There are no real birds of prey on Antarctica (nor on most of the subantarctic islands), but the skuas happily take this place. They are more gull-like, with a dark brown plumage and without the hooked bill and claws of the raptors, but they do like a penguin egg or chick. Or any other bird for that matter.
There are several species and subspecies one can see on an Antarctic trip, making identification sometimes (actually often) difficult. In southern Patagonia, it starts with the Chilean Skua. Further south one can see the South Polar Skua or one of the different subspecies of the Brown Skua, or maybe even a hybrid between the last two species. On the Falklands, it’s easy, with only the local subspecies of the Brown Skua (aptly named Falkland (Brown) Skua) and on South Georgia, one can only see the Subantarctic (Brown) Skua.
But on the Peninsula, the fun starts with the combination of the Subantarctic (Brown) Skua and the South Polar Skua. Differences are small with the Subantarctic Skua having a bit a heavier bill and larger head and having a bit more streaked plumage compared to the South Polar Skua. But as both species are quite variable and the South Polar Skua having different colour morphs, it’s often challenging to come to a specific identification.
When one gets further south on Antarctica, it gets easy again. Here there are no Subantarctic Brown Skuas anymore, so all skuas you see are South Polar Skuas. During my trips in the Ross’ Sea, we only saw light morph South Polar Skuas, which made life for a guide a lot easier.