I was completely mind blown when I found out so I decided to share it.

Birds get oxygen into their lungs both when they breathe in AND when they breathe out. This is necessary to meet the extremely high oxygen demand during flight.

They have air sacs near the lungs and overfill the lungs while they inhale so that the excess air goes into these air sacs. When they exhale the air sacs empty into the lungs reoxygenating the blood.

Bird anatomy - Wikipedia, the free encyclopedia

And we're stuck with this stupid one way breathing.