Flying into trouble.

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 picture for the future of birds and the other life forms to which they are linked. As the last large pockets of tropical forest--home to at least 3,500 bird species--fall to satisfy human needs for food, lumber, and minerals, the birds' wings fail them; there is no refuge to which they can escape. Even Amazonia and the expansive forests of New Guinea, not long ago considered impenetrable wilderness, will most likely not last another century of abuse.

Temperate and boreal forests, too, are under attack. From Siberia to southern Australia, once-vast tracts have been hacked into patchworks of woods and openings that give greater advantage to bird predators by depriving the forest birds of protective cover. At the same time, the clearings reduce the birds' forest-dependent food base. As a result, even once-abundant species are disappearing: populations are declining for the hooded robin in southeast Australia, the wood thrush in eastern North America, and a vulture-sized partridge called the capercaillie in the Eurasian taiga.

Less publicized than the savaging of forests, but with similar consequences for birds, has been the demise of the world's natural open spaces--which are ecologically quite different from the clearings chopped out of woodlands. As grazing and plowing chew away at the remaining native grasslands of Pakistan, India, or Spain, once-plentiful bustards and other birds of the open plains disappear along with the grasses. The same pattern can be seen in the collapse of prairie chicken populations on the great plains of North America, and of the ostrich-like rheas of the South American Pampas.

But it is not only on dry land that birds are threatened. Wetlands, which are breeding, resting, and feeding grounds for waterbirds ranging from pelicans to sandpipers, are being drained all over the world (see the review of Wetlands in Danger in this issue). The United States Fish and Wildlife Service (USFWS), for example, estimates that 53 percent of the country's wetlands remain--a statistic that is grimly reflected in the steady decline of waterfowl dependent on these areas. USFWS surveys show a 30 percent drop in the populations of North America's 10 most common duck species, from 37 million in 1955 to 26 million in 1992.

Meanwhile, throughout the coastal tropics, mangrove forests that provide nesting and feeding grounds for aquatic life and waterbirds continue to be cut for timber, beach resorts, and conversion to shrimp farming for upscale consumers, leaving coastlines more vulnerable to erosion and pollution.

In many places, too, entire mosaics of ecosystems--woodland, wetland, grassland--face obliteration by massive dam projects. The Sardar Sarovar project now underway in northwest India, for example, and the gargantuan James Bay system in Quebec, have drowned the homes of uncountable numbers of birds. The James Bay project alone is expected to immerse an area the size of California. INGESTING PESTICIDES

A more insidious threat to birds comes from the pervasive spread of chemicals. DDT, considered a miracle pesticide during World War II, was found to be an environmental menace after populations of pelicans, falcons, and eagles collapsed in Europe and the United States in the 1950s and 1960s. As these hunting and fishing birds gathered DDT-tainted prey, the chemical accumulated in their tissues, causing them to lay eggs with flimsy shells that cracked under the incubating parents' weight.

In the early 1970s, after environmentalists had traced DDT as the cause of the population declines, the chemical was banned in most western countries--and many of the birds have since rebounded. But DDT remains one of the cheapest and most widely used insecticides in many developing nations. Twenty studies of the effects of DDT and its derivatives on six species of African birds-of-prey have shown that DDT-caused thinning of eggshells is "high enough to cause a decline in local populations," writes Humphrey Crick of the British Trust for Ornithology in the New Scientist. Some countries, including India, have banned DDT as an agricultural pesticide but still use it widely to battle malaria-carrying mosquitoes. Spraying for tsetse flies in western Zimbabwe, according to a British Overseas Development Administration study, has been the main cause of DDT contamination in birds, freshwater fish and mussels, and bats in that area.

DDT is only the most highly publicized of the chemical threats to birds. The dangers of human-made chemicals--which are quickly developed, but usually poorly tested--typically come to light only after many birds have been poisoned. Reporting on a pesticide called fenitrothion, Crick wrote: "The dosage rates used against locusts during the campaigns in Africa in 1986 and 1987 would kill most birds caught in the spray." Carbofuran, a pesticide that was spread on fields in granulated form, was banned in 1991 by the United States Environmental Protection Agency (which will phase out its use over a period of years), after it killed tens of thousands of birds in Virginia, according to the National Audubon Society.

