DURING THE SECOND WORLD WAR, Japan and the United States fought over Alaska’s Aleutian Islands. The United States Navy drove out Japan, and the Aleutian campaign was almost forgotten — except by biologists. Sometime during the fray, according to William Stolzenburg, “a rat or two secretly accompanied the soldiers ashore to Kiska,” a volcanic island that is one of the bigger landmasses in the western Aleutians. Within a few decades, the rats somehow managed to cross the frigid, treeless land to the other side of Kiska, where they found a prize: a huge colony of least auklets, three-ounce seabirds. For the rats, the nearly helpless newborn auks were a living sea of breakfast. The rats’ numbers exploded as they ate their way through the colony.

Kiska is by no means unique, according to Rat Island: Predators in Paradise and the World’s Greatest Wildlife Rescue, Stolzenburg’s account of the “biological SWAT teams” who are trying to undo the ecological damage wreaked by introduced species on islands. Islands account for less than 5 percent of the world’s surface area but have been the scene of about three quarters of known extinctions since 1600. Many or most of these lost species are birds, and many or most of these lost birds have fallen to the depredation of exotic mammals — creatures imported, often inadvertently, by human beings. Rats are especially noteworthy culprits; Stolzenburg’s book is chockablock with riveting, gruesome descriptions of rats gnawing holes in the skulls of rare avifauna. Rat Island could be described, not entirely unfairly, as the story of a crusade to kill common species in uncommon places.

Massacring rats turns out to be more difficult and interesting than one would think. The species has spent millennia avoiding human predators. Even small islands offer countless hiding places. Eliminating rats from such places inevitably becomes an expensive, quasi-military enterprise. Helicopter assaults transpire more than once in this book. Unsurprisingly, the humans involved are eccentric and passionate. They are also increasingly effective. Since the 1980s, Rat Island says, people have wiped out invasive predators on more than eight hundred islands around the world. In most of those places, native bird populations have rebounded.

Stolzenburg clearly regards these eradications as a good thing. From the evidence in his book, it’s hard to disagree; in these delicate places, even such innocuous species as cats, pigs, and foxes can ravage entire ecosystems. Yet he also does much huffing about the opposition to them. Stolzenburg paints some of the critics as loony, and he may be right. But he never seems to have actually talked to them — a basic journalistic responsibility.

This is a pity; the animal-rights activists who are fighting eradication may be muddle-headed, but they are pointing to a real conundrum: how do humans choose which creatures are more worthy of survival? Most people like rats much less than they like the Xantus’s murrelet those rats were extinguishing in the Channel Islands. But few people would so readily slaughter cats or stoats. Is simple dislike enough to wipe out an entire population? What is the yardstick?

Moreover, as Stolzenburg admits, the consequences of flooding an island with rat poison are hard to predict — witness the bald eagles killed in Aleutian efforts. And the expenses are enormous. Are multimillion-dollar rat pogroms on remote islets the best way to use limited conservation budgets? The answer may be yes, but Stolzenburg would have written a better book if he fairly asked the question. His wildlife defenders are brave and skillfully evoked, but playing God is more complicated than he allows.