The
But only when the wind is blowing.
If the wind eases to less than about 16 knots ( 30 km
per hour) the albatross cannot soar. And while its long,
albatrosses are incapable of sustained flapping flight, this
means that when the wind abates, the albatross is forced
down and must rest on the ocean surface until the wind picks
up again.
It’s no coincidence, then, that albatrosses tend to be found
in the exceptionally windy southern latitudes of the ‘Roaring
Forties and Furious Fifties’, from Antarctica to South Africa,
Australia, and South America. In the North Pacific, albatrosses can be found traversing the ocean expanses stretching
from Hawaii to Japan, Alaska, and California. Equatorial seas,
with their famous low-wind ‘Doldrums’, are devoid of albatrosses—an exception being the area around the Galápagos
Islands, where winds are stronger thanks to the influence of
the cool waters of the Humboldt Current.
In Samuel Taylor Coleridge’s famous 1798 epic, The Rime
of the Ancyent Marinere, the sailor who killed the albatross
is on board a becalmed sailing ship. Since albatrosses can’t
survive where there is no wind, the dead bird around his neck
would seem an apt metaphor. But give an albatross more than
an average sea breeze, and its mastery of the air above the
waves is supreme.
master aviator of the ocean winds
Researchers, hoping to one day emulate the albatross’s
prowess in the flight of drones and other Unmanned Aerial
Vehicles (UAVs), have been steadily peeling back the
mysteries of how this avian aviator so adroitly uses the ocean
winds to power its flights. The albatross is a master of what
is now known as dynamic soaring, whereby this remarkable
bird uses differential wind speeds (‘wind shear’) near the
surface of the ocean to extract energy from the wind. 4
Exploiting the wind shear zone
As every student of flight and air movement knows, the
bottom-most layer of wind blowing above any surface,
including water, will incur friction and thus slow down. This
layer itself then becomes an obstacle that in like manner but
to a lesser extent slows the layer of wind immediately above,
which in turn somewhat slows the layer above it, and so on.
Thus at 20 metres altitude, the wind will be significantly
stronger than at sea level, with a gradient of intermediate
windspeeds in between. It is this 10- to 20-metre–high wind
shear zone above the sea surface that the albatross exploits to
power its flight.
There are four easily-discernible phases in each flight
cycle. First, a windward climb, then a curve from windward
to leeward (i.e. downwind) at peak altitude, then a leeward
descent, and finally a reverse turn close to the sea surface
that leads seamlessly into the windward climb of the next
cycle. The albatross does not flap its wings during any of
these phases; in fact its wings are firmly held in outstretched
position by a shoulder-lock system that allows the albatross
to keep its wings open without any muscular expenditure.
(The albatross shares this feature with the giant petrels—see
box: The albatross and the Ark.) The only muscular effort
expended is in controlling the turns.
The key as to how dynamic soaring permits sustained
flight is in the albatross’s change in direction. During the
first phase when facing windward, the albatross loses much
of its energy to drag and converts the rest into gravitational
potential energy as it climbs. The energy gain comes at the
highest point of the flight cycle as the albatross turns leeward.
As it glides downwind, the wind exerts a propulsive effect
throughout the descent which gives the albatross a maximum
total energy near the base of the descent. When turning
back from leeward to windward the albatross will inevitably
