Man has always wondered how an animal finds its way from station to station along its route…
It is particularly difficult to find out why and how animal migration takes place exactly. Why does an animal depart from the place of its birth and later return? What determines the time of departure, the direction of the journey and its length?
Seeking answers to these questions, scientists have not only made numberless observations, but have also engaged in a vast amount of physiological research and other experimental work.
Numerous studies have revealed a relationship, for instance, between migration and weather. But this is not the whole story by any means. As investigators accumulate information, it is becoming increasingly clear that the migration of a given species is determined particularly by what can be normally expected, on the basis of the accumulated experience of many generations. Trying to solve this problem, investigators have even studied the effects of all the different elements of nature. So, let’s see…
The Extensive Migration of Birds
Of all land creatures, birds are the best equipped for extensive travel because of their wings. The geography of the earth seems to provide the impetus for their migratory urge. Great land areas in the upper half of the Northern hemisphere furnish abundant nesting sides, which rigorous winters make untenable. The long-distance migrators, therefore, are the birds that like cool weather, but not freezing weather.
Birds that nest in the warmer areas do not migrate. In the Southern Hemisphere, only the southern part of South America and the higher altitudes of the Andes have sufficient temperature changes to drive land birds toward warmer territorials.
Some birds can stand very cold weather. The gyrfalcon and the snowy owl only occasionally leave their Arctic homes. Many birds can endure freezing temperatures, provided that the periods of low temperatures are not too protracted. They move only far enough away from their homes to escape the worst rigors of winter. In general, birds that prey upon other birds and on small mammals can live through a northern winter and so can the large seedeaters. Most of the small insect eaters and seedeaters among birds migrate to territory that is not covered by snow.
The long-distance migration record of 22, 000 miles is held by the arctic tern. This graceful bird builds its nest on rocky or sandy coasts, often around the Arctic Ocean and occasionally to within eight degrees of the pole. Arctic terns nesting along northern Greenland spend less than four months there. Then they fly eastward to northern Europe and southward along the coast to Africa. Some fly down the African continent to its very tip and then make their way to the Antarctic gardens. Others cross over to Brazil from northern Africa. They fly down the South American coast and from there to their Antarctic winter range. Certain arctic terns of North America have taken to nesting farther south along both coasts. Their trip is correspondingly shortened.
Another Arctic Circle bird, the golden plover builds its nest of reindeer moss in the wet tundras of Siberia, Canada and Alaska. In early fall, the golden plovers start their flight south. Those from eastern North America fly down the Atlantic to the pampas of South America. In the spring, they follow the Central American coast to Louisiana and thence up the Mississippi Valley to the identical breeding grounds they had left. Alaskan golden plovers migrate to Hawaii. Those from Siberia winter in various islands of the Indian Ocean and also in Australia and New Zealand.
To find more about birds’ migration, come back for part 3.