Posted by Phil Pickering (208.46.229.24) on October 21, 2001 at 13:02:07:
I'm still confused by a few of the features of this bird, but I have to guess that it's a Parasitic. It's obviously a fairly young bird, perhaps a 2nd calendar-year, but I wouldn't rule out a 3rd, since the vent and flanks seem so solid.
First, I don't really think that the R1s can be 1st-generation Long-tailed. I can't fathom how the comparatively straight-sided and blunt R1s of a juvenile Long-tailed could wear into a tapered shape with long barbs. I think the amount of taper suggests that the bases of the projecting sections of these feathers are a bit too wide for Long-tailed anyway. I don't know or have any resources with info on the shape of progressive generations of these feathers in Long-tailed, but I would guess that they would also be unlikely to have such long, sharp barbs, or such an inwardly-angled taper to their outer edges.
The projecting rounded tail feather (likely an R2) added confusion for me, but I'd suggest that more mature rects may actually be slightly longer than juvenile rects in these species. Combined with the potential that the other rects are extremely worn, this could perhaps explain the projection of the new feather. Just a thought.
The second main reason I'm going with Parasitic is that the dark coloration on the flanks and vent appears rather solid, AND seems to end in a well-defined latitudinal border with the base of the paler belly. The fairly sharp and straight definition of the border, and the strong contrast between the vent and belly seem much better for Parasitic to me. The flanks and vent are clearly not 1st-generation Long-tailed (would be obviously barred) and more mature Long-tailed seem to most frequently show a much less defined and straight border between vent and flanks, with the dark often extending up onto, and blending in with the belly. The vent is also typically grayer in Long-tailed than is apparent here, but the color could be off in the photo.
I tried, and could not get a feel for a measurable difference (in photos) between either the ratio of width of the wing base to tail length, or arm to hand length between Parasitic and Long-tailed. I'm sure there are differences that experienced observers can pick up on in the field, but I think they are probably too slight to be of much use in a photo like this where the foreshortened view might be deceiving. In general, I was struck by how remarkably similar these two species are in overall proportions (if not size), at least in young birds. That said, (factoring in the foreshortening) I do get a slightly longer, wider-winged feel than typical for Long-tailed from this bird. I think part of what I might be picking up on is actually the ratio of the size of the covert marking to the overall size of the wing. The markings seem fairly small and fine compared to the wing size here, while on most juvenile long-tailed they seem courser (larger) in proportion to the size of the wing. I might just be seeing things, too.
I think the markings on the underwing coverts are probably fairly whitish, mainly because the overall photo seems to have warmish tones due to the sun angle. I'm not sure this means much, though, as Parasitic are quite variable in this respect, and even more darkly-checkered birds might be quite faded this time of year.
Both immature Long-tailed and Parasitic can show a white base to the undertail.
Finally, the greater extent of the dark on P10 of this bird does seem to be more typical of Long-tailed, but this seems so variable in both Long-tailed and Parasitic to me that I would have a hard time feeling confident about using it as a definitive mark, particularly in light of the shape of the R1s.
Cheers,
Phil