Movements in birds

Birds

Sparrow, crow, pigeon, parrot, eagle, hen, duck, swan, ove and peacock, are all birds. Birds walk on the ground and igh also fly in air. Some birds (like duck and swan) also swim in my water. Birds walk on the ground by using their hind limbs (see Figure 18). Those birds which swim in water do so by raig pushing against water with their hind limbs which have d trio webbed feet. The webbed feet help the bird in swimming in water.

The birds can fly because their bodies are adapted (or modified) for this purpose. The main adaptations which have been made in the bodies of birds by nature to enable them to fly are the following:

Their forelimbs are modified to form wings for flying.

Their flight feathers provide a large flat surface which is light but strong.

Their bones are hollow and light. Their bodies are streamlined and extremely light. They have powerful flight muscles. Their breastbone is extended (as keel) for the attachment of large flight muscles (which move the wings up and down).

In birds, the muscles for flying act on the wings. One pair of muscles pulls the wings down and the ther pair of muscles pulls the wings up. When a bird moves its wing down, it is called a 'downstroke'. And when the bird moves its wings up, then it is called an upstroke. The birds move their wings up and own quickly by the rapid contractions and relaxation of their flight muscles. We will now describe how a ird actually flies.

Birds fly by a constant flapping (up and down movement) of their wings. During the downstroke, me raised wings of a bird go down and back . When the wings go down, mey push the air down. The air pushes up the wings with an equal force which makes the bird go up.

The backward movement of wings pushes the air in backward direction. This air pushes the wings in the forward direction and makes the bird move forward. Thus, during the downstroke of wings, the air is pushed downwards and backwards. The equal and opposite reaction force of air pushes the bird up and forward, and makes it fly.

After making the downstroke, the wings must go back up to their starting position. During the upstroke, the bird brings its wings from the lowermost position to uppermost position so that it may repeat the downstroke to keep flying . While bringing the wings up during upstroke, the bird partly folds its wings so that the effect of air is reduced.

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