[KineticLensman]

Birds have all sorts of optimizations that improve efficiency, some of which make them very different from mammals. Their lungs are different from ours in two respects. Firstly, they are relatively rigid and the pumping is done primarily by separate air sacs. Secondly, they have an outlet pipe so can take in new air while also expelling the old. The result is continuous oxygen exchange rather than a breathing-in/breathing-out cycle like mammals.

You can see the effect in how prey is eaten after a hunt. A mammalian sprint-predator like a cheetah has to catch its breath before eating what it has just caught. Its avian equivalent, like a Peregrine falcon, can immediately start eating.

[jibal]

They improve efficiency in their airborne and tree crown niches, whereas mammalian traits are optimized for their respective terrestrial or aquatic niches. And so on and so forth for every species.