BIRD MIGRATION

Timaru Herald, Volume CXLIII, Issue 20926, 4 January 1938, Page 3

BIRD MIGRATION

THE WHYS AND WHEREFORES SCIENTISTS PUZZLED Any day in September you may loot up from your gardening or youi country walk and see the swallow: going to Africa, writes R. S. R. Fitter in the "News-Chronicle,” London. If you are near the sea, especially on the east or west coasts, you maj see a steady stream of swallows, martins and other birds flying in ones anc twos, and in small parties of 10 or 2( or 50. southward toward the sun. If you are very lucky indeed, yot may chance to see a real mass migration passing overhead, countless thousands of birds streaming across the sky for six or seven hours or more. What is the cause of this strange instinct of migration, that makes millions of birds leave their summei homes in the north in the autumn anc spend the winter in warmer climates near the Equator? For centuries men have puzzled ovei it. Aristotle devoted much space t( describing it. In the Bible the prophei Jeremiah wrote: "Yea, the stork in tht heaven knoweth her appointed times, and the turtle and the crane and the swallow observe the time of their coming.” Nearly 2000 years ago Gilbert White the famous author of "The Natura History of Selborne,” was still puzzled He thought swallows hibernated in the winter, like dormice and butterflies and found it hard to believe that suet small birds as swallows and warbler? could travel several thousand miles tc and from Africa every year. Another learned man of the eighteenth century suggested that migrating birds probably went to the moon! An equally strange idea was the old country belief that the black-faced geese, turned into barnacles for part of the year. To-day, though the scientists are beginning to know where, they do not yet know exactly why birds migrate.

Bird-ringing schemes, worked by fixing numbered aluminium rings on to one of the bird’s feet, have proved beyond a shadow of a doubt that many birds which build their nests in England are to be found in Africa in the winter, and that many birds which build their nests in Northern Europe in the summer spend the other six months of the year in the British Isles. In December, 1912, the first swallow ringed in England was recovered in Natal, South Africa, and only a few years ago the first British-ringed cuckoo was reported from the West Coast of Africa.

Experiments that have been carried out in Germany and Britain and America, indicate that the migration instinct is a seasonal one which operates only for a limited period in the spring and autumn. Migratory birds have been kept in cages at the time when they would normally have been migrating, and they have been seen to be possessed by

r. kind of restless fever at this time. I their wings quivering with an evident ! anxiety to be gone. Afterward, they | have been released and have shown no I desire at all to migrate, even in the i coldest weather. I This and other experiments lead I scientists to suppose that the migraj tory instinct is something quite indeI pendent of weather conditions, available food supplies, and the breeding instinct, which have hitherto been | supposed to be main causes of migrai tion. Much more work will have to be done, however, before we shall be able to say that we know how the instinct really does work.