jaeger

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: To answer my own ignorance about molt in larus gulls, the 1st post-juvenile molt does NOT include the undertail coverts (or typically the vent and belly). These 1st-generation feathers are not replaced till the first complete molt, which doesn't even commence till late April or May of the 2nd calendar-year in Western Gulls (Howell & Corben), and I think likely has an even later timing in northern-nesting species like Thayer's. I'm not sure if this particular fact applies to jaegers, but I do suspect that Tony is correct in that juvenile jaegers retain their 1st-generation flight feathers (at least) into the summer of their 2nd calendar-year. I think the extremely worn immature jaegers that occasionally show up in summer in the US (Kaufman) are most likely to be year-old birds with partially retained juvenile plumage, most obviously the flight feathers. Molt in jaegers is something I'd like to learn more about - guess I'll have to fork out the ~$40 for Olsen and Larsson. : To my eye, the primaries of this bird appear a bit rounded, but given the month, they actually don't appear to show nearly the amount of wear you would expect if they were retained juvenile (1st-generation). Given their unfrayed appearance, combined with the somewhat more adult-like appearance of the vent and flanks, I strongly suspect that it's much more likely that this is an older subadult bird (3rd calendar-year+) rather than a year-old bird. I think this also might be supported by the somewhat lengthy projection and overly pronounced barbs of the R1s for a juvenile Parasitic (in my limited experience). Harrison states that both Parasitic and Long-tailed can still show patterning to the underwing coverts in 2nd-generation+ plumage, so their appearance here doesn't necessarily indicate that this is more likely to be a year-old bird. : The reason I ramble on about this is that both Harrison, and apparently Olsen and Larsson (Matthew Kenne's point) indicate that post-juvenile (2nd-generation+) primaries on Long-tailed most typically show a "reduced or lacking" amount of white at their bases, while the amount of white is still extensive in post-juvenile Parasitic. In essence, the comparatively extensive white at the bases of the (apparently) 2nd-generation+ primaries of this bird seems to be a very strong mark against Long-tailed (based on those sources, anyway). : A couple sources also point out that immature Long-tailed have comparatively straight barring on the vent and surrounding area, while the barring on Parasitic tends to be more wavy and irregular. Tough to judge, but I think there is faint barring apparent on the vent and flanks of this bird, that appears somewhat irregular to me. : Also, to expand on a previous point - in Long-tailed the barring in juveniles, and the darker gray in adults more often (not always) extends from the vent and flanks onto the belly (and sides), ending or blending at a point well in front of the base of the legs. In pale-morph Parasitic this seems less variable, with the juvenile barring, or dark gray-brown in adults most typically ending AT the base of the legs, or slightly posterior to that point. Because this photo is so foreshortened, it is hard to judge where the point of the break in color really is. But - I think the obvious mark on the lower belly that seems to be surrounded by a small "bowl" of convex or concave feathering is the leg base (point where the legs would extend from on a standing bird). The fact that the dark of the vent and flanks ends in such an (apparently) neat, straight border with the pale of the belly, very slightly posterior to the (apparent) leg base, would seem to be a fairly precise match for a "typical" pale-morph Parasitic. This IS variable, but I feel it's probably (at least statistically) one of the better supporting marks for Parasitic apparent in this photo. I also think the feet extend quite close to the tail tip for a Long-tailed, but that's undoubtedly too posture-dependant to be more than a minor supporting mark. Ditto for the rump, which appears a bit wide for Long-tailed to me. : Cheers, : Phil

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