BATHING IN CHEMICALS

The toxic residues of agriculture and industry often wash into the waters birds drink and feed in. One common effluent is mercury, a by-product of coal-burning power plants, and a common fungicide in papermaking. Much of the mercury ends up in lakes, rivers, and estuaries. Where fish ingest mercury, so do birds--and, often, humans. Defenders of Wildfire, a Washington-based conservation organization, reports that high levels of mercury were found in the tissues of cared grebes, waterbirds that mysteriously died at southern California's Salton Sea in the spring of 1992. The dead birds also contained high levels of selenium, an element that builds up to toxic levels in agricultural runoff. Altogether, 150,000 cared grebes washed up on the shores of the "sea," which serves as a drainage area for three polluted rivers. Though the chemicals may not have been the only cause of the birds' death, they seem certain to have played a role. Selenium poisoning has also been blamed for hundreds of birth defects and high embryo mortality in waterbirds nesting at a number of other western U.S. wildlife refuges.

Rod and gun enthusiasts have been creating another toxic nightmare for birds: lead poisoning. Loons, swans, ducks, and other waterfowl are as likely to die from eating shotgun pellets as from getting hit by them, in places where hunters prowl. Lead-shot bans have recently gone into effect in the United States, Canada, and Denmark, where hunters will now use non-toxic steel shot. In Britain, fishers can no longer use lead sinkers. But outside the ban areas, lead contamination continues as waterfowl swallow the spent buckshot or discarded sinkers while foraging for food, then succumb to poisoning within a few weeks. The opalescent sheen of oil, so commonly seen on wet roads, also marks the spots where thousands of birds have met grisly deaths each year. When seabirds come into contact with spilled oil, those that aren't poisoned often die from hypothermia, since they lose their insulation and waterproofing once their feathers are mired. The Exxon Valdez oil spill in March 1989 killed 300,000 birds, and was the largest chemical-caused bird die-off in North American history. Tallies for most other spills are less precise, but the avian casualties of the Persian Gulf War must have been just as catastrophic. That war not only destroyed wetlands and nesting grounds but gave a new meaning to the concept of a desert "mirage" by leaving behind shimmering inland lakes of oil--which to birds in the air looked like water. Thousands of waterbirds landed in these "lakes" and became fatally mired. Each year, of course, hundreds of smaller, but still damaging, oil spills (some accidental, some not) occur worldwide.

Acid rain makes once-prime habitat uninhabitable to fowl, fish and other lifeforms. Acidification caused primarily by sulphur dioxides and nitrogen oxides from industrial plants and motor vehicles gathers in clouds and rains down an acidic brew that sterilizes remote lakes and defoliates forests.

The planting of non-indigenous species of plants can have a similar effect. In Wales, for example, populations of a semi-aquatic bird called the dipper have disappeared in places where fast-growing conifer plantations have been planted to replace native oak woods--a transformation that has occurred over some 10 percent of the Welsh countryside. In these areas, acids washing off the conifers' needles have contaminated nearby streams, killing off aquatic insects and small fish--thereby depriving the dippers of their main sources of food. RAINFOREST CRUNCH

"Birds are the earth's global ambassadors. They recognize no human-made boundaries, only those of the natural world," write Schreiber and Diamond. This is especially true for long-distance migratory birds. The mysterious 75-percent drop in whitethroat warbler populations breeding in Britain over the past 27 years turned out to be caused by expanding drought and desertification in this bird's distant wintering grounds in the African Sahel. Those concerned about the health of migrating British birds, therefore, must also care about the environmental state of affairs in Africa.

On the other side of the Atlantic, American and Canadian scientists are scouring habitats as far south as Argentina for clues to the decline of many familiar North American birds. At least half of the neotropical migrants, the 250 species breeding in North America but wintering in points south, have declined significantly in recent years. According to USFWS records from 1978 through 1987, 44 of the 62 surveyed neotropical forest species declined, including some of the more common species: the yellow-billed cuckoo (down 5 percent per year), wood thrush (4 percent), black-throated green warbler (3 percent), and northern oriole (2.9 percent).

Over the past 10 years, as research in the neotropical migrants' wintering areas has intensified, researchers have discovered many species to be particularly vulnerable because of their limited winter ranges. Duke University's Terborgh estimates that more than 50 percent of neotropical migrants winter in Mexico, the Bahamas, and Greater Antilles islands, a much smaller area than their summer haunts. Deforestation in these tropical areas has been acute: most of the evergreen, deciduous, and mangrove forests the birds concentrate in have been cut and planted over with crops or exotic vegetation. Those few migrants that can tolerate such transformed habitats risk increased exposure to pesticides once they venture out of the natural forest. The condition of the birds' breeding grounds is not healthy either. "Taking into account a 40 percent reduction in the total area of eastern (North American) forests, the fragmented . . . state of most of today's forest, and the prevalence in the South (U.S.) of biologically sterile pine plantations . . . the current populations of forest-living tropical migrants are probably no more than a quarter of their presettlement levels," writes Terborgh. The increasing number of cleared areas (for roads, developments, powerlines, and the like) in these woodlands has increased the pressure on the birds, as populations of egg- and nestling-eating predators like opossums and blue jays have exploded, and the brown-headed cowbird, an open-area blackbird that lays its eggs in other species' nests, has become much more abundant. In many areas, cowbird eggs can now be found in more than half the songbird nests. Young cowbirds, stronger and more aggressive than their hosts' young, usually kill or starve their nestmates. Neotropical forest birds are primarily insectivores, devouring large numbers and varieties of insects, including harmful forest pests like the spruce budworm, gypsy moth, and tent caterpillar. Although no definitive studies have yet been done, it seems likely that a decline in the numbers of these birds could result in more frequent pest epidemics. The birds that have remained stable, or increased in numbers, are mostly the year-round residents, which have more varied diets and may not eat as many pests.

