Flying into trouble.

• Author: Youth, Howard
• Position: Birds - Cover Story

ALL OVER THE WORLD, BIRDS ARE IN DECLINE. SOME WILL NEVER BE SEEN AGAIN. BUT LONG AFTER THEIR PASSING, THE CAUSES OF THEIR DEMISE WILL CONTINUE TO HAUNT US -- UNLESS WE CAN MAKE PROFOUND CHANGES IN THE WAY WE VIEW OUR ENVIRONMENT

Visit some of the world's most environmentally compromised areas, and you will find plenty of birds. House sparrows hop between pedestrians' legs on New York City's crowded streets, common mynas nest in crumbling walls in downtown Delhi, flocks of hooded crows swirl over Moscow's polluted industrial districts. Thanks to such hardy survivors, there may never be a completely silent spring. As long as marginal water and air remain and a little vegetation pokes through the soil, at least a few types of birds will flourish. But most will not. As the planet's human population swells and spreads over once-wild areas, some 70 percent of the world's 9,600 bird species are responding with declines, and 1,000 species are threatened with extinction in the near future, according to a recent report by BirdLife International, a Cambridge, England-based conservation group that charts habitat and species loss.

The phenomenon of disappearing birds has not only alarmed ornithologists, but has caused apprehension among botanists, foresters, farmers, agronomists, and ecologists. What is alarming, beyond the direct losses taking place, is that birds, unlike many other life forms, are particularly good indicators of the health of other species--and of whole ecosystems. Just as coal miners once carried canaries into the mines with them to test for dangerous air, we can monitor birds at large to spot incipient dangers in the world at large. Birds are ideal environmental indicators: they live in every climate, respond quickly to changes within their habitats, and are easily tracked (even many of the more elusive species have loud calls). A diverse, healthy bird population is a good index for the overall well-being of an ecosystem. In the U.S. Pacific Northwest, for example, the continued wrangling over timber jobs and the remaining virgin habitat of the spotted owl affects the survival not only of the owl, but of the Pacific yew tree, the red-backed vole, and a spectrum of other species. When birds die off in unnatural numbers, however, what we are seeing is not just a warning of impending degradation, but a part of the degradation itself--a tearing of the ecological web that keeps the planer's health in balance. Birds are main players, as well as messengers. Large birds, such as owls, hawks, and crows, are essential to suppressing population explosions of rodents. Smaller birds, searching almost constantly for food to fuel their high metabolisms, prevent potentially devastating plagues of insects. The stomach of a single flicker (a North American woodpecker), for example, was found to contain five thousand ants.

While keeping animal pests in check, birds are essential to the vitality of plants. Hummingbirds and other nectar-feeding species pollinate a wide variety of flowers, including those too deep for insects to reach. Fruit-eating species act as winged protectors of forests, scattering tree seeds throughout their habitats via their droppings.

THE DYING OF THE WHITE STORK

Most bird species are declining because natural balances are being knocked askew by the global expansion of humanity: their habitat is being destroyed, or they are overhunted or poisoned or outcompeted by human-introduced species. But usually, the decline is caused by a combination of these factors. "Multiple causes are more often the rule than the exception," writes John Terborgh, director of Duke University's Center for Tropical Conservation, in his book on neotropical migrants, Where Have All the Birds Gone? A look into the life of the white stork, a species that has shared settlements with Europeans for centuries, illustrates the gauntlet many species must run just to survive in a human-dominated world. "White storks used to be common throughout Europe.... In some villages their nests adorned nearly every house," write Rudolf Schreiber and Antony Diamond in their report Save the Birds. But since the 1960s, according to censuses conducted throughout the birds' European range, breeding stork populations have fallen by two-thirds, and in many areas, they have disappeared entirely.

Though the white storks can nest in villages, they require nearby wetlands to supply them with frogs and other aquatic foods. Unfortunately, most European wetlands have been drained to make way for farms and development. And in the fall, when storks flee the northern cold to winter in sub-Saharan Africa, thousands of hunters, from Italy to Egypt, take aim at them as they soar southward along their ancestral flyway. Those that reach their African wintering grounds often land in agricultural fields laced with toxic pesticides and are stalked by subsistence hunters, who shoot them or catch the travel-weary birds with their bare hands. Those that survive the southward ordeal must repeat it northbound in the spring.

THEIR LAND IS OUR LAND

Even the freedom of flight cannot save many birds from the destruction of their feeding, breeding, and resting areas. To a wood thrush, bulldozers transforming a close-canopy forest into a suburban development are the equivalent of a hurricane raging through a human settlement. Over the millennia, most birds have developed a fixed menu of feeding and breeding needs linked to their particular habitats. A few have benefited from human alterations: birds like the rock dove (or common pigeon), the cattle egret, and many common backyard birds have undergone population explosions as wild habitats have yielded to buildings and farm fields, which simulate their traditional haunts (cliff ledges for the pigeon, open savannahs for the egret). But the majority of species have different needs, and where their habitat disappears, they vanish too. A quick tour of the world's habitats produces a grim...