In 1598 Dutch sailors bound for the rich spice islands of the Far East began making stops at an obscure Indian Ocean island named Mauritius. Along with fresh water, they found that the island provided another resource highly prized by sailors, who often got by for months on little more than salt pork and hardtack: fresh meat. The island harbored a dorky, 30-pound bird that was too ungainly to fly and too stupid to run away from men with clubs.

Perhaps it had an unmusical, repetitive song, or perhaps the name they gave the unlikely bird derived from Dutch words for “sluggard” or “round ass.” No one really knows. What is known is that within the span of a human lifetime the bird they found, the bird they called the dodo, was wiped off the face of the earth. As David Quammen puts it in his new book, The Song of the Dodo, once the sailors began stopping at its island home “the toilet of its destiny had been flushed.”

The dodo has had a livelier afterlife than most extinct species, as a symbol of trusting stupidity and as a poster child for extinction. It was, according to one modern-day Mauritian ecologist, “the first time in the whole of man’s history that he actually realized he had caused the disappearance of a species.”

It’s poignant then to read that the story of the dodo is being repeated time and again around the world. Quammen, a former columnist for Outside magazine, is as good as any writer at communicating complex scientific ideas in language that’s easily grasped, even compelling. He’s able to make 702 pages not just a hell of a lot of science, but an eloquent, readable, occasionally irreverent tale that’s hard to put down.

Though Quammen’s writing can be humorous, The Song of the Dodo is a sobering look at the possible future of much of the plant and animal life around us. In part it’s also a travel book in which Quammen visits Mauritius, Tasmania, Madagascar, the Galapagos, Guam, and other places that support remarkably large numbers of rare and endangered creatures. He comes across as a rather shy, bookish fellow who feels the same trepidation most of us would about blundering into huge spiderwebs in a tropical forest, scaling a steep cliff looking for the nest of a rare bird, or eating the food at street stalls in Indonesia. But these entertaining adventures are not what makes the book a good read. Rather, it’s the exploration of the ideas summarized in the book’s subtitle, Island Biogeography in an Age of Extinctions: Why have so many species gone extinct on islands? And what does that bode for the future of the mainlands most of us live on?

Quammen’s traveling companions on his journey by boat, plane, and computerized library catalog are numerous biologists and conservationists as well as the theorists who’ve developed the concepts of island ecology, from Charles Darwin on down. It turns out that much of the modern science of ecology is based on observations made on islands, of which Darwin’s work in the Galapagos is the most famous (though it wasn’t quite as pathbreaking as we were taught in high school). That’s not because islands are nice places to go, but because they, with their relatively simple ecological systems, are easier to understand than mainlands. It’s like trying to understand the genealogy of a small farm town as opposed to that of Chicago–the stories are just as interesting, and there are fewer strands to follow, fewer interactions to look at.

The ecological theorems Quammen’s characters have developed over the last century and a half include these: The smaller the island, the fewer species it supports. The smaller the population of a given species, the likelier it is to die out as a result of famine, disease, storms, the introduction of a new predator, or other perturbations in its environment. An island far from a mainland will have a lower rate of species immigration than one near a mainland, and these remote islands generally support fewer species than those near the mainland.

Small islands, logically enough, tend to have a preponderance of small populations. The fauna and flora of many islands also evolved in isolation from the more intense competition that tends to occur on continental mainlands. For these reasons islands have suffered the brunt of extinctions in the last few hundred years. Of the 171 species and subspecies of birds that have vanished in the last four centuries, 155 were exclusively island creatures. Hawaii alone lost 24 and now has several species that are barely hanging on. Island species are 50 times more likely to go extinct than mainland species, and those that dwell on small islands are at greatest risk.

In the case of the dodo, all it took was a few humans hunting the animals for meat and the pigs and monkeys the sailors introduced to the island, which ate the birds’ eggs. But Homo sapiens, among the most adaptable of creatures, has not been immune to these ecological laws. Take the population of medieval Iceland, which was colonized around the turn of the millennium by hardy Vikings. The Icelanders were so isolated in the middle of the Atlantic Ocean that when ships arrived from mainland Europe every few decades or centuries they tended to drop dead in droves, victims of shipboard diseases such as smallpox, to which mainlanders had acquired some immunity. (One hopes the Icelanders were able to enjoy the news and goods the sailors brought before they fell sick.) The Tasmanian aborigines, of whom Quammen makes a case study, are another good example of a separate population that was all but wiped out by competition with more aggressive newcomers.

One of the centerpieces of The Song of the Dodo is a little book called The Theory of Island Biogeography, by Robert MacArthur and Edward O. Wilson. Published in 1967, it revolutionized ecology with its assertion that island ecology is pertinent to the ecology of mainlands too. A woodlot on a prairie is an island, as are a meadow in a forest and a marsh in a desert. All are surrounded by alien terrain hostile to some of the island’s inhabitants.

By the late 1960s biologists knew that large habitats all around the world–the Amazon rainforest, the Great Plains, the Everglades, midwestern marshes and forests, whatever–were being sliced and diced into smaller and smaller pieces. What made The Theory of Island Biogeography revolutionary was its claim that this fragmentation–the creation of islands–would result in an increased rate of extinctions.

That claim turned numerous mild-mannered scientists into radicals, who quickly found themselves embroiled in political fights to save the creatures they would have preferred to study in peace. Now they find themselves facing the pressures of a world from which more than 1,100 species of plants and animals have vanished in the last 400 years. According to the Nature Conservancy, about a third of the species in North America have populations small enough to justify worrying about their future survival. These are primarily species of the mainland, not of islands–at least not islands surrounded by water.

