Page 86 - The Miracle of Migration in Animals

THE MIRACLE OF MIGRATION IN ANIMALS

A B

Birds can cover long distances using less energy by using the currents of
air created when the ground surface heats up. Large birds like storks and
eagles give themselves up to the warm air spirals rising from the earth and
glider.(A) Seabirds like the albatross and storm petrel gain speed and then
let themselves go with the air currents.(B)

to south. At the same time, the migrating birds can also glide in the
thermals that rise from different parts of the Earth’s surface. It is esti-
mated that if a broad-winged falcon were to flap its wings in flight, it
would use up its accumulated 100 grams (3.5 ounces) of pre-migra-
tory fat in just five days. But by using a thermal’s upwardly spiraling
air currents to gain altitude before gliding to the next thermal, that
same fat deposit can last 20 days—enough to provide the energy
needed for the journey of approximately 5,000 kilometers (3,000
miles) the birds make from the Neotropics.
Using the thermals that form when the ground heats up, some
migrating birds travel to very distant places. Spiraling in these invisi-
ble elevators, storks, cranes and pelicans can gain enough altitude to
glide hundreds of meters, hardly flapping their wings at all. Since

they can usually find another thermal at the end of their glide, they
can fly between continents while expending a minimum of energy.

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