Empty skies.

• Author: Larsen, Janet
• Position: EYE ON ECOLOGY

EVEN BEFORE CANARIES were brought into coal mines to alert workers 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 are faced with extinction. Destraction and degradation of habitat is the number-one danger, threatening 87% 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% since preagricultural times. Over the past 300 years, farmland has expanded from six percent of the Earth's surface to nearly 33%.

Today, three quarters of threatened bird species depend on forests as their principal habitat; each year, however, some 13,000,000 hectares of forests are destroyed, an area the size of Greece. Nearly half the woodlands 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 tropical forests are disappearing at an astonishing rate. By 2000, some 40% 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 Jogging for lumber, the increasing demand for palm oil--recently prized as a biofuel--has raised pressure to convert natural forests to palm plantations.

Direct exploitation, including hunting for food and capture for the pet trade, is the second greatest danger after habitat loss, while next is the intentional or accidental introduction of non-native species. 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 80,000,000 years with no natural predators.

Pollution poses an additional risk, affecting 12% of the threatened bird species. In India...