Page 82 - The Miracle of Migration in Animals
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THE MIRACLE OF MIGRATION IN ANIMALS


                     Why Migrating Birds Have Long Wings


                     Species of birds that migrate have longer wings than non-migra-
                 tory ones. This reduces wing-tip drag and creates a more effective lift
                 as well as a more efficient wing area to body weight ratio. In addition,
                 the outer primary feathers (that, together with the inner feathers, ef-
                 fectively thrust the bird forward in flapping flight) tend to be longer
                 in migrating birds, lending the wings a pointed rather than a rounded
                 shape.
                     This shape can be observed in a number of migrating birds. For
                 example, the black-naped oriole, which travels between Siberia and
                 India, has pointed wings in common with the albatross, the falcon,
                 the swift, various species of shorebird and tern, and other long-dis-
                 tance travelers. 24


                     Aerodynamic Advantages of Curved
                     Wings


                     There is an important reason for curvature in birds’ wings. Close
                 observation reveals that the wings of aircraft have this same curva-
                 ture. An aircraft’s wing is designed for flight and has a special shape
                 known as an airfoil, also found in fans and propellers.  Airfoils create
                 a lifting force when subject to airflow. An airfoil has a thicker,
                 rounded leading edge and a very fine trailing edge. Between the lead-
                 ing edge and the trailing edge, both the upper and lower surfaces of
                 the wing are curved. The upper surface usually has a greater curve
                 than the lower and, in aviation terminology, this humped sur-
                 face is known as “camber.”
                     Airfoils make use of the Bernoulli’s principle, according
                 to which an increase in the velocity of a stream of fluid results in a de-







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