| Comments on Possible 1st-cycle Slaty-backed Gull (Larus schistostagus) at Redbud Park, Clearlake, Lake County, CA, 15 December 2007. If you wish to add a comment and want to be identified with your comments, please let me know! Otherwise you'll be anonymous. |
| Respondent 1: Birder from California (member of CBRC) I'm having trouble getting to Slaty-backed on your Clearlake bird. The mantle does not look like retained juvenile and at least some of the feathers seem to be adult type and are pale gray. It is definitely an interesting bird, but I'm not sure what it is. Why not Herring X Glaucous-wing? Respondent 2: Birder from Washington I am far from an expert, though I guess we Seattletonians see about as many GW x HEGUs as anyone, and I'd probably have gone that way with this bird. But I really know crap about young SBGUs and a look at the Ujihara's website shows frightening diversity. I do know that they feel that many first cycle SBGUs in Dec/Jan show a white head and chest contrasting with a dark body, as in 30.6 in Howell's book. A visit to their website would probably be worthwhile. SBGUs have extensively pale inner webs to all primaries in first cycle, so if you saw the bird flap, that would help. But hybrid HEGU x GWGU might look that way. [Later] I need to learn to scroll down The wing pattern looks great for SBGU. The bird looks so different in each pic that it makes much hard to judge. I wonder if a SBGU would have so extensively replaced its back feathers this early in the year. In some of the photos, the bird does show that small head/big goose body appearance that seems unique to SBGU. I would ask Alvaro and the Ujiharas. Could a HEGU x GWGU look like this. Don't know. Thede Tobish might be of help there. I can't get a good enough feel from the photos for my limited skills to be applied. [Later, in response to a query about why a 1st-cycle Slaty-backed Gull was accepted in Washington] I guess our SBGU was accepted because of its shape (which should not be mimicked by hybrid) and that it matched "typical" SBGU. At some point, one has to say, if it matches one species in 5 or 6 key points perfectly, and is not a mismatch in any way, how likely is a hybrid to match that? Very unlikely. Especially given the number of ads and subad SBGUs that turn up. I suspect we miss a bunch of these birds thinking they are GW x somethings. Looking at the Ujihara's website is scary. Many of those birds I'd not have given a second look at, assuming they were GW x WE or GW x HEGU. Respondent 3: Birder from California (member of CBRC) Short answer: I don't know. Certainly a fun bird, but I don't think you can get more definitive than "possible". Ruling out a hybrid is pretty hopeless at this point when dealing with these first-cycle birds. The structure looks good. When you break it down, you can make a case for many pro-SBGU features. But this still doesn't help us get past the hybrid problem - Glaucous-winged x Herring, Slaty-backed x Vega, various back-crosses. Quite a mess really, with no resolution in sight. Anyway, back to your bird. Assuming the photos are representative, I wonder why this bird is so pale (primaries and tail aside). It doesn't look obviously bleached or worn, plus it is still fairly early in the season. The second generation mantle appears very pale. I would expect a SBGU to show darker centers or shaft streaks to some of these feathers. I guess I favor hybrid, but the fact remains, I can't be certain. Very nice bird, whatever it is! Respondent 4: Marshal Iliff (member of CBRC) This bird does not jive with me for Slaty-backed. The greater coverts looks a little too extensively smooth gray-brown for Slaty-backed to me, and recall Glaucous-winged. Since many (most?) Slaty-backed have a nearly fully dark bill through their second-winter, I think that the significant pale in the maxilla and base of the mandible probably indicate Herring Gull genes. Many first-winter Slaty-backed are showing paling in the eye even in the first winter and this bird looks to have a completely dark eye. Also, some of the scapulars look like they are gray with whitish fringes, and thus tending towards adult color. These scapulars would probably be darker in Slaty-backed. Nor do I think that the structure is quite right for Slaty-backed (not dumpy enough). As others have said, the primaries look consistent with Slaty-backed, but they are consistent with a hybrid as well and the legs are nice and pink. I'd consider this a probably Glaucous-winged x Herring. In this link on Alvaro's page note the following: 1) Note how dark the bill is on the second-winter that I photographed in January 2006; 2) Note how dark the centers to mantle and scapular feathers are; 3) note how pale the greater coverts are overall, without the extensive smooth gray-brown shown by your bird. My Response to Respondent 4 Your comments led me to scrutinize more carefully those photos from Japan: 1. Iris color: I am attaching a cropped image of an overexposed photo that shows iris-pupil contrast in good light in our bird. I'll post this on the webpage. I'm seeing slight pupil-iris contrast in a few Japanese birds as early as 13 January, but in most, including the March birds, the iris appears very dark. Of course a pale iris might not be unexpected in a hybrid with Herring Gull genes, so I'm personally unconvinced that iris color is meaningful at this age. 2. Bill color: I'm seeing slight brown between the nostrils and at the base of the mandible on Japanese birds as early as 1 November. Many have more extensive paleness on the bill by 13 January and 3 February. I don't think paleness on the bill is necessarily indicative of Herring Gull genes. 3. Mantle feathers: I agree the mantle feathers are very pale. Many of the whitish Japanese gulls have relatively pale mantles, but all seem to have more extensive dark markings, even when bleached in March. 4. Greater covert coloration: There is extreme variation in the Japanese birds. 1 November birds have smudgy brown or checkered greater coverts. Some have very pale greater coverts by 13 January [oops, I overlooked 14 December photos showing pale greater coverts], but there are still many with smudgy brown or checkered coverts on 3 and 16 February. The greater coverts are bleached white on most by 15 March, but some still retain dark coverts, even some checkering (see page 2 of 15 March photos). [I took another look at the photos and a few, including some on 13 January, have similarly "smooth gray-brown" on the greater coverts.] |
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