How wings work
Birds' wings are really front legs covered in feathers. But, unlike the front legs of other animals, they don't support the bird's weight on the ground.
One look at a bird’s skeleton shows how its wings, whilst having some similarities to our arms, are different to human arms. Wings are modified arms which are better adapted to flying.
But there are some important differences.
- The upper arm is short and thick, for powering the wing beat: this part is invisible on most birds.
- The bend in the middle of the wing is actually the bird’s wrist.
- The last joint of the wing is like our hand, but it has only one finger bone.
- This holds all the long primary feathers used for flying.
A bird’s wings are no use on the ground, so it folds them away neatly when it lands. You can see the main flight feathers folded on either side of its body.
On birds with longer wings, the tips of the primaries stick out near its tail. The bird’s ‘shoulders’ that appear either side of its breast are actually its wrists.
Getting a lift
Wings are much bigger than our arms, but being made mostly of feathers and hollow bones makes them very light. Their shape uses the wind to make flying easier.
From side on, you can see that a bird’s wing is flat underneath and curved on top. This means that the air passes faster above it than underneath it. The difference in air speed creates air pressure underneath the wing, which lifts it up. Aeroplane wings use exactly the same shape to help give them lift.
Flapping helps a bird to push itself through the air. On the downstroke, the wing forces the air down, pushing the bird up in the process.
At the same time, the wing tip tilts forward to push the air back. This pushes the bird forward. The upstroke raises the wings back into position for the next downstroke.
Flapping takes a lot of energy, and it is easier with smaller wings. Small birds, such as sparrows flap their wings in fast bursts. Larger birds, such as gulls, flap much more slowly and glide whenever they can.
A flying bird changes direction by altering the angle or shape of its wings.
By tilting one wing down it can turn towards that side. See how this works by making a paper plane and tilting one wing down.
To slow down or land, a bird fans out its tail and tilts its wings back to create more air resistance. Try tilting back the wings on your paper plane and see what happens.