Sunday, December 17

Bird Migration

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The secret of Bird Migration

 Have you watched the v shaped flocks of geese or ducks flying in the autumn sky?  Or waited for swallows to return to their old nests in spring? Man has always observed the autumn gatherings of birds, their departure for unknown land and the spring return, but for long time we were unable to explain the bird strange behavior. And many things about migration still remain a mystery.

Migrating birds are fascinating to watch where the tiny creatures get the strength for such long flights. How do they take their bearings? What makes them undertake such long trips? Today thanks to observation over many years and the marking of birds by ringing some of these questions can answer at least in part.

Why

The regular migration of birds is undoubtedly due to seasonal changes. Some species of birds nest in sparing in the north in the tundra. But conditions there are unsuitable for them all the year round. Even in warmer temperate regions bird that feed mainly on in sects cannot find enough food in the winter so they have to move to even warmer areas

When

In the northern hemisphere most migratory birds fly south before winter comes and the opposite occurs in the southern hemisphere. Migrations begin at a time when noting seems to hint that winter is near ,at least fist sight it is not changers in the weather that make  migratory birds flock together, become restless and get ready for departure, but changers in the length of the leave at roughly the same time every year, Whatever the weather.

How far

Amazing distance is covered by birds during their migratory flights. Small songbirds commonly fly from central Europe across the Alps. The Mediterranean Sea and the Sahara to central Africa .Storks regularly fly from Europe to southern Africa. The greater distance covered by the artic tern. It nests in the northern part of North America and Europe. But it over winter in southern reaches of Atlantic, Pacific and Indian oceans.  We can estimate from record of ringed birds that from their autumn departure from the nesting grounds to their return in spring. Terns often cover 40,000 km or more. That is equal to flying around the equator. It seems the only restriction to their migration is the size of our planet.

             The speed of bird flying is also remarkable .songbird usually fly at 50 km per hour. But radar has registered speeds of up to 160 km per hour in flocks of sandpipers and sand plovers.

How High

Migrating birds are not daunted even by the world’s highest mountains. It is true that most species fly relatively low and avoid high mountains. But cranes geese and curlews for instance have been seen in the Himalayas at heights more than 6000 m above sea level. Mountaineers have watched the birds fly above the highest Himalayan peaks rising above 8000m.

How do they take their bearings?

How birds navigate during migration is not yet completely clear. There are theories that birds can sense the magnetic field of the earth. The rotation of the planet or radiation of heat from the worm zones of earth. But the commonly health theory is that navigation based on the sun and the stars. Bird’s migration during day time has been founded process a perfect memory for the position of sun in both their nesting and winter grounds. Birds which migrate at night orientate themselves very accurately to the position of the stars and constellations.

Experiments which released specially marked birds showed that right direction by flying in irregular semicircles and once they found it they set out on the right course to their destination. This ability is not learned but is an inborn instinct of the species that has been developed over millions of years.

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