Penguins and other seabirds in Antarctica have shown dramatic responses to
changes in sea-ice extent over the past century (Ainley et al. 2003, Croxall et al. 2002,
Smith et al. 1999). The sea-ice dependent Ad´elie and emperor penguins (Pygoscelis
adeliae and Aptenodytes forsteri, respectively) have nearly disappeared from their northernmost
sites around Antarctica since 1970. Emperors have declined from 300 breeding
pairs down to just 9 in the western Antarctic Peninsula (Gross 2005), with less
severe declines atTerre Ad´elie (66◦ S), where they are now at 50% of pre-1970s abundances
(Barbraud & Weimerskirch 2001). Ad´elies have declined by 70% on Anvers
Island (64◦–65◦ S along the Antarctic peninsula (Emslie et al. 1998, Fraser et al. 1992),
whereas they are thriving at the more-southerly Ross Island at 77◦ S (Wilson et al.
2001)—effectively shifting this species poleward. In the long-term, sea-ice-dependent
birds will suffer a general reduction of habitat as ice shelves contract [e.g., as has already
occured in the Ross Sea (IPCC 2001b)] or collapse [e.g., as did the Larsen Ice
Shelves along the Antarctic Peninsula in 2002 (Alley et al. 2005)].
In contrast, open-ocean feeding penguins—the chinstrap and gentoo—invaded
southward along the Antarctic Peninsula between 20 and 50 years ago, with paleological
evidence that gentoo had been absent from the Palmer region for 800 years
previously (Emslie et al. 1998, Fraser et al. 1992). Plants have also benefited from
warming conditions. Two Antarctic vascular plants (a grass, Deschampsia antarctica,
and a cushion plant, Colobanthus quitensis) have increased in abundance and begun to
colonize novel areas over a 27-year period (Smith 1994).