Penguins' struggle is a warning to world

Adelies are being stalked by a threat they cannot see and cannot fight off: the weather. The birds, which have adapted over millions of years to the most extreme climate on Earth, are beginning to die off by the tens of thousands as a result of global warming.

The Adelie penguin is regarded as an "indicator" species, an animal so delicately attuned to its environment that its survival is threatened as soon as something goes wrong. So as temperatures rise, Adelies are among the first to feel the effects, early victims of the devastating worldwide changes that scientists expect if the warming persists and intensifies.