How Birds Fly
O convince the children that a bird's wings correspond to our arms, they should see a fowl with its feathers off, prepared for market or oven, and they will infer the fact at once.
The bird flies by lifting itself through pressing down upon the air with its wings. There are several experiments which are needed to make the child understand this. It is difficult for children to conceive that the air is really anything, because they cannot see it; so the first experiment should be to show that the air is something we can push against or that pushes against us. Strike the air with a fan and we feel there is something which the fan pushes; we feel the wind when it is blowing and it is very difficult for us to walk against a hard wind. If we hold an open umbrella in the hand while we jump from a step we feel buoyed up because the umbrella presses down upon the air. The bird presses down upon the air with the wings, just as the open umbrella does. The bird flies by pressing down upon the air with its wings just as a boy jumps high by pressing down with his hands on his vaulting pole.
Study wing and note: (a) That the wings open and close at the will of the bird. (b) That the feathers open and shut on each other like a fan. (c) When the wing is open the wing quills overlap, so that the air cannot pass through them. (d) When the wing is open it is curved so that it is more efficient, for the same reason that an umbrella presses harder against the atmosphere when it is open than when it is broken by the wind and turned wrong side out.
A wing feather has the barbs on the front edge lying almost parallel to the quill while those on the hind edge come off at a wide angle. The reason for this is easy to see, for this feather has to cut the air as the bird flies; and if the barbs on the front side were like those of the other side they would be torn apart by the wind. The barbs on the hind side of the feather form a strong, close web so as to press down on the air and not let it through. The wing quill is curved; the convex side is up and the concave side below during flight. The concave side, like the umbrella, catches more air than the upper side; the down stroke of the wing is forward and down; while on the up stroke, as the wing is lifted, it bends at the joint like a fan turned sidewise, and offers less surface to resist the air. Thus, the up stroke does not push the bird down.
Observations should be made on the use of the bird's tail in flight. The hen spreads her tail like a fan when she flies to the top of the fence; the robin does likewise when in flight. The fact that the tail is used as a rudder to guide the bird in flight, as well as to give more surface for pressing down upon the air, is hard for the younger pupils to understand, and perhaps can be best taught by watching the erratic unbalanced flight of young birds whose tail feathers are not yet grown.
The tail feather differs from the wing feather in that the quill is not curved, and the barbs on each side are of about equal length and lie at about the same angle on each side the quill. See Fig. p. 28.
References—The Bird Book, Eckstorm, pp. 75-92; Story of the Birds, Baskett, pp. 171-176; Bird Life, Chapman, p. 18; The Bird, Beebe, Ch. XIII; First Book of Birds, Miller.
How Birds Fly
Leading thought—A bird flies by pressing down upon the air with its wings, which are made especially for this purpose. The bird's tail acts as a rudder during flight.
Method—The hen, it is hoped, will by this time be tame enough so that the teacher may spread open her wings for the children to see. In addition, have a detached wing of a fowl such as are used in farm houses instead of a whisk-broom.
1. Do you think a bird's wings correspond to our arms? If so why?
2. Why do birds flap their wings when they start to fly?
3. Can you press against the air with a fan?
4. Why do you jump so high with a vaulting pole? Do you think the bird uses the air as you use the pole?
5. How are the feathers arranged on the wing so that the bird can use it to press down on the air?
6. If you carry an umbrella on a windy morning, which catches more wind, the under or the top side? Why is this? Does the curved surface of the wing act in the same way?
7. Take a wing feather. Are the barbs as long on one side of the quill as on the other? Do they lie at the same angle from the quill on both sides? If not why?
8. Which side of the quill lies on the outer side and which on the inner side of the wing?
9. Is the quill of the feather curved?
10. Which side is uppermost in the wing, the convex or the concave side? Take a quill in one hand and press the tip against the other. Which way does it bend easiest, toward the convex or the concave side? What has this to do with the flight of the bird?
11. If the bird flies by pressing the wings against the air on the down stroke, why does it not push itself downward with its wings on the up stroke?
12. What is the shape and arrangement of the feathers so as to avoid pushing the bird back to earth when it lifts its wings?
13. Why do you have a rudder to a boat?
14. Do you think a bird could sail through the air without something to steer with? What is the bird's rudder?
15. Have you ever seen a young bird whose tail is not yet grown, try to fly? If so, how did it act?
16. Does the hen when she flies keep the tail closed or open like a fan?
17. Compare a tail feather with a wing feather and describe the difference.