system
Given the following post, respond as if you're commenting on Reddit:
human
Do high flying birds need less oxygen?

Do high flying birds need less oxygen in their breaths, or do they take breaths when they are lower altitudes (like whales surfacing for air)?
gpt
Birds have efficient lungs, they have air sacs connected to the lungs and oesophagus, when they breath their lungs and sacs get filled with oxygen and when they breath out the spent air in the lungs leaves and the sac air goes into the lungs giving them a double dose of oxygen.