When an eagle finds a thermal, it spreads its wings as wide as possible to increase its surface area and catch the maximum amount of air. As it dives downward through the thermal, the airflow over its wings causes them to generate lift, pushing the eagle upward.
Once the eagle reaches the top of the thermal, it uses its tail feathers to steer and maneuver itself to find another thermal. This way, eagles can stay in the air for hours without flapping their wings and travel long distances with little effort.