Bald eagles can reach great heights when flying. Using thermal convection currents(对流)，they can climb up to 3，000 m in the air. They can soar for hours using these currents. When cruising，they can fly about 65 km/hr. In addition，if their water source freezes，bald eagles may use thermal convection currents to migrate in the winter.

　　Preferring to make their homes in large trees near bodies of water(both fresh and salt)，bald eagles build enormous nests out of sticks. Generally speaking，their nests are at least half a meter deep and 1.5 m across but can be bigger. These giant nests have been known to weigh up to 900 kg.

　　A mating pair produces up to three eggs a year，though it is not likely that all three will survive. Both parents take turns hatching the eggs. While one is hatching，the other searches for food or more nesting materials.

　　In 2007，the bald eagles was removed from endangered and threatened species list kept by the United States Fish and Wildlife Service. In addition， IUCN’s Red List currently considers the bald eagle as a species of least concern of extinction. Their successful recovery is due to years of conservation efforts along with the ban on the pesticide(农药)DDT in 1972. While bald eagles have few natural enemies and are no longer considered endangered，threats still exist to the bald eagle，including habitat loss. As people move to the shores，they are cutting down trees and forcing eagles to make their homes elsewhere. Illegal hunting is another threat.

    ……

    更多精彩请阅读《高中生》杂志！