To help them soar, eagles use thermals which are rising currents of warm air and up-drafts generated by terrain such as valley edges or mountain slopes. Soaring is accomplished with very little wing-flapping, enabling them to conserve energy. Long-distance migration flights are accomplished by climbing high in a thermal, then gliding downward to catch the next thermal where the process is repeated. Several eagles soaring in a thermal together is described as a "kettle of eagles." (Courtesy of Marybeth Garrigan)
Bald eagles can fly to an altitude of 10,000 feet. During level flight, a bald eagle can achieve speeds of about 30 to 35 mph.
The tail - is very important for flight and maneuvering. While the bald eagle is soaring or gliding in flight, the tail feathers are spread in order to attain the largest surface area and increase the effect of thermals and up-drafts. The tail also helps to brake the eagle when landing and assists in stabilization during a controlled dive or swoop toward prey. The strength of the feathers and the follicles holding the feathers is quite impressive while watching the tail move back and forth and up and down during maneuvers.
Bald eagles have 7,000 feathers. Eagle feathers are lightweight yet extremely strong, hollow yet highly flexible. They protect the bird from the cold as well as the heat of the sun, by trapping layers of air. To maintain its body temperature an eagle simply changes the position of its feathers. While an eagle suns itself on a cold morning, it ruffles and rotates its feathers so that the air pockets are either opened to the air or drawn together to reduce the insulating effect. Feathers also provide waterproofing and protection, and are crucial for flight.
Immature golden eagle preening its feathers.
Feather structure makes pliability possible. Overlapping feathers can form a dense covering, which the birds can open or close at will. The bald eagle has several layers of feathers, each serving a different function. Under the outer layer of feathers is an inner layer of down or smaller feathers. The interlocking of feathers is an astonishing design of nature.
Birds puff up their feathers for various reasons. They puff them up while preening; to insulate themselves to changing temperatures; when they're relaxed; to make themselves appear larger when threatened; and when they're ill.
The feathers enable eagles to live in extremely cold environments. Eagles do not have to migrate to warmer areas each year to fulfill temperature requirements; they migrate to acquire available food supplies.
Eagles molt in patches, taking almost half a year to replace feathers, starting with the head and working downward. Not all feathers are replaced in a given molt.
A lone eagle feather is believed to convey great power. North American Indians incorporated the eagle's primaries and tail feathers into their ceremonies and legends.