For millions of years the Adélie penguins have thrived within the natural ebb and flow of temperatures on the Antarctic continent. During colder periods, when glaciers would expand to cover the penguins' preferred rocky breeding grounds, the species' colonies would relocate. During warmer periods when glacier ice would melt, revealing the rocky earth, the penguin colonies would return to old nesting areas. But this way of life may no longer be sustainable for these penguins, according to a study published Wednesday in the journal Scientific Reports. "It is only in recent decades that we know Adélie penguin population declines are associated with warming, which suggests that many regions of Antarctica have warmed too much and that further warming is no longer positive for the species," lead author Megan Cimino, who earned her doctoral degree at the University of Delaware in May and is now a postdoctoral scholar at Scripps Institution of Oceanography, UC San Diego, said in a press release.