on this bird. Based on experience of skinning and defatting many winter gull specimens, the "keel" is fat. There is no skeletal structure in this region. This abdominal region and the breast/furcula are major areas for fat storage, which can be up to 1 cm thick and could give a gull a stout-bodied profile. As for short legs, published measurement for tarsi are no different from westerns, but the focal bird appears to be short-legged, similar to a sumo wrestler. Perhaps some gulls are fatter than others and look short-legged? Other examples are at http://www.coastside.net/chucao/gulls/Slatyback07.htm#adult07 of another second winter and an adult. The 2nd winter does appear stout, but there is also a stout or fluffed up glaucous-winged in the background of the first picture. However, the adult does not appear stout, short-legged, or short winged and the text details why the bird is a slaty-back without mention of the stout characteristics. For additional examples, peruse of the Birds of Korea (url above) site and Japan gull site (http://larus.hp.infoseek.co.jp/slayty.html) as well as the gull books.

In summary, there is ample mention of the stout-bodied character of slaty-backs, but as yet there is no systematic documentation.

*also dumpy, goose-like, goose-keeled, stocky body, barrel chested, short-winged

Gary Shugart, Slater Museum of Natural History University of Puget Sound Tacoma, WA 98416 (home) gshugart at ups.edu; http://www.ups.edu/slatermuseum.xml http://digitalcollections.ups.edu