How do birds fly in a seemingly straight line instead of up and down when they flap their wings?

Question

How do birds fly in a seemingly straight line instead of up and down when they flap their wings?

In: Other

Answer 1

For lack of a better way to put it, their shoulder joints rotate as their wings flap – while it’s imperceptible in real-time, they’re not necessarily getting a full “loft” from a downflap, as the shoulder rotates to reduce force on the wings.