There is no specific name for this physiological feature of the kakapo. It is simply called an inflatable thoracic air sac.
alveoli
air sac
Kakapo is the Maori name. It means "night parrot".
the air sac itself.
it optain air by when it goes over water
The biological term for an air sac is alveolus. The plural is alveoli.
Carbon dioxide
The scientific name of the only remaining takahe, the South Island takahe, is Porphyrio hochstetteri.
An alveolus is a single air-sac, and alveoli are multiple air-sacs.
It is easy for air to pass across the wall of an air sac because the wall is thin.
Alveoli is an air passage
A air sac