Pomarine Jaeger, Stercorarius pomarinus
Jaegers can be hard to identify, but one sure mark is the central tail feather extension of the adult. The Pomarine has two long feathers which form a twisted spoon-shaped extension, see above and below. Compare the very long thin double streamers of the Long-tailed, and the shorter triangular extension of the Parasitic.
The long central tail feathers are often lost by adult Pomarines soon after they leave their breeding grounds in the Arctic, as in the breeding plumage bird above. In that case, other and less clearcut characteristics have to be used. The Pomarine is the largest of the three jaeger species, has the stockiest build, proportionately the largest bill, the slowest and most powerful-looking wing motion in flight, and on average the most white feather shafts showing on the upper wing surface -- eight in the bird at the top of the page, five visible in the next one down. (Long-tailed ranges 2-3, Parasitic 3-5, compared to 5-8 in Pomarine.)
The bird above is an adult still mostly in breeding plumage, though the central tail "spoon"
is gone; note the clear demarcation of dark cap, light yellow rest of head, brown breast
band, solid white below, and solid brown underwing. The bird below, with solid brown
underwing coverts and heavy barring on the throat and belly, is an adult in non-breeding
plumage; note the six visible white shafts on the upper side of its flight feathers.
This bird is an immature; it resembles the non-breeding adult shown next above, but has barred rather than solid brown underwing coverts.