Large wingspan
Eagles have a very large wingspan, which gives them a lot of lift. This means that they can stay in the air with a minimum of effort.
Lightweight bodies
Eagles are also very lightweight birds. This is due to the fact that they have hollow bones and a high proportion of muscle to fat. This allows them to fly more easily than heavier birds.
Updrafts
Eagles seek out updrafts, which are currents of rising air. These updrafts can be created by a variety of things, such as the heating of the ground by the sun, the collision of two air masses, or the movement of air over mountains. When eagles find an updraft, they can use it to gain altitude without having to flap their wings.
Soaring is a very efficient way for eagles to travel. They can cover long distances without expending a lot of energy. This is important for eagles, who often need to travel long distances in order to find food and nesting sites.