Biological diversity must be viewed as a global resource, like the atmosphere or the oceans. New uses for it are being discovered that can relieve both human suffering and environmental destruction. Only a tiny fraction of species with potential economic importance have been utilized; 20 species supply 90 per cent of the world's food, and just three (wheat, maize, and rice) provide more than half. In most parts of the world, these few crops are grown in monocultures that are particularly sensitive to insect attacks and disease. Yet tens of thousands of edible species—many possibly superior to those already in use—remain unexploited. The rapid development of biotechnology will speed up the use of available genetic resources, thereby increasing the value of maintaining the most diverse possible pool of species and genes.

Rapid destruction of the natural environment is quickly reducing both the number of species and the amount of genetic variation within individual species. Perhaps a quarter of the earth's total biological diversity, amounting to about a million species, is in serious risk of extinction during the next 20 to 30 years. This is perhaps 1,000 times faster than the historical rate of extinction. If a forest is reduced to 10 per cent of its original size, the estimated number of species that can continue to exist in it will decline eventually by half. Habitat reduction on this scale has already occurred in many parts of the tropics in recent decades. More than half of the world's species are believed to live in tropical rain forests. They were disappearing at a rate of more than 7 million hectares per year in the early 1980s; this implies a 40 per cent reduction in their total area from the mid-1980s to 2000. Other species-rich habitats in danger include tropical coral reefs, geologically ancient lakes, and coastal wetlands.

In the year 2000, Spix's macaws vanished from northeast Brazil. The large, powder-blue birds' disappearance was no fluke. Farmers and timber cutters cleared their wooded river forest habitat. Bird traders bagged the birds, and hunters shot them. Today, only 40-60 Spix's macaws still live in aviaries, where most of them were born. None remain in riverside woodlands where the birds were "discovered" just 183 years ago.

While scientists puzzle over the prospects for breeding these birds and releasing their progeny back to the wild, many wonder how re- introduced birds would learn to locate food. With little habitat left, they would need to fly to other scattered habitat "islands" to find enough fruit and seeds to survive. Even if all of this worked out, the birds' young would be threatened by an invasive introduced insect—the "Africanized" hybrid honeybee—that inhabits 40 percent of remaining tree cavities suitable for macaw nesting.

The demise of the Spix's macaw resonates far beyond one tiny Brazilian region, for this is far from an isolated incident. According to a 2000 study published by the global conservation organization BirdLife International, the Spix's macaw and almost 1,200 additional species—about 12 percent of the world's remaining bird species—may face extinction within the next century. Most struggle against a deadly mixture of threats. Although some bird extinctions now seem imminent, many can still be avoided with a deep commitment to bird conservation as an integral part of a sustainable development strategy.

By the end of the 1980s, at least 14 Australian amphibian species had gone into serious decline or disappeared entirely from the eastern mountainous regions of the continent. The southern dayfrog and the gastric breeding frog, which was only discovered in 1973,  commonly been found in the same areas have not been seen in the wild since 1981. Three other species in southeastern Queensland have declined by more than 90 percent. Further north, in the tropical forests two species declined sharply in 1985; one of them has not been seen since. And in the tropical rain forests of northern Queensland, large- scale declines began in 1989—seven species dipped sharply; four can no longer be found in the wild. All these species were locally endemic: they did not exist anywhere else in the world.

Several -hypotheses about Australian amphibian declines have been proposed, but there are no widely accepted, definitive answers. And the mystery spreads beyond Australia. By the end of the 1980s, reports of declines and disappearances emerged from most other regions of the world where amphibians were reasonably well monitored—in North America, parts of South America, and Europe. In Costa Rica's Monteverde National Park, populations of 20 of the 50 native amphibian species, including the famous Golden Toad,  have declined or disappeared since 1987. And in California's Sierra Nevada, five out of seven native amphibians have disappeared or declined sharply since the early 1900s.

There were some uncanny global similarities, to these declines and extinctions— patterns that suggested something more ominous could be taking place. The declines were, in the first place, very rapid. They sometimes involved whole assemblages of species, rather than just one or two. And they were occurring not just in areas that were obviously disturbed, but in some of the world's most carefully protected parks, such as Costa Rica's Monteverde Cloud Forest Reserve and Yosemite National Park in the western United States. These were not the kinds of losses that could be readily predicted—or explained. Something peculiar was happening to Amphibia.  Habitat loss, and pollution are clearly major factors in the decline of populations of amphibians.  But other, more subtle factors are at work, such as increased UV radiation, the introduction of non-native predators and reduced resistance to fungal and bacterial disease..

Spinl's Macaw and the Mount Verde Golden Toad are case studies of unsustainablility, touching on all the major environmental issues of our day.