ML613004653

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Sex

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Observation details

Addenda - I’ve spent considerable time on this, reviewing photos, videos, text resources and soliciting opinion from experienced birders. So far, all opinion has been Ross’s Gull, some unequivocal, some with caveats. I was able to get the opinion of John Puschock - having lead many trips to Alaska and with extensive experience with the species, having seen many thousands. He said the bird looked good for Ross’s, GISS was fine, while realizing the limitations of the media. I certainly have to put stock in that, as I’ve never seen the species and he would have a far better grasp on the gestalt of the bird in the video. I’ll post this as ROGU at some point to continue the discussion. It will remain unconfirmed for now but any additional (informed) opinion is valued. I’m hopeful of getting some feedback, especially from observers with field experience with ROGU, especially those that may have observed the species during sea watches or other flyby circumstances similar to this observation. Those with a good understanding of the flight style / GISS of this species would be most valuable. If you can contribute, you can either flag the media (it will show up in my review), or email me directly at jmholdsworth@rogers.com. Declaratory statements, without supporting rationale, are not needed. I’m keeping this off social media discussion groups, to avoid the white noise produced by such scrums, as I find most to produce rather circular discussions that don’t yield much insight. Please do not link this checklist or post elsewhere without my permission. 1st basic. I dismissed this bird initially as my only view of it was through my viewfinder and it was a speck in my video. It was only, much later, after viewing some flyby videos of ROGU that it triggered something, and I went back and heavily cropped the video. Inspection revealed a bunch of traits suggesting ROGU over LIGU, and here we are. My initial impression of the bird in my video was a small, rather bob tailed gull, lacking the rather elongated and long tailed look of ROGU. My review of what is likely every video ever produced of 1st basic ROGU surprised me - these birds, at some distance, almost always appeared short tailed, especially in profile, as the central tail feathers tend to be lost from view. I’ve linked a video further down that illustrates this impression. The general compactness of the bird was also, initially, off-putting, but (again) this seems to be genuine, when reviewing other media. I’ve produced a series of video crops that illustrate relevant features and I will discuss each crop separately. After that, I will discuss the actual video sequence. The entire sequence is overexposed due to the bright conditions of the day…allowances are made for this circumstance. Crop 1, 2 - small, pointed winged gull with striking upperwing pattern, significantly with blob of black in central rectrices, while most outer rectrices appear to be white. Crop 2 (shot through branches) included to illustrate that this feature appears stable in the video. In fact, it appears exactly as this in numerous frames, so not an artifact, but disappears in profile. There are no frames that show any black on any outer rectrices. Upperwing very high contrast, with outer 2 or 3 primaries entirely dark to the tip, inner primaries more dusky basally but strikingly marked white near the tip, creating a bold, white intrusion from the secondaries to almost the outermost primaries. Greater and median primary coverts blackish, median secondary coverts blackish to the tertials, lesser secondary coverts very pale. All secondaries appear white as do most inner primaries. Mantle looks white but some frames show a bit of contrast with the white uppertail, so assumed very pale gray. I’ve included a grab in the LIGU record to illustrate what is blown out and what is likely not, noting the LIGU was seen at the same time, exact same conditions / angle as our subject (see video). As you can see, the LIGU shows marked contrast between mantle and primary tips and trailing edge, as well as showing pronounced post ocular blotch, and a bit of a dusky crown. There are no frames that show any dusky crown nor post ocular on the subject bird. What is consistent is the appearance of a small “mascara smudge” adjacent to / behind the eye. Crop 3, 4, 5 - sequential series, shows some central tail projection, that is stable through a series of frames, but disappears in profile. I’m not entirely sure what I’m seeing here, apart from the tail looks fairly long (comparing head projection to tail projection), slightly wedged and there is a projection, although with no black visible now. The black central tail feathers and features discussed here are all visible in the video, but angle and light makes them transitory. As I prefaced, my initial impressions of this bird was relatively short tailed but certain angles indicate otherwise. In terms of how light is affecting things, I’d acknowledge there is blowout and some detail is lost. The upperwing contrast is likely exaggerated, although as shown by the LIGU pic, only slight grays would be eliminated. Things like the white head, black central tail feathers and sequence showing the tail shape, would seem to be unaffected by excess light. The underwing is another story. If you look at the Jaeger crops, the underwing and undertail (which were quite dark) are blown out. Video - the subject bird appears compact, with a small, rounded head, cylindrical body shape and pinched rear. The bob tailed appearance is not supported in crops of the dorsal, and (as mentioned earlier) video of distant ROGU share this impression. See here, the only video I could find of actually migrating birds. https://www.youtube.com/watch?v=GNRSzkmPxF4 Here is a photo (not mine) that shows how short tailed 1st cycle birds can look in profile. https://media.ebird.org/catalog?taxonCode=rosgul Flight GISS is remarkably dissimilar to the adjacent adult Little Gull. Not only is the stroke rate discernibly quicker (calculated at intervals, ranging from 30 - 35% quicker), but dynamic range differs as well. Subject birds upstroke ends lower, while downstroke is dramatically more shallow than LIGU, barely breaking the plane of the body. The result is the impression of greater urgency, stronger, more linear flight with a piston-like, flickering stroke that is near vertical. The LIGU can be seen to have a nearly rowing, circular cycle, producing more bob with each stroke. The subject bird was also faster than the LIGU, easily passing it en route to the Cape. Subject bird shows strong wing angle at the wrist, with hand swept back in flight. Harrison described ROGU as unique in flight, with strong pigeon like flight, and I get the same impression of the subject bird. Question is, could the difference in wing structure between 1st cycle LIGU vs adult, account for this different GISS? My media search of video of 1st cycle LIGU still showed a very deep downstroke and decidedly languid appearance. Certainly the subject bird imparts none of the buoyant GISS that I've noted, even in birds in 1st cycle. (I've had 64 individual records of LIGU since moving here in 2019, so I am familiar with the species and have seen numerous individuals in lakewatch situations, including at least a dozen in 1st basic.)

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