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

(last update: December 2015)

Slaty-backed Gull (schistisagus) adult January

Gulls of Europe, Asia and North America

by Malling Olsen, K. & Larsson, H.
Christopher Helm, London, 2004

"we" in the text below refers to the original authors. If any errors occur in this text, please let me know and mail to marsmuusseatgmaildotcom.

On these webpages you'll find captions "hybrid Glaucous-winged x Herring Gull (glaucescens x smithsonianus)" and "hybrid Glaucous-winged x Western Gull (glaucescens x occidentalis)", used for the “Cook Inlet Gull” and the "Olympic Gull" respectively. One should remember that it's a misconstruction to believe that one of the individual’s parents was a pure Glaucous-winged Gull, and the other was a pure Western or pure American Herring Gull. That's a reconstruction we just don't know for certain. In reality, many of these birds are the products of intermediate parents, hence the prefix "hybrid".

Identification of Slaty-backed Gull (schistisagus)

PART 1: description of adults (this page)
PART 2: description of 1st cycles
PART 3: description of 2nd cycles
PART 4

PART 1: description of adult birds

Length 61-66cm, wingspan 145-150cm. A large gull from N Asia, the only large dark-backed gull in its breeding range. It is stocky with rounded head, rather straight thick bill (at most with poorly marked gonys-angle) and rather strong but often short-looking pink to rosy legs. Alert birds often stretch the neck and adopt characteristic pot-bellied appearance. Wings are rather short in settled birds. In flight heavy with full neck, broad arm, but rather short pointed hand and often slender hindparts. Males may approach jizz and size of Great Black-backed or Glaucous Gull, smallest females approach Herring and Vega Gull.

Slaty-backed Gull (schistisagus) adult, January 02 2010, Choshi, Japan (Chris Gibbins). Classic adult bird in upperpart tone, overall structure, and bare part colours (though its bill is rather slender).	Great Black-backed Gull (marinus) 1EJ  6CY, January 27 2015, Bulloch Harbour, Ireland (Graham Prole). Resembling Slaty-backed posture.
Glaucous Gull (hyperboreus) 1st cycle (2CY), March 08 2016, Scheveningen, the Netherlands (Mars Muusse). Note short-winged jizz.	Herring Gull (argentatus) NOS 486900 32CY, January 07 2016, Boulogne-sur-Mer, France (Jean-Michel Sauvage). Compact bird. Note position of eye, compared to Slaty-backed.
Slaty-backed Gull (schistisagus) adult, December 25 2013, Hokkaido, Japan (Ian Davies). Arrows indicate 'string of pearls', which are the white tongue tips most obvious on P6-P8.	Great Black-backed Gull (marinus) adult, February 24 2016, IJmuiden, the Netherlands (Mars Muusse). Arrows indicate lack of such a string of pearls; here no white tongue tip on P8 and only thin white crescents on P6-P7.

In all ages, outer wing pattern offers best clues; wing-tip appears streaked with pale line of dots, as primaries (apart from P9-P10) have pale inner webs and mid-primaries broad white tongues, a pattern only matched to such a clear degree by certain hybrid gulls (Glaucous-winged x Western Gull, Glaucous-winged x American Herring Gull). Western Gull of the paler-mantled occidentalis shows heavier bill with more bulbous tip and squarer head, with eyes sitting higher on head. American Herring and Vega are slightly smaller and less heavy with slimmer bill and generally longer wings. Adult upperparts are much paler than in Slaty-backed and wing-tip darker.

Adult has slaty upperparts, slightly darker than Western Gull nominate occidentalis. Wing-tip diagnostic: black with pale inner webs to primaries and large white tongues, forming 'string of pearls’ which gently tapers away towards wing-tip. This is obvious in head- or side-view from below, and dark tips to outer primaries as dark trailing edge to outer wing. P10 and sometimes P9 have white mirrors; 5-7% have white tip to P10. Shows broad white trailing edge to inner wing, broader than in other large gulls apart from Great Black-backed and Kelp, which have blackish upperparts. The trailing edge merges with white tips to P1-P5 in flight. In settled birds, broad white scapular and tertial crescents are most noticeable, tertial crescents connecting to slightly narrower but striking white line on secondary tips. Wing-tip in settled birds similar to Western Gull, with 4-5 white primary tips beyond tertials, and 2-3 beyond tail-tip. In some there is a slight gap between inner two and exposed outer 2-3 primaries. Eyes pale (sometimes dark-peppered), surrounded by purple to deep pink orbital ring. Legs raspberry to rosy or pink.
In flight the adult wing pattern is striking. Caused by grey inner webs to primaries, the underside of the wing-tip looks mainly grey with black limited to tips, and the conspicuous white ‘string of pearls’ dulled somewhat by pale surroundings.
In summer, bill similar to Vega and American Herring, but generally paler orange-yellow. In winter, bill duller: base of bill often pinkish from Aug, and frequently bill shows narrow dark subterminal markings. Head and breast-sides heavily brown-spotted or -streaked, often with dense streaks around eye forming elongated dark mask, narrowing in front of pale eye. Legs pink, often raspberry-pink to rosy.
The rather dark upperparts make confusion with Western Gull highly probable. Western of similar size, but head heavier, bill with more bulbous tip, eyes are smaller and darker, and placed further back and higher on head, and wing-tip is more solid black with white mirror on P10 only and black wedges to all primaries; at most shows ‘string of pearls’ in mid-primaries and – from below - much fuller black hand than Slaty-backed. Furthermore, upperparts are less bluish-tinged, legs duller flesh and head mainly white in winter. Vega and American Herring Gull generally smaller with paler grey upperparts (darkest in Vega) and more solid black wing-tip, typically lacking pale streaks and line of spots: the character is not foolproof, as some Vega and American Herring show limited black on wing-tip, and some Slaty-backed lack white subterminal spot on P8. Hybrid Western x Glaucous-winged Gull with outer wing similar to Slaty-backed identified in winter by weaker, greyer, dark head-markings, more diffuse rather than spotted or streaked, squarer head with eyes places higher on head, and bulbous tip to heavier bill.

