Thirty years ago, two young biologists named Robert MacArthur and Edward O. Wilson triggered a far-reaching scientific revolution. In a book titled The Theory of Island Biogeography, they presented a new view of a little-understood matter: the geographical patterns in which animal and plant species occur. Why do marsupials exist in Australia and South America, but not in Africa? Why do tigers exist in Asia, but not in New Guinea?

Influenced by MacArthur and Wilson's book, an entire generation of ecologists has recognized that island biogeography - the study of the distribution of species on islands and islandlike patches of landscape - yields important insights into the origin and extinction of species everywhere.

The new mode of thought focuses particularly on a single question: Why have island ecosystems always suffered such high rates of extinction? In our own age, with all the world's landscapes, from Tasmania to the Amazon to Yellowstone, now being carved into islandlike fragments by human activity, the implications of island biogeography are more urgent than ever.

Until now, this scientific revolution has remained unknown to the general public. But over the past eight years, David Quammen has followed its threads on a globe-circling journey of discovery. In Madagascar, he has considered the meaning of tenrecs, a group of strange, prickly mammals native to that island. On the island of Guam, he has confronted a pestilential explosion of snakes and spiders.

In these and other places, he has prowled through wild terrain with extraordinary scientists who study unusual beasts. The result is The Song of the Dodo, a book filled with landscape, wonder, and ideas. Besides being a grand outdoor adventure, it is, above all, a wake-up call to the age of extinctions.