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Even before canaries were brought into coal mines to alert miners to the presence of poisonous gas, birds were giving us early warning calls signaling the earth’s deteriorating environmental health. Worldwide, some 1,212 of 9,775 bird species—one out of every eight—are threatened with extinction. Destruction and degradation of habitat is the number one danger, threatening 87 percent of these vulnerable birds.
As an ever-expanding human population has altered natural places around the globe—wetlands, grasslands, and forests—bird numbers have fallen. Global bird populations have shrunk by up to 25 percent since pre-agricultural times, largely because of conversion of habitat to farms. Over the past 300 years, farmland has expanded from 6 percent of the earth’s surface to nearly a third.
Today three quarters of threatened bird species depend on forests as their principal habitat; each year, however, some 13 million hectares of forests are destroyed, an area the size of Greece. Nearly half the forests lost are relatively undisturbed primary forests that are home to a number of sensitive birds and other creatures.
The sharpest declines in avian populations in recent years have come in Asia, particularly in Borneo and Sumatra, where lowland moist tropical forests are disappearing at an astonishing rate. By 2000, some 40 percent of Indonesia’s forests had been cleared. Now three out of every four bird species that depend on Sumatra’s lowland forest are on the verge of extinction. In addition to the loss of forests due to logging for lumber, the increasing demand for palm oil—recently prized as a biofuel—has raised pressure to convert natural forests to palm plantations. Without a rapid reversal of deforestation trends, all the lowland forest could be lost within a decade. Overall, some 118 of Indonesia’s bird species, including several endemic parrots and cockatoos, are threatened with extinction—the highest number of any country.
Close behind in numbers is Brazil, where 115 bird species are threatened. Both the Amazonian rainforest and the savannah-like cerrado are being cleared for ranches and farms, most recently for large-scale soybean production for feed, food, and fuel. In addition, Brazil’s Atlantic rainforest has shrunk by 90 percent, squeezed by growing cities and farms. This fragmented forest is home to some 950 kinds of birds, 55 of which are endemic and threatened.
Since 1500, 150 species of birds are believed to have disappeared entirely. Some 50 of these extinctions were the result of overhunting. Hunting brought the demise of North America’s passenger pigeon, once the most numerous bird on earth, within a human lifetime. Direct exploitation, including hunting for food and capture for the pet trade, is the second greatest danger after habitat loss, affecting nearly a third of threatened bird species today. (See data.) Fifty-two of the world’s 388 parrot species are at risk from overexploitation.
The intentional or accidental introduction of non-native species is the next greatest danger, affecting 28 percent of the world’s threatened birds. As people travel to all parts of the globe, so too do the pests and pets that prey on, out-compete, or alter the habitat of native wildlife. Introduced rats and cats alone have led to the extinction of 50 bird species. In the Hawaiian Islands, introduced predators and diseases have compounded problems of habitat loss and knocked out more than half of the 100-plus endemic bird groups. Possums, rats, and other mammals brought into New Zealand in the past 200 years have ravaged the once-abundant diversity of large birds that had evolved over 80 million years with no natural predators.
Pollution poses an additional risk, affecting 12 percent of the threatened bird species. In India, Gyps vulture populations have plummeted by 95 percent in less than a decade, many poisoned by medicine used to treat the livestock they feed on. Populations of common Western European farmland birds dropped by 57 percent between 1980 and 2003, with much of the decline attributed to the intensification of agriculture. In addition to direct poisoning from fertilizer and pesticide applications, runoff of chemicals contaminates the wetlands that migrating waterfowl rely on. Persistent organic pollutants, such as DDT residues, dioxins, and polychlorinated biphenyls, accumulate in the food chain and can lead to deformities, reproductive failure, and disease in birds.
Climate change is a relatively new threat to birds and other wildlife. Worldwide, a third of plant and animal species could become extinct by 2050 as a result of climate change. Over the last three decades, global temperatures have risen by 0.6 degrees Celsius (1 degree Fahrenheit), bringing changes to the migration, breeding, and habitat ranges of some birds. For example, as spring has come earlier in the Netherlands, so too has the emergence of the caterpillars that great tit birds need to feed to their nestlings. Unfortunately, the birds’ egg-laying date has not shifted, putting the hatching of the chicks out of sync with their food supply.
Birds that spend all or part of their lives at the earth’s poles are particularly vulnerable to rising temperatures. The migratory waterbirds in the Arctic will lose out as warming alters this vulnerable ecosystem. In the Southern Hemisphere, where 10 of the world’s 17 penguin species already are threatened, conditions will not improve as global temperatures increase by a projected 1.4–5.8 degrees Celsius ( 2.5–10.4 degrees Fahrenheit) during this century.
In addition to these looming threats, 7 percent of threatened bird species are at risk from incidental mortality. A rapid decline in seabird populations over the last 15 years corresponds with the growth in commercial longline fisheries. Each year these operations kill some 300,000 seabirds that are tempted by bait and then ensnared. All 21 species of albatross are now threatened or near-threatened because of run-ins with the fishing industry. Birds also fall prey to industrial development, which endangers more than half of the threatened birds in eight Latin American and Caribbean countries. In Europe, Central Asia, and Africa, electrocution on power lines has caused the mass mortality of raptors. And hundreds of millions of birds in the United States die each year from collision with windows, the number one cause of U.S. avian mortality.
If birds disappear, so do the economically valuable services they provide. Birds pollinate flowers, disperse seeds, and help to eliminate rodents, insects, weed seeds, and other pests. Scavenger species recycle nutrients and clean up dead and decaying animals that might otherwise be sources of disease.
Preventing the decline and extinction of additional bird populations depends largely on protecting the world’s remaining wild spaces and preserving the health of our natural and altered ecosystems. For species that are critically endangered, more-intensive management may be needed if population numbers are to return to a viable level. This may include captive breeding and re-introduction, and the active removal of invasive predators to the extent possible. To prevent the spread of avian disease, more stringent biosecurity is needed to limit contact between infected domestic flocks and wild birds. Diverting birds away from artificial structures—buildings, towers, and turbines—and siting new construction outside of migratory paths also could prevent avian fatalities.
Reports this past spring that the ivory-billed woodpecker, long thought to be extinct, is still with us thrilled birdwatchers and others, but this sort of second chance seldom occurs in nature. Even with continued habitat protection, once wildlife populations drop dramatically, a rebound is far from guaranteed. And without stabilizing climate and human numbers, putting fences around all the parks in the world will not be enough to protect threatened species.
Copyright © 2005 Earth Policy Institute