Slaty-backed Gull (schistisagus) adult, March 28 2008, Hokkaido, Japan (Shiroto). Orbital ring pink, small red gonys spot on yellow bill and blue-yellow iris. Broad tertial crescents and secondary tips. Upperparts grey tone about equal to graellsii Lesser Black-backed Gull. Strong pink, short-looking legs.	Slaty-backed Gull (schistisagus) adult, December 26 2013, Hokkaido, Japan (Ian Davies). Orbital ring pink, vivid gonys spot on yellow bill and yellow iris with much speckling. Broad tertial crescents and secondary tips. Upperparts grey tone about equal to graellsii Lesser Black-backed Gull. Pink legs. Strong pink, short-looking legs.
hybrid Glaucous-winged x Western Gull (glaucescens x occidentalis) adult, December 07 2015, Eureka waterfront, CA (E Fox). This basic adult bears most resemblance to Western Gull, but with much smudge on the head.	hybrid Glaucous-winged x Western Gull (glaucescens x occidentalis) adult,December 03 2008, Vancouver Island, BC (Guy Monty). Pigmentation on primaries intermediate, and grey tone upperparts intermediate.
hybrid Glaucous-winged x Western Gull (glaucescens x occidentalis) adult, February 16 2009, Portland, Oregon (Lyn Topinka). Purple orbital ring and extensive speckling in iris (>75%). Medium grey primary pigmentation, obviously darker than upperparts may be indication for occidentalis influences. Upperparts too dark for pure Glaucous-winged. Also primaries too dark, but not black as in occidentalis. Pure occidentalis would not show head mottling (at all in winter).	hybrid Glaucous-winged x Western Gull (glaucescens x occidentalis) adult, January 14 2011, Mukilteo, Washington, USA (Steve Mlodinow). Obvious smudge on head and primaries almost blackish in resting bird, but compare to next image where pigment on outer primaries appear rather greyish, not solid black and only treaching to primary coverts on outer web of P10, not on P9-P8.
hybrid Glaucous-winged x Western Gull (glaucescens x occidentalis) adult, November 20 2010, Westport - Washington (Steve Mlodinow).Resemblance to Slaty-backed Gull x Glaucous-winged Gull hybrid. Most of those would show more streaking (vs. smudging) on head and neck than seen on this bird, but on the other hand, there is more streaking here than is typical for Western Gull x Glaucous-winged Gull. The black on outermost primaries is more extensive than would be seen on Slaty-backed Gull x Glaucous-winged Gull, the white "tongues" should be more extensive - it should extend to P8 - and P9 would most commonly have a white mirror on Slaty-backed Gull x Glaucous-winged Gull.	hybrid Glaucous-winged x Western Gull (glaucescens x occidentalis) adult, October 28 2011, Elwha River Mouth, Clallam County - Washington (Steve Mlodinow). This hybrid combination may show pigmentation on the wing-tips being more extensive and a tad darker than on a pure Glaucous-winged Gull. It can show head and neck markings of a basic plumaged Glaucous-winged Gull but a mantle color that is more Western-like. The bird below is somewhat like Western Gull, but Steve points to the dark eye and heavy markings on the head and chest. Western Gulls should be white headed/chested, or nearly so. Many/most have pale eyes, though this is highly variable.
Western Gull (occidentalis) 2406-14050 12CY, December 13 2015, Eureka waterfront, CA (E Fox). Mature Western Gull with smudging on the head, banded as a chick on the Farallons. Do Olympic Gulls breed south of Washington?	Western Gull (occidentalis) adult, March 24 2007, Newport, Oregon (Greg Gillson). No black on bill, rather pale iris, saturated orange-yellow bill.
Western Gull (occidentalis) adult, February 17 2009, Beaverton, Oregon (Greg Gillson).	Western Gull (occidentalis) adult, March 08 2009, off Dana Point, Orange Co. (John Avise).
Similar size to Slaty-backed, but Western has upperparts slightly paler or similar in shade (Kodak 8-11), but white primary tips smaller at rest, bill more bulbous-tipped and typically brighter in winter (orange-yellow, without dark distal marks), orbital ring yellow, eyes often dusky, and, in winter, has little or no dusky head and neck streaking. Also note Western’s narrower white trailing edge to secondaries, narrower and more restricted whitish tongue-tips and mirrors on outer primaries, and blackish underside to wingtip.

CONTINUE PART 2: 1st cycle birds >>>