Gliding and Soaring

Golden Eagle (Aquila chrysaetos). Lopez Island, Washington. April. Photographer: Peter Cavanagh

Golden Eagle (Aquila chrysaetos). Lopez Island, Washington. April. Photographer: Peter Cavanagh

Migrating birds, like the Golden Eagle (above) often soar using currents of rising air to lower the energy cost of their long flights. Uneven heating of the surface of the Earth by the sun generates these currents, which are called thermals.

The long, broad wings of the Golden Eagle are well suited to soaring. The increased drag that results from this wing shape (see “Wing Size and Shape”) does not cause major increases in energy expenditure because the ride upwards is “free”.

Schematic illustration of soaring in a thermal to gain height then gliding to the next thermal.

Schematic illustration of soaring in a thermal to gain height then gliding to the next thermal.

A bird will ride a thermal to gain height (above), circling along with the rotating air. This requires only a small amount of energy to maintain wing position. As the speed of the updraft slows, the bird will flap briefly to leave the air current and glide downwards in the migratory direction in search of another thermal.

The presence of clouds, which appear above thermals, and dark ground which promotes thermal formation, are probably signs that birds use them to find rising air.

LEARN MORE ABOUT GOLDEN EAGLES

KIDS QUESTION: In the museum exhibit, we asked: What does the term “pecking order” mean?

The answer is: It means that some birds always get the first pick when food is available and those lower in the pecking order have to wait their turn.

In the US, the Golden Eagle is usually top of the pecking order and you can see Bald Eagles, Turkey Vultures, and Crows waiting their turn (in that order) when food is on the ground.