In southeastern Australia, woodland fragmentation has raised troubling ecological questions. "The loss of . . . birds from isolated woodland patches may eventually lead to a decline in the seed set of bird-pollinated plants," writes Doug Robinson, who researches bird declines for the Royal Australasian Ornithologists Union. "The loss of white-winged choughs, painted buttonquail, and babblers (in southeast Australia) . . . means that no bird species remain to turn over the (leaf) litter and weed out annuals." The disappearance of these underbrush-tending species could bring about drastic changes in the botanical composition of the forest.

Though effective hunting regulations prevail in North America and Britain, unregulated hunting and trapping in most other parts of the world claim tens of millions of birds each year. In Cyprus, a small island nation set along a major Mediterranean migration path, about 3 million transiting birds are shot each year for fun or food, reports the U.S.-based National Audubon Society. In Greece, at least 700,000 "protected" birds are gunned down annually, according to the Hellenic Society for the Protection of Nature. Hundreds of thousands more are shot as they pass over Egypt.

On the European mainland, culinary tastes have turned orioles, finches, and other songbirds into tempting targets. Italians snare them, the French catch them in nets, and the Spanish trap them by daubing glue on tree branches--all to garnish dinner plates. In Italy alone, despite "legal protection," 50 million songbirds are killed for diners seeking bite-sized delicacies each year. SNAKES AND CATS

Bird species also succumb to the predations of animals that are not a part of their evolutionary ecosystem, but are disruptively introduced--whether or not wittingly--by migrating humans. In the 16th and 17th centuries, an exotic menagerie normally followed European explorers to new islands and continents: most ships unintentionally deposited rats at their ports of call, while intentionally introducing goats, cats, mongooses, and dogs--which feasted on the local foliage or fauna. In most places, these introductions shattered fragile natural balances and caused rapid extinctions.

Today, introduced species continue to devastate bird populations. A study in Britain, for example, found that the country's domestic cats had killed 20 million birds. A survey conducted in the Australian state of Victoria, similarly, estimated that the 500,000 cats in Victoria kill 13 million small animals a year, including members of 67 native bird species.

Accidentally introduced animals can be just as devastating. The brown tree snake, for example, arrived on the Pacific island of Guam around the early 1950s in cargo shipments from Australia, New Guinea or the Solomon Islands. By 1986, the snake had eaten four of the island's five endemic bird species into extinction (one, the Guam rail, was extinct in the wild but has been bred in captivity and rereleased on a nearby--snake-free--island; the other three are extinct). The island's small mammals and reptiles have also suffered; Guam had never had a predator that ate serpents, so the snakes have proliferated. In the United States, the eastern bluebird and red-headed woodpecker, two of the most common backyard birds last century, have been diminished throughout their ranges by the more aggressive, introduced house sparrows and starlings, which oust these birds from their nests in tree cavities.

THE PACE OF EXTINCTION

Many species of birds have benefitted from nature reserves set aside to protect their wintering, migrating, and breeding grounds. But existing sanctuaries constitute less than 5 percent of the world's land area--a good part of which is barren tundra or desert. And even in these areas, wildlife often cannot be adequately protected. The civil war in Rwanda, for example, has left that country's few remaining gorillas and threatened forest birds in an extremely vulnerable situation as game wardens and tourists have fled the Parc des Volcans National Park--which until last year was the country's second largest source of foreign exchange.

Even without war, many of the world's parks are safe havens only on paper. Poaching and encroachment into protected habitats occur on every continent. In Mexico's Ixta-Popo National Park, free-ranging cattle strip vegetation from the grassy woodlands; in India's Guindy National Park, the park's only dry-season watering hole is drained to supply nearby housing developments with water; and in Taiwan's Kenting National Park, hunters make an annual event of shooting gray-faced buzzard eagles.

