Work in groups of four. Take turn with your members to read the text entitled How Do Birds Fly? with correct intonation and pronunciation. Then answer the questions.

How Do Birds Fly?
By Rachael Bell, Victoria

    All birds have wings and although not all birds can fly (penguins and kiwis for example), wings are essential for flight. Flight requires the momentum of lift. An aeroplane acquires lift by using its wings and the forward thrust created by jet engines and propellers. Birds obviously lack propellers, but use their wings and the air that moves around them to create lift. Like an aerofoil, bird's wings are not flat - they are concave - and this encourages air to flow faster around them. To enable flight, birds change the shape, direction and the movement of their wings.

    When birds such as pigeons, for example, move their wings in an up and down fashion, lift is created when fast moving air passes over the upper surface of the wing quicker than the air underneath it. The slower air under the bird's wing pushes under the wing with far greater force than that above it, thus creating lift. To increase the amount of lift needed, birds clap their wings together and this speeds up the flow of air around the wing. As bird's wings move in this way, spirals of air, known as vortices, are created.

    Like birds themselves, birds' wings vary in shape and size. Some birds have long narrow wings others have short broad wings and such variety produces different types of flight. When out at sea, albatrosses, with their long narrow wings, make use of changes in wind direction to soar (dynamic soaring) in flight above the surface of the water. Long wings such as these are harder to flap, but are ideal for soaring and are invaluable for the albatrosses lifestyle. Starlings have much smaller, shorter wings that produce flapping flight. These wings are less efficient for gliding or soaring flight, but are ideal for short bursts of energetic flight.

Taken from: www.rspb.org.uklbi rds-and-wildlife/bird-and-wildl ife·guides/ask-an-expertlpreviouslbirdsjly. aspx

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