The avian skeleton combines lightness with strength. The bones are thin and hollow. Many bones are fused, so the skeleton is more rigid than the skeleton of a reptile or mammal. The rigid skeleton provides stability during flight. Note in Figure 42-4 that the bones of the trunk and hip vertebrae and the pectoral and pelvic girdles are highly fused. Along with the furcula, the large, keel-shaped sternum, or breastbone, is an attachment point for flight muscles. The humerus, ulna, and radius, along with the pectoral girdle and the sternum, support the wing. The pygostyle (PIEG-uh-stiel), the fused terminal vertebrae of the spine, supports the tail feathers. The tail provides additional lift and aids in steering and braking.
Flight involves a series of complex wing movements, each one using a different set of muscles. On the downstroke, the wings cut forward and downward through the air. During upstroke, they move upward and backward. These movements are made possible by large, powerful flight muscles in the breast and wings. In some birds, flight muscles account for up to 50 percent of the body weight.
Materials pictures of different kinds of birds, ruler Procedure Examine each sheet of birds and their wings. Compare the structure and shape of the wings. Measure the wingspan relative to the bird's body length. Record your observations.
Analysis Predict the type of habitat in which each bird lives. How does the shape of the wing relate to the bird's niche? Explain why the type of wings each bird has might make the bird unsuccessful if it were introduced into a much different environment.
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