Читать книгу Enid Blyton's Nature Lessons - Enid blyton - Страница 6
ОглавлениеMIGRATION
“There’s a north-east wind coming over the hill,
The days are shorter, the nights are chill,
Come, little brothers, we must not stay,
Warblers, cuckoos, and swallows—away!”
You must often have wondered where the cuckoo suddenly appears from in spring, and where the swallows and martins go in the late summer and autumn. Why don’t they stay with us? Where do they fly? How do they know the way?
Perhaps you have seen swallows collecting together for their autumn migration. I have seen them in October in hundreds on the roofs of houses and along telegraph wires, sitting there like little notes of music.
What Migration is
We give the name “migration” to the big movements of birds from one place to another, chiefly the movements north to south in winter, and south to north in autumn. Many, many books have been written about these movements, many watchers have given their ideas about it and many answers have been made to the how, why, and wherefore questions of this mysterious journeying of birds. But the whole truth has not been found out yet, and even the cleverest men have to admit that they don’t really know the true explanations of bird migration—they can only guess at them.
MIGRATING SWALLOWS ATTRACTED BY A LIGHTHOUSE
In many instances the lighthouses have been equipped with perches on which the birds can rest.
Swallows, swifts, martins, cuckoos, and other birds leave our land for a warmer country in late summer or autumn. They go to the lands of Southern Europe, Egypt, and farther south into Africa, some of them travelling thousands of miles. Here they find plenty of insect life and warmth, but they do not nest and bring up young ones there. The swifts leave us very early indeed, when there are plenty of insects here and the weather is warm—so that to say these birds, at any rate, leave us because of the cold and scarcity of food is quite wrong. Then, again, you might say, Why do they leave the warm countries to come back to us again in the spring?
Most naturalists say that birds like to bring up their young ones in as cold a climate as they can, as then they are hardier and healthier—and that that is the reason why they migrate to cooler lands in the spring. Others say that it is an instinct from long ago which makes the birds fly to and fro in such a remarkable way—an instinct dating from the time when a great glacier forced its way slowly southwards from the Pole, and drove birds and other life before it. Each spring, when the weather was warmer, the birds returned as far north as they could—for they have a strong feeling for “home”—and so began the to and fro migration movement which has lasted down to the present time.
The Flight
I have said that once every year the birds fly to and fro, sometimes over thousands of miles of land and sea. I know the question that is on the tip of your tongue—How do they know the way? How does a swallow from Norfolk find its way to Africa, and then back again, maybe even to the very same roof?
Perhaps it remembers from last year, you say. Well, a bird has a marvellous memory, and if it made a journey once, it could probably make it again, recognising such things as shapes of land, lakes, rivers, and so on, on the way. But what about the young birds which have never made the journey before, and are only a few months old? How do they know?
That’s easy, you say; they go with the old ones and simply follow!
But the curious and wonderful thing is that they don’t! The young ones fly off by themselves, generally before the old ones, and, as far as naturalists can tell, they have no old birds with them as leaders.
Another curious thing is that many kinds of birds fly during the night when they cannot possibly see any landmarks, and can only be guided by two things—the wind and their own wonderful sense of direction. Maybe these two things together will be found some day to solve the mystery.
In spring, the birds fly northwards, or north-eastwards, with the warm, south-westerly spring wind behind them. This helps them along, and, perhaps, without its assistance many thousands of them would never reach “home.” In autumn, there is a chill north-easterly wind blowing, and this carries the birds in a south-westerly direction towards the warmer lands they need. So they certainly have a great help, as regards direction, in these two winds, but this would not alone explain the marvellous way birds have of finding their route.
Accidents
It is not every bird that comes safely from country to country. Many, many of the feathered travellers perish on the journey. If a storm blows up, or the wind miscarries, they may be blown out of their way, and, tired and lost, fall into the sea or down to the land, where they lie too tired to move if anyone approaches them.
Lighthouses are a great attraction to storm-bound birds. They seem to think they can find their way by beating against the lanterns, poor things! Lighthouse-keepers tell of hundreds and thousands of wretched little lost birds circling round and round the light, only to kill themselves against it at last.
Sometimes a steamer in mid-ocean will be descended upon by hundreds of little migrants, eager for a rest, or, perhaps, blown out of their way and lost. It is only the strongest, fittest, and luckiest that reach their journey’s end safely.
Some Interesting Facts
Most birds, when migrating, fly very high indeed—too high to be seen by our naked eyes. Probably there is a steady wind very high up which helps them considerably. Others fly low like a trail of smoke over the water. These, of course, cannot possibly see where they are going—they must trust to instinct for direction.
Some birds can fly sixty miles an hour to keep ahead of a storm, but they cannot keep that pace up for long. Usually thirty miles an hour, or thereabouts, is the speed chosen.
Young birds leave first, and old birds return first, except in the case of the cuckoos. The old cuckoos leave five or six weeks before the young cuckoos, and are gone very early in the year indeed.
So punctual is the arrival of bird migrants in some places, that it is almost possible to tell what month or week it is by the arrival of the different birds!
The autumn migration is not so hurried and urgent as the spring rush. Sometimes the route followed is simply a flight from one good feeding ground to another. At each, the birds rest and feed, and then go southwards once again. In spring, the birds eagerly long for the joys of nesting, and rush northwards as quickly as they can to their “home”—for where they bring their little ones up must surely be their homeland!
Partial Migrants and Birds of Passage
While some of the birds we call “resident” (that is, always with us), such as the rook, the song-thrush, and the lark, do remain with us all the year round, others of the same kind go south in the autumn, though never very far beyond our isles, and return in the spring. These birds are called partial migrants, as they do not all migrate.
There are also birds which fly over our land or down our coasts, on their way from north to south, or south to north, and do not, save by accident, or for the purpose of resting a little, visit us. These are called birds of passage. When you read in the newspaper about some unusual bird being found in one of our counties, you may be sure it is either a bird of passage or a casual visitor which has come to us by mistake.
QUESTIONS TO ANSWER AND THINGS TO DO
(1)
Why do the birds fly away from us in autumn?
(2)
What helps them very much on their journey?
(3)
Put down the names of some that go, and some that stay with us for the winter.
(4)
Draw some straight lines for telegraph wires and then see if you can put some little swallows on them.
(5)
Remember to listen for the returning cuckoo next spring, and tell your teacher the date on which you heard it.
