[clydebirder]

Originally Posted by phil baber

A more extensive reply, which i think is needed.
On Pom the dark cap extends below the gape line. This can be seen well on this bird. On Arctic it stops at the gape line.
Pom has a much more well-defined breast band. An appreciably darker ventral area. A fuller bellied heavier appearance.
As the bird in this photo demonstrates, it is like an Arctic on steroids. Between Common and Herring Gull in size.
The light blue dark tipped bill is obvious in these photos. This is more pronounced on Pom than Arctic, and can be apparent at ranges up to 300M as a distinct feature.
Don't let the lack of "spoons" fool you.
These are great photos of an post-breeding adult Pomarine Skua!

This bird doesn't have an appreciably darker ventral area, that's straight out of a book

I've attached a post breeding plumaged Pomarine, note the extent of the dark area at the vent (and most adults are darker than this) and compare it to original images, also note the bull necked and full chested look typical of Pomarine.
I've also attached an Arctic Skua image of a bird similar to the bird in the original images.

cheers, John