aldelie penguins spend their (austral) winters in the seas surrounding the antarctic pack ice - about 4,000km from their southern spring breeding grounds - where they fatten on krill. the krill feed on phytoplankton beneath the icebergs, but warming waters due to climate change has reduced their numbers by up to 80 percent as the plankton, which are now unable to access cold water nutrients, are dying off.
adelies are the most southern living penguin, but head north as the summer ends to escape the protracted darkness of the winter. a warming climate, however, has meant a reduced northern icepack, and has seen the encroachment of other penguins onto their southern summer territory who previously found it too cold. the adelie population northeast of the ross sea, for example, has declined by 90 percent.
as one adelie expert put it, these penguins face possible extinction not merely by a loss of habitat, but by an unshakable fear of darkness; adelies need light, if only twilight, to forage and navigate, and as comfort against predators. but as they are pushed further south they may ultimately find themselves trapped behind a curtain of polar night for which they have no hardwired strategy.