DIFFERENTIAL AIR SAC PRESSURES IN DIVING TUFTED DUCKS AYTHYA-FULIGULA

The air in the respiratory system of diving birds contains a large pro portion of the body oxygen stores, but it must be in the lungs for gas exchange with blood to occur. To test the hypothesis that locomotion induces mixing of air sac air with lung air during dives, we measured differential pressures between the interclavicular and posterior thora cic air sacs in five diving tufted ducks Aythya fuligula. The peak dif ferential pressure between posterior thoracic and interclavicular air sacs, 0.49 +/- 0.13 kPa (mean +/- S.D.), varied substantially during u nderwater paddling as indicated by gastrocnemius muscle activity. Thes e data support the hypothesis that locomotion, perhaps through associa ted abdominal muscle activity, intermittently compresses the posterior air sacs more than the anterior ones. The result is differential pres sure fluctuations that might induce the movement of air between air sa cs and through the lungs during dives.