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Nick Komar | profile | all galleries >> Birds >> Large Gulls >> Mystery Gulls >> Mystery Gull K - possible Slaty-backed Gull tree view | thumbnails | slideshow

Mystery Gull K - possible Slaty-backed Gull

I pulled these stills off a video tape that I made near Laie on the north coast of O'ahu, Hawaii, February 15, 2003. Click on the subgalleries below for more photos. Although Geoff Carey, a gull expert in Hong Kong, believed this to be a first-cycle Slaty-backed Gull (Larus schistisagus), other gull experts in North America were uncertain. SBGU appears to be expanding its range into North America, and the consequent increase in experience among North American gull observers has led to new opinions about this gull. Selected comments are posted below.
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Nick Komar 09-Feb-2006 07:19
I have received the following comments from experienced birders which support the identification of Slaty-backed Gull. More discussion and analysis by Christian Melgar can be found at:http://www.birdinghawaii.co.uk/XOahuGullArticle2.htm
Mar 17, 2003, --Geoff Carey, Hong Kong
It's not Vega Gull. The structure is wrong, the tail band too broad, the inner p window not as well marked as it usually is. I believe it is a 1y Slaty-backed Gull. The bulky, rather short-winged (at rest) structure, the overall uniformity, the relatively broad tail band with diffuse internal border, the poorly marked inner p windows, the darkness around the head and the largely dark bill are all good for this species in late inter….[Mar 26, 2003]… I note also the legs are rather dark and liver-coloured, which is good for SBGU. … SBGU in 1y plumage doesn't seem to actually have an ALL dark tail; usually there are pale basal corners. However, it is also a very variable species, and a significant number of birds show a tail band, if a very broad and diffusely-bordered one.
Jan 22, 2006, --Alvaro Jaramillo, San Francisco Bay Bird Observatory
I think that this is a great candidate for a Slaty-back. The feature which is not standard is the extensive pale base to the tail, which suggests other Old World taxa. However, those Old World taxa should not show the pale and poorly marked greater coverts and the extensive pale on the underside of the primaries (pale inner vanes to primaries) with a narrow blackish terminal stripe on the tips of the primary undersides. In terms of structure, bulky with short, widely spaced legs, parallel sided bill and so forth it looks good for Slaty-backed. I am not clear on what heuglini looks like at this age, but imagine it would have a longer winged structure, slightly slimmer, longer legged, darker undersides to primaries, darker inner primaries on upperwing and darker greater coverts. Having said that it is easier to reconcile pale bases to outer rectrices on a Slaty-back, than
all of the other missing features for something like Vega or heuglini.

Jan 23, 2006, --Peter Pyle, Point Reyes Bird Observatory
Dave DeSante and I agree that it was most likely a Slaty-backed Gull. In addition to the points that Al mentions, the dark outer webs to the outer rectrices is a good mark for Slaty-backed vs. Vega Gull. In helping my Dad with his monograph I have recently reviewed all gull records from Hawaii. There are 12 substantiated Slaty-backeds (of 15
individuals) from Midway and Kure and one specimen from Barber's Point, O'ahu, found dead on 20 April 2000 (BPBM 184288). There are several other sight records from the Main Hawaiian Islands that could be Slaty-backeds but were not well-enough documented in our opinion. Some of these were reported as adult Western Gulls. Vega Gull is regular in winter in the Northwestern Hawaiian Islands (35+ records including 19 specimens) and a specimen from Maui represents the only substantiated record from the Main Islands.

Feb 8, 2006, -- Osao and Michiaki Ujihara, Japan
We feel the gull is a Slaty-backed Gull. The moderate darkness of the primaries,
and somewhat uneven overall coloration (such as streaky neck) look very nice. In comparison with our own "typical" or "average" image of the species, the bill seems to be a bit slimmer, and the dark tail band seems narrower. But we feel both are safely within the range of known variation.

Additional comments welcome.
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