The kea, a crow-sized parrot that lives in the rugged mountains of New Zealand, is considered by some a playful comic and by others a vicious killer. Its true character is a mystery that biologists have debated for more than a century. Judy Diamond and Alan Bond have written a comprehensive account of the kea's contradictory nature, and their conclusions cast new light on the origins of behavioral flexibility and the problem of species survival in human environments everywhere.

New Zealand's geological remoteness has made the country home to a bizarre assemblage of plants and animals that...