I’m going to have to dive into this further at some point. I knew the air sacs existed, but not how they worked. From some more quick reading, birds breathe very differently than we do.

BirdFact

The avian respiratory cycle can be described in four stages, or two inspirations and two expirations, which is very different from our two-stage tidal respiration pathway. Here’s how it works:

When birds inhale, air collects in the posterior air sacs below and behind the lungs. This oxygenated air only enters the lungs when they exhale, and that’s when the bulk of gas exchange occurs. On the next inspiration, deoxygenated air leaves the lungs and enters the anterior air sacs. Finally, air is expelled through the beak on the second exhalation.

Mika Steele

The Great Horned Owl gets oxygen by in taking through its mouth. In addition to lungs, owls also have air sacs. Air sacs are vital for these owls. When owls fly, they burn a lot of calories, so they have to take in a lot of air. The air sacs act as extra room to store oxygen. Oxygen enters the blood through diffusion this is when the cells diffuse so molecules move from higher concentration to lower concentration. Because birds don’t have diaphragms, air is moved in and out through pressure changes in the air sacs. Unlike mammals, the owl’s lungs to not expand and contract. Birds exhale carbon dioxide, like all other animals.