To see how all this applies to Illinois, consider what the place once looked like. Louis Joliet, the Frenchman who in 1673 traversed the Mississippi and Illinois rivers, wrote, “There are prairies three, six, ten, and twenty leagues in length and three in width, surrounded by forests of the same extent. [A league is about three miles.] Beyond these, the prairies begin again, so that there is as much of one sort of land as of the other.”

In the two centuries after Joliet’s visit, European or American visitors to Illinois, accustomed to heavily wooded landscapes, recorded varying responses to the enormity of the prairies. Some found a paradisial garden, others a bleak wasteland. (Those who had to make a living from it–who probably viewed it as something between these two extremes–were less inclined to leave a written record than travelers who had the luxury of reflection and the time and inclination to write.)

But whether travelers viewed the landscape positively or negatively, few could resist commenting on its scale. Take the report of Scotsman Patrick Shirreff, who in 1833 rode southwest from the new village of Chicago: “Perhaps conceptions of beauty and grouping of trees, formed in the artificial school of Britain, are inapplicable to the magnificent scale on which nature hath adorned the country between Chicago and Springfield. The works of man are mere distortions compared with those of nature, and I have no doubt many prairies, containing hundreds of square miles, exceed the finest English parks in beauty as much as they do in extent. Sometimes I found myself in the midst of the area without a tree or object of any kind within the range of vision, the surface, clothed with interesting vegetation around me, appearing like a sea, suggested ideas which I had not then the means of recording, and cannot be recalled.”

Presettlement Illinois had both prairies and forests; more important, it had big forests and big prairies. Both vanished swiftly once settlers began hacking openings in the forests for crops and pastures, and planting woodlots on the prairies for windbreaks, firewood, and timber. The settlers turned big patches into little patches. They converted a landscape of big islands into a place of little islands.

Today grasslands and forests measured in leagues can scarcely be found in Illinois. There are plenty of trees, and there is plenty of grass (especially if you count corn and Kentucky bluegrass as modern versions of big bluestem), but the structure of the landscape is entirely different. Illinois today bears about as much resemblance to the landscape Joliet saw as a loaf of sliced white bread does to a crunchy baguette.

The ecological rules Quammen enunciates in The Song of the Dodo hold true in archipelagoes of grassland fragments or forest fragments. The species that require large tracts of one or the other sort of land–bison, elk, black bears, cougars–are gone from Illinois. And many others, less charismatic, are in trouble. Grassland birds like the greater prairie chicken, upland sandpiper, and short-eared owl require extensive areas without trees (in which great horned owls and other predators can hide). These species have become rare in Illinois.

The same is true in forests. Wood thrushes, warblers, tanagers, vireos, and many other forest species have been in decline throughout much of the eastern and central U.S. in the last few decades. These are species that winter in the tropics, but recent research seems to indicate that tropical deforestation isn’t having as much of an impact on their numbers as changes in their temperate breeding grounds. The biggest culprit is forest fragmentation. When forests are cut into smaller pieces predators that thrive along edges–raccoons, crows, blue jays, all of which devour birds’ eggs–expand their ranges.

Cowbirds like edges too. Cowbirds don’t build nests of their own; they lay their eggs in the nests of other birds. Their eggs tend to hatch quickly, and their chicks are aggressive, so the foster parents often end up raising baby cowbirds rather than their own baby thrushes or warblers. Cowbirds are an open-country species, but with the opening of forest habitat they can find the nests of many forest species that didn’t evolve in conjunction with cowbirds.

Research by Scott Robinson of the Illinois Natural History Survey in southern Illinois’ Shawnee National Forest has shown that even when a wood-thrush nest is more than 300 meters from the edge of a large forest patch its chance of being discovered and parasitized by cowbirds is over 90 percent. The islands of forest there–among the largest left in the state–are growing too small for wood thrushes. The species presumably survives in the area only because surplus birds raised in other larger forest areas spill over into the Shawnee. If those other islands suffer the same fate the wood thrush’s sweet, ethereal song may become as scarce in Illinois as that of the dodo.

Quammen doesn’t offer a lot of solutions to the extinction crisis, with its potential for a future of what he terms “soul-withering biological loneliness,” in which human beings will be surrounded only by pigeons, rats, dandelions, and other adaptable species rather than tigers, elephants, and lady’s slippers. He does profile some activist biologists who’ve done yeomen’s work in pulling some species back from the brink. The Mauritius kestrel, a falcon of the very forests in which the dodo’s unrecorded song could once be heard, was down to a population of four birds before it recovered with the help of a captive-breeding program.

But the main problems Quammen elaborates can’t be solved by the pluck of a few scientists. An ever-increasing human population may well be too preoccupied with its own survival in coming decades to worry much about dodos or prairie chickens or wood thrushes. Another problem is that most of us prefer edges. Those early settlers on the Illinois prairie weren’t planting trees only for firewood and timber; it was comforting to have some trees in the sea of grass. Human beings tend to like places with transitions; the most expensive real estate is always that on the water or on a park with grass and trees. Working against that tendency–for instance, leaving some big habitats in one piece for Mauritius kestrels or wood thrushes–is going to take a more concerted expression of love for the natural world than we’ve so far been able to muster.

The Song of the Dodo: Island Biogeography in an Age of Extinctions by David Quammen, Scribner, $32.50.

Art accompanying story in printed newspaper (not available in this archive): illustration/Ralph Creasman.