Troubles abound also in U.S. parks, which have long provided a model for other countries aspiring to protect their wild heritage. All told, the USFWS administers more than 91 million acres of wildlife habitat, much of it in the country's 470-unit national wildfire refuge system. A 1991 USFWS study found that activities harmful to wildlife--from military bombing and mining to logging--were occurring on 60 percent of the country's refuges. The study did not account, however, for such harmful secondary threats as oil spills or industrial and agricultural runoff like that which flows into the Salton Sea National Wildlife Refuge.

Bird extinctions at the hands of humans are not new, but are increasing at an alarming rate. In the Polynesian Islands, about 35 of 50 now-extinct species were killed off by the islands' inhabitants well before Captain James Cook arrived there in 1778, according to a study by the Washington, D.C.-based Smithsonian Institution. Since the 1600s, some 150 bird species have been lost, including North America's passenger pigeon--one of the world's most abundant birds (more than 3 billion) until the second decade of this century, when deforestation and overhunting wiped it out. Some of the most recent losses include the Atitlan grebe in Guatemala in 1987, the imperial woodpecker of Mexico (last seen in 1958), and possibly the Bachman's warbler (last seen in 1981), a small yellow and black bird that bred in southeastern U.S. swamp forest and wintered in Cuba's evergreen forest before it was converted to sugarcane fields.

The pace of bird extinctions--along with those of other animals and plants--appears likely to accelerate rapidly. Many scientists predict that humanity is about to cause the greatest wave of plant and animal extinctions since the die-off of the dinosaurs 65 million years ago, and many of the first victims will be birds.

HUMAN ALLIES

Not all of humankind is resigned to participating in this ornithicide, however. Birds, with their inspiring powers of song and flight, have strong allies. In the past few decades, the ranks of amateur naturalists have swelled worldwide, aiding scientists in censuses and conservation efforts. The Britain-based IWRB, for instance, has been able to expand its operations because citizens in more than 70 countries in Europe, Africa, Asia, and Latin America have conducted many of the organization's bird surveys and conservation efforts. Meanwhile, countrywide winter and breeding bird surveys are drawing thousands of volunteers each year in the United States, Canada, Japan, Australia, and Britain. Unfortunately, developing nations still lag far behind in these activities, and many of their bird populations remain poorly studied. Nonetheless, international concern over wildfire conservation was given greater prominence by the signing of the biodiversity treaty at the Rio Summit in 1992. An increasingly global approach to conservation is emerging--one that emphasizes not just individual species, but entire ecosystems.

A BirdLife International study published in 1992 revealed that 20 percent of all bird species were confined to two percent of the earth's surface in pockets of endemism it called Endemic Bird Areas, or EBAs. But EBAs are not just special places for birds. "Wherever avian endemism is pronounced, usually there also appears to be a high degree of endemism in other life-forms," notes the report. A majority of these hotspots fall in tropical countries: of a total of 221 EBAs tallied, two-thirds occur in the tropics. Ultimately, only widespread concern within these high-diversity countries, and particularly within the endemic areas, can avert a devastating wave of extinctions. In the long run, therefore, global efforts to organize bird-saving projects will only succeed in raising consciousness and preserving essential habitat if there is a strong local interest, especially in the vulnerable tropics. Each nation can start by protecting key areas and engaging local people to zealously enforce its wildlife laws. That may be difficult, though, since the tropical countries where biodiversity is greatest--and bird habitats are most decimated--are likely to be the very ones where widespread poverty and government corruption tend to keep funds away from wildlife programs and education. FAREWELL

It is January, and Europe's white storks are now Africa's white storks. Though traditionally these birds have been considered good luck, their own luck may be running out. In a few decades they may be gone. People will sadly recall the white and black birds that once strutted across their fields or nested atop local church steeples. But will the stork's extinction bring more than a sentimental farewell?

Certainly, when there are no longer enough wetlands to sustain these leggy birds, scores of other species will also have vanished. If pesticides have contaminated storks, they will also have done damage to other creatures, including humans. And if the stork--a bird inhabiting our folklore and settlements for ages--cannot thrive under rapidly changing global conditions, how long can we?"

On Their Last Legs?

Green spots mark the habitats of threatened species generally found nowhere else. These "endemic" birds are classified according to how severely they are threatened:

* Critical need for protection. The threat of extinction is highest for these areas.

* Urgent need for protection.

Not shown is a third category of endemic areas for which the threat is slightly less severe but still "high--which if included would roughly double the number of spots on the map. Also not shown are any of the thousands of bird species that are more widespread and therefore in less danger of imminent extinction, but are nonetheless declining in numbers--such as the majority of North American neotropical songbirds.

TABULAR DATA OMITTED

Howard Youth, a former associate editor of World Watch, is now a freelance writer in Madras, India.