The Antarctic Skua (Catharacta antarctica):

Shown here, this oversized relative of the sea gull spends its austral summers in Antarctica and flies north for the rest of the year. A typical clutch size for a skua consists of two eggs in a nest built from rocks, with an average survivability of 50%. They are extremely territorial birds and excellent scavengers, feeding primarily on Adelie penguin eggs and in McMurdo, sandwiches and cookies from the galley. The New Zealand Maori word for skua is Hakoakoa.

I saw my first skua last week while skiing out to the runway and since then there has been one recorded attack involving an unsuspecting first-year and a roast beef sandwich.

~G

References:

Bird Life International (2004)

Wikipdia (2006)