Flight Adaptations

Skeleton:

When reading this section, you can look at the picture of the skeleton of a modern bird. This will give you a visual understanding of the structure of the modern bird. Also, when reading this section and looking at the skeleton, and keep in mind the evolutionary process that brought on these structural adaptations for flight.

There are many modifications connected with flight:

The most obvious skeletal adaptations are the wings, from short, stubby, and weak arms. Along with the change in the wrist and fingers structure, function and actions. The wing evolved from the basic forelimb with five toes used for walking. The shoulder has moved up so that the bird's body, and its centre of gravity, hangs below the wings to provide stability. The humerus (upper arm bone) is usually short, particularly in birds with a rapid wing beat, such as hummingbirds, but is long and slender in gliding birds (if an albatross flapped its wings like a hummingbird they would snap). The shoulder is a 'universal' joint, which means that the humerus can rotate in the complex movements of flapping and folding the wing. In contrast to reptiles and mammals, however, its main movement is up and down for flapping, rather than to and fro for walking. The greatest anatomical change in the bird's wing has taken place in the wrist and hand. Most of the bones have fused together or have disappeared entirely. The wings functions are both as a lifting surface and a propeller, so it must be rigid enough to withstand considerable forces of lift and drag yet remain flexible enough for the complexities of flapping flight.

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