I want to echo Mike Tove's observations on his cruise to Antarctica. I did the cruise on the same ship but a different route a year ago. Last year, it departed Santiago, Chile and ended in Buenos Aries after Antarctica and the Falklands, giving three at sea days on both the Pacific and Atlantic sides of southern South America. The current cruise route begins and ends in Buenos Aries missing most of the Pacific which has several seabirds not on the Atlantic side It would be great if Princess went back to the old route but the current one is still an excellent way to see a lot of seabirds.
I had 13 species of albatross, 30 other tubenoses (petrels, storm-petrels, shearwaters, diving-petrels, etc) including Snow and Antarctic Petrel and seven species of penguin. The only miss I had in Antarctica was a long shot chance for a stray Emperor Penguin. I have a public ebird trip report for the entire trip if you are interested. The cruise ship is so stable you can use a scope and the Sapphire Princess has a deck on the bow low enough for great viewing.
One thing Mike did not mention is day long port calls allowing birding of sites in Argentina and Chile and the Falkland Islands. While you do not make landings in zodiacs on a big cruise ship in Antarctica, you can walk with the King, Magellanic, and Gentoo Penguins in your day on the Falklands if you want while looking at the endemic flightless Steamer Duck.
