Page 86 - The Miracle of Migration in Animals
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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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