Bird migration is a fascinating phenomenon that has intrigued humans for centuries. The picture is now becoming clearer on how these creatures get from colder climates to more temperate climates every year.
According to an article by Charles Walcott, Professor, Neurobiology and Behavior, Cornell University, and former director, Cornell Laboratory of Ornithology, it is through a combination of:
1) sighting features like rivers, coastlines, and mountain ranges;
2) monitoring the Earth's magnetic field (apparently using not only their visual system but also tiny grains of a mineral called magnetite in their heads);
3) they observe the stars and use the sun for guidance;
4) smell;
5) probably by simply following their neighbors as large flocks migrate. It is thought that, at least in some birds, they have a way to overcome the problem of true north vs. magnetic north deviations. This is believed to be done by recalibrating their internal magnetic compass with star navigation during rest stops. If the rest stops aren't long enough the birds get lost.
Different types of flying techniques also play a major role in the migration of birds. The most basic being the technique of flapping and flying until they reach their destination. It is used by geese and many other birds.
Some birds such as hawks and vultures will "soar" by using thermals. Thermals are updrafts caused by solar heating. Since the thermals are present only during daylight hours and commonly over relatively level terrain, it leads to huge concentrations of migrating birds.
There are also birds that will flap their wings long enough to gain altitude then glide until they need to gain altitude again.
Other birds will flap their wings long enough to gain altitude then fold their wings to go into a closed wing glide. These are birds whose wings would create to much drag if left unfolded.
Happy birding!
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