Even before canaries (特高频噪声) 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. Global bird populations have shrunk by up to 25% since preagricultural (农业社会前的) 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.
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 pa
A. Loss of forests that are home of birds.
B. Toxic chemicals that may cause diseases to birds.
C. Their habitat area in Greece that has been destroyed.
D. Animals from other continents by the process of globalization.
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