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Bone Structure
Carninates have specially developed bones for flying. They are hollow and almost spongey in apperance in order to keep the bird light, and Carinates have large "keeled" sternums that provide maximum surface area for flight muscles to attach to. Ratites have larger, heavier bone structure characterized by flat sternums.
 Metabolism
The majority of birds have extremely fast metabolisms. The average resting bird has a body temperature of 104 degrees Fahrenheit, which allows them to be activity in colder temperatures. However, maintaining this body heat as well as flying, a physical trying process, requires that birds eat a lot every day. Birds are diverse eaters; while some hunt for insects, small mammals, fish, and even other birds, others depend on seeds, fruits, or nectar as part of their diet.
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The bone featured above is from the wing of a bird, and the notches are used to firmly root flight feathers into place.
Respiratory System
The respiratory system of the bird is set up so that it has a constant supply of fresh air to the lungs at all times. When the bird inhales, 75% of the air from that breath is stored in the air sacs all over the bird's body, and the remaining 25% goes to the lungs. As the bird exhales, the air from the sacs rushes to the lungs, keeping a supply of fresh air available to the bird.
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