Question

Explain the difference in the process of respiration in birds when flying and when not flying?

Answer 1

When they fly, the process is passive.

Explanation:

When not flying, the birds breath just like humans do. Active inhale, passive exhale. Nothing new.

But they have 9 air sacs anchored to their wings, so when they fly they force air in and out of the sacs due to volume modifications.

If you've ever stayed near a bird and heard the sounds coming from its nose synchronise with the movement of its wings, now you know what's the reason behind that.

Also, those sacs maximize the pulmonary total volume, as they need a lot of oxygen when flying.