Page 47 - Design in Nature

Feathers spring from a hollow cylindrical A chick that is 2-3 hours old primarily has
structure of the skin. feathers for warmth.
another like a zip with the help of these hooklets. For example, just one
crane feather has about 650 barbs on each side of the shaft. About 600
barbules branch off each of the barbs. Each one of these barbules are locked
together with 390 hooklets. The hooks latch together as do the teeth on both
sides of a zip. These barbules interlock so tightly that even smoke blown at
the feather cannot penetrate through it. If the hooklets come apart for any
reason, the bird can easily restore the feathers to their original form by either
shaking itself or by straightening its feathers out with its beak.
In order to survive, birds have to keep their feathers clean, well-
groomed and always ready for flight. They use an oil-gland located at the
base of their tails for the maintenance of their feathers. They clean and polish
their feathers by means of this oil, which also provides water proofing when
they are swimming, diving or walking and flying in rain.
In addition, in cold weather the feathers prevent the body temperature
of birds from falling. The feathers are pressed closer to the body in hot
weather in order to keep it cool. 17

Types of Feather
Feathers take on different functions depending on where on the body
they are located. The feathers on a bird's body have different properties from
those on the wings or tail. The full-feathered tail functions to steer and
brake. On the other hand, wing feathers have a distinct structure that
enables the surface area to expand during beating in order to increase forces
of up-lift. When the wing is flapped downward, the feathers come closer
together, preventing the through passage of air. When the wing is in an
upward movement the feathers open up, to give way to the passage of air. 18
Birds shed their feathers during certain periods in order to maintain their
abilities to fly. Worn or damaged large feathers are renewed immediately.