I have seen a lot of Great Skuas and this bird looks wrong in colour (no gingery tones) and pattern (rather uniform, not "speckled"). I have very limited experience of "Subantarctics" Skua (= Brown?, can't remember the status of the taxonomic shenanigans with these offhand); however, the ones I've seen were dark chocolate colour without the head/body vs. wings/mantle contrast evident for this bird."  and

"Looked at a few field guides for Africa, Australia, Indian subcontient that include southern ocean seabirds last night All three include both "Brown" (under various names with it lumped as "Great" in the Aus book, but with lonbergi, one of the southern races, clearly meant) and South Polar Skuas, with Great "proper" also included in the Africa book. All agree that contrast between paler head/body and dark wings is something distinguishing South Polar Skua from Brown. Pale greyish feathering at the base of the bill is also referred to in one of the books. This seems to be visible in Chuck Saleeby's flight shots and Dan's perched shot.

Ian Sinclair's African book suggests that S P Skua sits higher in the water than other Skuas. Haven't had a chance to compare photos on the internet to see if this is at all useful. His book also refers to differences in build, with S P being suggested to be more lightly built, specifically more Pomarine Jaeger-like, than other Skuas. In the field this was not apparent to me, but then any Skua in isolation looks pretty massive. From the pictures I can convince myself it's less bulky than a Great (and therefore also presumably less so than a Brown)."

Earl Horn's comments:  "With my limited experience I believe it is a South Polar Skua based on the hooded effect of the head, the lighter coloration of the nape and neck, and the strong contrast of the lighter under parts compared to the darker upperparts.

The head looked to be almost a golden brown, a little darker than the nape and neck, with a dark blotch behind the eye. The bill looked to be all one color and ranged from black to gray depending on how the sun hit it.

The back and upper wings were dark brown with the strong white flash of the primary wing coverts and white primary shafts. There was some slight mottling on the back. The under wing had a contrasting pattern of dark lesser and median coverts with lighter greater coverts and flight feathers, with a strong white flash of the primaries extending beyond the coverts. The darker coverts also were in strong contrast to the under parts of the body which looked uniformly pale light brown/tan from the neck through the belly with the undertail coverts a little darker. I saw no barring in the undertail and the tail was dark, short and rounded.

Here's my thinking on eliminating other close species:

I don't think it is any of the three jaegers based on the apparent greater size and chunkiness of this bird. There were no birds with it for a direct comparison, however there were plenty of crows of both species flying around and it was obvious that this bird was much bigger than them. The white flash on the upper wing was more extensive than on the jaegers and there was no barring on the upper or under tail coverts. I could be wrong but the dark adult Pomarine Jaeger is the only one that has a plumage without any barring in the undertail, but besides the obvious lack of extended tail feathers in an adult it is also fairly uniformly dark brown everywhere unlike this bird.

Chilean Skua I would eliminate based on the coloration of the under parts which are reddish brown in the body and under wing coverts. It also has a cap rather than a hooded look and a bi-colored bill.

Great Skua I would also eliminate on coloration. It also should be more red brown darker overall and should have a lot of mottling on the upper body with the head having a capped appearance. In lighter worn versions the mottling would be even greater.

Brown/Antarctic Skua I would eliminate based on the lack of or minimal contrast of the darker upper parts with the just slightly lighter under parts. This skua is also much darker overall than the South Polar Skua.

I know there are a lot of variations in the various skuas and I have made this elimination seem simpler than it really is, but I tried to cover some of the main points that I have been able to glean from the various books I have which include:

The Sibley Guide to Birds; David Sibley

Skuas and Jaegers; Olsen and Larsen

Seabirds of the World, A photographic Guide; Harrison Seabirds of the World, An Identification Guide; Harrison"

The lighter brownish gray coloration on the nape, down the sides of neck and in front of shoulder gives a "saddle" area contrasting with the darker back. The back of the head has a light barring pattern. No indication of a crown cap. The bill is dark, the top of the upper mandible appears lighter. There is a small white area at the base of the upper mandible."