Page 85 - The Miracle of Migration in Animals
P. 85

HARUN YAHYA


                    Utilizing the Wind in Flight


                    Radar research conducted during both spring and autumn mi-
                grations has shown that the weather and in particular, heat, plays an
                important part in a bird’s decision as to when to start migrating.
                Wind is one important factor influencing the start of flight. In spring,
                they are the winds blowing from the south and from the north in au-

                tumn. Clear weather conditions that let birds easily determine their
                route from the sky is a second important factor.
                    For gliders like the falcon, the osprey, the eagle and the vulture,
                proper wind conditions are essential. For falcons that migrate along
                the mountains in the eastern United States, the second day after the
                passing of a cold front is ideal, since steady northwesterly-west
                winds lift the gliding birds above the mountain ridges that run north

                                                        Birds that are heavy in rela-
                                                        tion to their wing span (such
                                                        as swans and ducks) must
                                                        flap their wings constantly,
                                                        using five times more en-
                                                        ergy than gliding birds.


                                                        This technique used by large
                                                        birds such as cranes and
                                                        birds of prey lets them
                                                        switch over at the peak from
                                                        flapping their wings to glid-
                                                        ing.

                                                        Small birds like wood war-
                                                        blers and fieldfares fly by al-
                                                        ternating between flapping
                                                        their wings and holding
                                                        them in. This lets them co-
                                                        ver distances by dropping
                                                        down and then rising again.




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