Here to return to
PREPARING FOR THE JOURNEY
ALTHOUGH the bird traveler has no trunk to pack, guidebook to study, nor ticket to buy, still he must make some preparations for the journey.
The Warbler which nests in Alaska and passes the winter in northern South America, should not begin a seven-thousand-mile voyage through the air, over mountains, plains, and seas unless its engine is in good order and it has a proper supply of fuel.
“But,” you ask, “what is a bird’s engine and where does it carry fuel?” A bird’s engine is really its wings and the muscles which move them. It is one of the most perfect engines in the world. It is simple but strong. It works easily but is powerful, and it rarely gets out of order.
For many years man tried to make flying-machines which would have wings like those of birds. But he never succeeded. He could not make even a feather! Finally he discovered that if he would make a machine that would fly, he must give it wings and an engine. So he constructed an aeroplane which has wide, stiff wings or planes measuring about thirty feet from tip to tip. These wings cannot be flapped, and, in themselves, they furnish no power. But to them man added an engine driven by gasoline and electricity. This engine turns a long-bladed propeller which urges the aeroplane forward, while the planes support it when it is in motion. But a bird’s wing, we must remember, is both plane and engine. It gives support as well as power. It is therefore a far more remarkable machine than the one made by man.
Now let us see some kinds of birds’ engines. Although they all work on the same principle they differ greatly in shape and size. We shall find that most birds which make long journeys have one kind of engine, while those that travel but little have quite a different looking engine.
Think of the Swallow’s engine. It is quite as long as the bird itself; the feathers are stiff and strong, and when in motion they cut the air with graceful, sweeping strokes which send the bird forward easily but at great speed. A bird fitted with such an engine, we feel sure, could make a very long journey quickly and without tiring itself. So we find that the Barn Swallow, which glides and darts about our fields in summer, goes to Brazil to spend the winter.
THE SWALLOW’S ENGINE.
The long wing and small foot of a Swallow, a bird that travels
and feeds in the air.
Now let us see the engine of the Quail or Bobwhite. How short and round it is! And when the bird flies how rapidly it moves its wings—at least four times as fast as does the Swallow! The bird is so heavy, its wings so small that, although it can go swiftly, it is evidently hard work for it to do so. It therefore makes but a short flight and soon drops to the ground again. So we are not surprised to find that Bobwhite spends his life near the place where he was born. He is no traveler. Most of the time he lives on the ground like a chicken.
The short wing and large foot of Bobwhite, a bird that stays
at home and feeds on the ground.
And like a chicken he has large, strong feet, which not only carry him about from field to field in search of food, but can be used to scratch for it. He needs his engine chiefly to help him to escape quickly from some prowling fox or other enemy. He must go fast if not far.
If we should put Bobwhite on an island where there were no enemies to escape from and where it was never necessary for him to fly, he might, in time, wholly lose the use of his engine and be unable to fly. Indeed this has happened to some birds of the Rail and Gallinule family. They have lived so long on islands, where they never had to fly, that their wings have become too small to raise them in the air. It is as though their engines had become rusty from disuse.
Not all the great bird travelers have such a splendid engine as the Swallow. Some, indeed, like the Sora or Carolina Rail, have such small wings that it is difficult to understand how they fly from Canada to South America. But we must remember that their bodies are light. It is not so much the size of the engine as the size of the train it draws that counts. The Hummingbird’s wings are not much wider and longer than one’s thumb, but they are large enough to carry the bird’s tiny body over thousands of miles.
Everyone knows that birds’ wings, or engines, are made of feathers growing from a very light but wonderfully strong frame of bones. Lightness and strength are indeed the main features of the bird’s wing. But even the strongest feathers wear out. Then the engine must be repaired. No bird wears a suit of feathers longer than one year. The change is usually made in summer after the family has left the nest and learned to take care of itself. Then the old and worn feathers drop out and fresh ones grow rapidly in their places. This is called molting.
If the feathers should fall out of one wing faster than they did from the other, the bird’s flight would be unbalanced. It would be crippled, like an aeroplane with only one plane. Or if all the feathers were to fall out of both wings at once, the engine would be powerless. The bird could not get its food and it might fall a prey to its enemies. To prevent this, the bird’s engines are repaired in the most wonderful way.
The feathers begin to drop from the middle of the wing; only two are lost at a time, and they are from exactly the same place in each wing. New ones at once sprout from the hole left by the falling feather. When they are about half grown, two more feathers are lost as before, one from each wing. These are probably the next feathers toward the outer ones. Again, the new ones sprout quickly. Now the third pair is lost; if the second pair fell from toward the outermost feathers, the third pair will fall from toward the body, or the innermost ones.
So the repair of the engine, or molt of the wings, continues. First a pair of quills from the outer half, then a pair from the inner. The process is slow, for it waits on the growth of the new feathers. But it never robs the engine of its power. At no time is there more than a pair of feathers missing from both wings. The wing is therefore always balanced and the bird can fly during the entire molt.
The molt does more than repair the engine. It may also disguise the bird traveler so that he can journey more safely. I say “he” because if a disguise is used at all, it is worn only by the male.
The brilliant male Scarlet Tanager replaces his fiery red body feathers with others of olive-green, like those of his mate, his wings and tail remaining black.
The Bobolink, as we shall see beyond, changes his costume of black, white and buff for an inconspicuous suit like that of his wife. Many other birds follow this custom. Why should they expose themselves to danger by wearing gay colors when traveling? Or, at any rate, why should they don their courtship dress until the return of the wedding season the following Spring?
It is not until the molt is completed and the engine is in perfect order that the bird starts on its travels.
It only remains now to take the fuel aboard. This with birds is nothing less than fat. A runner training for a race tries to become thin. But many birds when preparing for a long journey put on a coat of fat. On it they live, to a greater or less extent, during the time of migration. If the bird can get food by the way, it is not necessary to carry so much with him. Swallows can feed as they fly. The Warblers and Vireos and other birds that fly by night can hunt insects during the day. But the Plover and other birds that travel over the seas cannot stop for meals. Like bears in winter they must live on themselves, that is, on their fat. When they start, their body is covered with a thick layer of fat, but when they arrive at their journey’s end it has disappeared. It was fuel for the engine.
Even the birds that travel overland, where food is plentiful, take some fuel with them. I have noticed when collecting and preserving specimens of birds in South America in the spring for the American Museum, that all the North American birds which were about to start on the long journey to their summer homes were very fat, while all the native birds, which were getting ready to nest, were practically without fat.
Still, there they
were, living together; eating, probably, much the same kinds of food. Why this
food should make one bird fat and the other thin it is difficult to say. But we
may be sure that in each case it was preparing the bird for the work it had to
SUGGESTIONS FOR STUDY
Compare a bird with an aëroplane. How does a bird’s flight differ from that of an aëroplane? Mention some of the birds you know and describe the shape and relative size of their wings. Are they long and pointed; short and rounded; large or small? Are they for long journeys or short ones? Count the number of wing strokes made by a flying bird in five seconds. Which makes the greatest number—long-winged birds or short-winged ones? What part does the bird’s tail play in flight?
What can you tell about the bones of a bird’s wing? Compare them with those of a man’s arm and hand. Name the kinds of feathers attached to the wing and from which part each set grow (a chicken’s wing might be obtained for this purpose). Name the parts of a feather. How are the feathers of the wing molted? What birds can you mention that wear differently colored costumes during the year? Compare their summer, with their winter dress. Do both male and female birds undergo this change in appearance? If the male differs from the female, which is the brighter? Why?