We encountered a dark juvenile jaeger on last weekend’s Mississippi Canyon pelagic birding trip out of Venice, Louisiana. The bird was far offshore, near the edge of the canyon. We identified it as a possible Parasitic Jaeger (Stercorarius parasiticus) in the field, but of course, identification of jaegers is very complex, and as photographs made the rounds over the last week, they sparked quite a bit of discussion. I’ve pulled together several images of the bird here, thanks to four generous photographers. Images belong to them and are used with permission.
Zac Loman got a great shot of the bird on the water. It’s a very dark individual, lacking much of the streaking and barring typical of lighter and intermediate birds. Its outer primaries show no pale tips. The undertail is barred with brown and a pale orange-buff/cinnamon color. Parasitic Jaegers that are this dark look very similar to dark juvenile Pomarine Jaegers (though can Pomarines this dark show orange/cinnamon tones?). Note that structurally, the bird looks small headed with a slender neck and a fairly slim bill.
Much discussion centered on two features: the bird’s greater under primary coverts and its central rectrices (tail feathers). Interpretation is highly contingent on the quality of the photographs; for example, in this distant shot by Erik Johnson, the bird appears to show pale-based coverts — creating a “double flash” on the underwing — and blunt-tipped central rectrices, both of which support an identification as Pomarine Jaeger.
In this shot by Dave Patton, the central rectrices also look blunt.
But this Dave Patton shot shows the greater under primary coverts more clearly, and they do not appear to be extensively pale-based. Instead, they seem fairly heavily barred, though this shot has some motion blur on the wing. Note that juvenile Parasitic Jaegers can show barring on these coverts (see this striking example). But juvenile Pomarines can show extensively pale bases to these coverts, perhaps with faint smudging but contrasting strongly with the median under primary coverts and barred and dark only on the outer portion (see here and here).
Here’s another look at the underwing in this shot by Justin Bosler.
And this money shot, also by Justin, shows the underwing again but is also the best shot I’ve seen of the bird’s central rectrices, which appear at this angle and in reasonably sharp focus to be pretty sharply pointed. What’s also visible in this shot, and in some others on this page, is that the bird’s feet are black only for about half of their length. (See large size.)
Putting it all together, then, I believe that if I’m interpreting the images correctly, the combination of pointed central rectrices, barred greater under primary coverts, a smaller head and finer bill, and half-black feet all point toward an ID of Parasitic Jaeger. Parasitic Jaeger is on the Louisiana Bird Record Committee’s review list. Below are some additional images, and I welcome comments, questions, and alternative or supporting interpretations.
Showing small cinnamon tips on scapulars and greater coverts on the upperwing. © Justin Bosler
Another look at the upper surface of the wings. © Dave Patton
© Dave Patton
Central rectrices look pointed in this shot by Erik Johnson. I think this supports the sharper image by Justin Bosler above; this image alone might be a tough sell.
Harassing a Bridled Tern (Onychoprion anaethetus). © Erik Johnson
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