Page 51 - Design in Nature

Flawless Flying Machines: Birds 49

fused together. This design improves the strength of the bird's structure.
Another feature of the skeleton of birds, as mentioned previously, is that it is
lighter than in all other land-dwelling animals. For instance, the skeleton of
the dove weighs only about 4.4% of its total body weight. The bones of the
frigate bird weigh 118 gr, which is less than the total weight of its feathers.

2- Respiratory System
The respiratory system of land animals and birds operate on completely
different principles, primarily because birds need oxygen in much greater
quantities than do land animals. For example, a certain bird could require up
to twenty times the amount of oxygen
necessary for humans. Therefore, the lungs of
land animals cannot provide oxygen in the
quantities required by birds. This is why the
lungs of birds are created upon a much
different design.
In land animals, air flow is bidirectional:
air travels through a network of channels,
and stops at the small air sacs. Oxygen-
carbon dioxide exchange takes place here.
Used air follows a reverse course in leaving
the lung and is discharged through the
windpipe.
On contrary, in birds, air flow is
unidirectional. New air comes in one end,
THE SPECIAL LUNGS OF BIRDS
and the used air goes out the other end. This Birds have a very different anatomy from
their alleged ancestors, the reptiles. Bird
provides an uninterrupted supply of oxygen
lungs operate in a completely different
for birds, which satisfies their need for high fashion from those of land animals. Land
animals inhale and exhale air through the
levels of energy. Michael Denton, an same windpipe. In birds, however, the air
Australian biochemist and a well-known enters and exits through opposite ends.
A special "design" such as this has been
critic of Darwinism, explains the avian lung created to provide for the high volumes
in this way: of air needed during flight. Evolution of
such a structure from that of reptiles is
In the case of birds, the major bronchi not possible.
break down into tiny tubes which