Evolution on a frozen continent

Ancient-DNA studies of Adélie penguins combined with a detailed picture of a remarkable continent's geological past explain how evolution took place. In Antarctica, the Pleistocene epoch was distinguished by the repeated expansion and collapse of huge marine-based ice sheets as well as by fluctuations in the volume of ice on the Antarctic landmass. Adélie penguins are the dominant terrestrial species in Antarctica. Adélies breed in colonies at ice-free sites around the coast of Antarctica and on some islands off the Aritarctic coastline. Adélie penguins begin a regular annual cycle of breeding during the Antarctic spring, with males typically arriving at Ross Island colony sites in the last week of October and early November, on average four days earlier than females. Abandoned penguin nesting sites in areas where Adélies do not currently nest have been recognized as relict colonies and are common landscape features along the Antarctic coasts.