Emperor penguin air sac oxygen

Some marine birds and mammals can perform dives of extraordinary duration
and depth. Such dive performance is dependent on many factors, including
total body oxygen (O2) stores. For diving penguins, the respiratory system
(air sacs and lungs) constitutes 30-50% of the total body O2 store. To
better understand the role and mechanism of parabronchial ventilation and
O2 utilization in penguins both on the surface and during the dive, we
examined air sac partial pressures of O2 (PO2) in emperor penguins
(Aptenodytes forsteri) equipped with backpack PO2 recorders. Cervical air
sac PO2s at rest were lower than in other birds, while the cervical air
sac to posterior thoracic air sac PO2 difference was larger. Pre-dive
cervical air sac PO2s were often greater than those at rest, but had a
wide range and were not significantly different from those at rest. The
maximum respiratory O2 store and total body O2 stores calculated with
representative anterior and posterior air sac PO2 data did not differ from
prior estimates. The mean calculated anterior air sac O2 depletion rate
for dives up to 11 min was approximately one-tenth that of the posterior
air sacs.  Low cervical air sac PO2s at rest may be secondary to
a low ratio of parabronchial ventilation to parabronchial blood O2
extraction. During dives, overlap of simultaneously recorded cervical and
posterior thoracic air sac PO2 profiles supported the concept of
maintenance of parabronchial ventilation during a dive by air movement
through the lungs.