Cervical air sac oxygen profiles in diving emperor penguins: parabronchial ventilation and the respiratory 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 (P_O ) in emperor penguins (Aptenodytes forsteri) equipped with backpack P_O  recorders. Cervical air sac P_O  values at rest were lower than in other birds, while the cervical air sac to posterior thoracic air sac P_O  difference was larger. Pre-dive cervical air sac P_O  values 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 P_O  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 P_O  values 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 P_O  profiles supported the concept of maintenance of parabronchial ventilation during a dive by air movement through the lungs.