The plight of birds: today, more than a thousand species of birds face extinction. Many more are in steady decline. Significantly, the strategies that can stop this attrition are the same strategies needed to achieve a sustainable human future.

• Author: Youth, Howard
• Position: Donana National Park

Very little remains of the rich wildlife that once flourished in Europe. Most of the wolves, bears, and bison are long gone. The few fragments of wilderness that remain are highly valued. Among them, not many can compare with Spain's Donana National Park, which lies on the Mediterranean coast a short distance across from Africa, and which is habitat to animals from two continents--and to an extraordinary variety of birds. Donana's 50,000 hectares (123,000 acres) of marsh, dune, brush, and forest are one of the largest remaining breeding grounds for the endangered Spanish imperial eagle (Aquila adalberti) and the wintering grounds of hundreds of thousands of waterfowl.

Yet, Donana is a paradise in peril. Siltation from upriver and water demands from irrigated farms surrounding the park are drying out marshes earlier in the year than in decades past. Nesting waterfowl such as the once abundant and now rare marbled duck (Marmaronetta angustirostris) are left high and dry. Cut off from the water, the birds have poor prospects for finding food and few places to escape foxes and other predators. Nonnative eucalyptus trees, which were planted before the area was declared a park in 1969, have been growing fast and choking out native vegetation. And in 1998, a zinc mine reservoir just north of the park burst and spilled 5 million cubic meters of acidic water--heavily laced with cadmium, lead, copper, and other heavy metals--into the river.

The spill covered almost 10,000 hecrares (25,000 acres) with toxic sludge, saturating the park's buffer zone and killing thousands of fish and birds, leaving much of the surviving wildlife contaminated at levels that likely impair their ability to breed.

Threats to Donana's birdlife exemplify the range of pressures on many of the world's birds, which are increasingly in jeopardy despite their ability to fly from one place to another. From the nearly 3-metertall African ostrich to Cuba's 6-centimeter-long bee hummingbird, more than 9,800 bird species live on the planet. They perform essential natural services, without which our own existence would be greatly compromised. Birds pollinate crops, disperse seeds, control insects and rodents, and clean up carrion. For those of us who pay more attention, the colors, songs, flight, and varied behaviors of birds provide great inspiration. Yet, millions of us may be aware of birds' presence only on the margins of our consciousness. As a result, many bird species appear likely to die off in the coming decades.

Unprecedented Decline

Like Donana's wildfowl, most of the world's declining bird species face multiple threats, virtually all of them from human activities. Even when a species is endangered by a single threat, remediation is difficult; but when the dangers come from several directions, the difficulty grows exponentially. The ostrich (Struthio camelus), for example, is being decimated both by hunting and by habitat loss, especially in the northern and western part of its wide but increasingly fragmented range in Africa. The world's largest bird, it lays the world's largest egg. But neither bird nor egg is any match for human hunters.

"They're getting it from both sides. Adults are being killed and the eggs are Black harrier being robbed," says Smithsonian Institution scientist Steve Monfort. In 2001, Monfort participated in a wildlife survey in Chad, and found no ostriches--only years-old shattered egg fragments. And in most parts of Africa where scattered ostriches do remain to take their chances with hunters, the fragile grasslands on which they depend for their varied diet of leaves, seeds, roots, and insects are being chewed up by over-grazing of livestock.

Variants of this story are being repeated on every continent, including Antarctica. In North America, massive displacement of native grasslands for mono-culture farming and grazing is driving out two species of prairie chickens (Tympanuchus phasianellus and Tympanuchus pallidicinctus). In Eurasia, the great bustard (Otis tarda) and three other species of bustard are in rapid decline--there, too, as a result of what ecologist Paul Goriup calls the "generally low priority afforded to the conservation and sustainable use of grasslands, steppes, and rangelands throughout the world." In France and Spain, the pin-tailed sandgrouse (Pterocles alchata) is in biological freefall, for similar reasons. As the human population expands (from 1.6 billion to more than 6 billion in the past century alone), the Earth itself is becoming increasingly humanized--meaning that landscapes are being deforested, drained, paved, and chemically altered to make way for Homo sapiens. Generally, the more human-dominated a landscape is, t he more biologically poor and unstable it becomes overall.

Over the past two centuries, 103 species of birds have gone extinct. Among those never to be seen again are the New Zealand laughing owl (Sceloglaux albifacies), the Cuban macaw (Ara tricolor), and the once spectacularly abundant North American passenger pigeon (Ectopistes migratorius). In the next one century 1,186 species could go extinct, according to Threatened Birds of the World, a comprehensive study published in 2000 by the global conservation group BirdLife International. And a far greater number, perhaps approaching 6,000 species, have gone into general decline. In Great Britain, for example, 139 of 247 breeding bird species are in moderate to rapid decline, according to annual surveys. Some Australian ornithologists estimate that one in five of their native birds are threatened with extinction in the not-too-distant future.

Many biologists argue that extinction is just the last stage of decline, occurring long after a species ceases to function as a natural part of its ecosystem. As local populations die out, remaining populations become isolated, their genetic diversity impoverished. "Avian diversity is in major decline," says Nigel Collar, an ornithologist who monitors world bird diversity at BirdLife International. "Not only are more and more species edging closer to extinction, but an unknown number of subspecies and populations are disappearing, and species with continuous ranges are breaking up into isolated pockets of organisms, allowing less and less genetic interchange. Sometimes when we lose what we think is a mere population, we may be losing a virtual species, in terms of its genetic variation. And what is true for birds is of course true for all of the Earth's life-forms."

The Greatest Threat

Habitat loss and degradation endangers more birds than any other factor. Habitat is routinely destroyed by commercial logging, slash-and-burn clearing, industrial or urban development, intensive farming, and over-grazing, among other land uses. According to the U.N. Food and Agriculture Organization's State of the World's Forests report, the planet is losing 9.4 million hectares (over 23 million acres) of forest cover per year, even though that calculation counts all the natural forest that's converted into plantations as still forested, which from a bird's standpoint is a further loss. Of all the species identified by BirdLife International as threatened, 85 percent are affected by habitat loss. Of these, more than 900 live in forests, almost 400 in grasslands, and 150 in wetlands.

The diversity of birds, like that of insects, mammals, or trees, is highest in the tropics. Predictably, the...