Page 59 - Design in Nature

Flawless Flying Machines: Birds 57

Soaring in the Wind
Birds further reduce the energy consumed by utilising winds. They
soar by increasing airflow on their wings and they can remain "suspended"
in sufficiently powerful air currents. Up-drafts are an added advantage to

them.
Making use of air currents in order to save energy in flight is called
"soaring". The kestrel is one of the birds with this capability. The ability to
soar is a sign of birds' superiority in the air.
Soaring has two major benefits. Firstly, it conserves energy needed to

stay in the air while searching for food or defending the feeding ground.
Secondly, it enables the bird to significantly increase its flight distances. A
seagull can save up to 70% of its energy while soaring. 24

Energy from Air Currents
Birds use air streams in different ways: A kestrel gliding down a hillside

or a seagull diving along coastal cliffs make use of airstreams, and this is
called "slope soaring".
When a strong wind passes over a hilltop, it forms waves of motionless
air. Birds can soar on these waves as well. The gannet and many other

seabirds make use of these motionless waves created by islands. Sometimes
they use the currents generated by smaller obstacles such as ships, over
which seagulls soar.
Fronts generally create the currents providing uplift for birds.
Fronts are interfaces between air masses of different temperatures or
densities. The soaring of birds on these interfaces is referred to as "gust

gliding". These fronts, which are especially formed at coasts by air currents
coming from the sea, have been discovered by means of radar, through the
observation of sea birds in flocks gliding in them. Two other kinds of soaring
are known as thermal soaring and dynamic soaring.