A bird’s wing has evolved over millions of
years. There is a large muscle mass close
to the body that supplies the power strokes
for flapping, smaller muscles along the wing
that control the primary flight feathers at the
wingtips, and the secondary flight feathers
at the rear or ‘trailing edge’ of the wing.

Primary flight feathers

The feathers at the wing

tip and outer edge of

the wing provide the

majority of the thrust.

They can also be

separated and rotated

so that they don’t cause

negative thrust when

the wing is in the

upward stroke of

a flap.