Page 158 - The Origin of Birds and Flight

g he way birds acquire propulsive force in flight is one of their

most impressive aspects. A great many features of bird
flight cannot be replicated technologically. A plane must
maintain a rather high speed in order to remain in the air, but birds also
make use of the air currents from their wing beats to fly more slowly. The
bird wing acts like a propeller. Another function of the wing
is to serve as a supporting surface. The high efficiency
of this function still cannot be achieved by technologi-
cal means.
One of the many problems that birds overcome
during flight is energy consumption: According to the
laws of physics, a specific level of energy is required