Page 82 - The Miracle of Migration in Animals

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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