Book excerpt: When sea-ice declines, so does the population of Adelie penguins, making this species a predictive indicator of the effects of global warming. This book summarizes our present ecological knowledge of this species: its biology, behavior, and ecology within the Antarctic ecosystem; the ecological factors important to its life history; and details of the mechanisms by which it is responding to climate change. The narrative is complemented by richly written texts from the earliest Antarctic naturalists, fine illustrations from the accomplished artist Lucia deLeiris, and photographs by the author.