Surviving these long distance migrations is not easy! Over time, birds have evolved some impressive adaptations that help aid in their journeys. Watch this TED-Ed video to learn more about how evolution works.
One of the most noticeable adaptations is the development of feathers in all bird species. While feathers serve many purposes other than flight, a specialized set of tail and wing feathers allow birds the additional ability to take to the skies. On each wing, flight feathers known as remiges are responsible for providing the propulsion and lift that birds need to get off the ground. The tail feathers, or retrices, help stabilize during flight and provide additional control during descent. Between the flight feathers and other specialized feathers, different bird species can have a few hundred to over 25,000 total feathers at any one time.
Another important evolutionary characteristic is the unique skeletal system of birds. Deceptively, a bird’s skeletal system is typically only about half the weight of its feathers. This is because most birds have hollow wing bones that retain their strength through internal struts (to see an image of a wing bone cross-section, click here). Besides hollow bones, the fusion of bones in the back and pelvis help provide additional stability during flight as well as absorb shock both during flight and landing. Overall, these adaptations allows for bones to remain relatively light yet strong, both important traits when trying to get off the ground.
During flight, bird’s highly efficient respiratory systems allow them the ability to extract more oxygen from every breath than any other vertebrate. This is because birds have lungs as well as a set of anterior (front) and posterior (rear) air sacs, which act as bellows to keep a continuous flow of air through lungs. How does this work? In order to understand bird respiration, we need to break air movement down into four steps. When birds first inhale, the posterior air sacs pull in fresh air from the outside world. Upon exhalation, this air is pushed into the lungs where oxygen is extracted through gas exchange. A second inhalation moves the now depleted air into the anterior air sacs, while simultaneously a new batch of fresh air is moving into the posterior air sacs. A second exhalation moves the depleted air back out of the bird, while the air that was in the posterior air sac moves into the lungs. Click here to learn more about this highly efficient system and to watch an animation how air moves through the lungs.

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