The Influence of Body Mass on the Endurance to Restrained Submergence in the Pekin Duck

Pekin ducks, ranging in mass from 0·05 to 3·5 kg, were force-dived to determine the maximum tolerance to diving asphyxia. The size of the respiratory and blood oxygen storage compartments and oxygen utilization during the dive were also measured. By the end of a maximum dive, less than 4% of the original O₂ store remained in the blood, whereas almost 25% remained in the respiratory system. In contrast, the level of arterial glucose did not change significantly during diving.

The relationship of a number of measured variables to body mass was analysed using linear regression analysis on log₁₀-transformed variables to generate power equations of the form Y = aX^b (Y, any variable; X, body mass; a, mass coefficient; b, mass exponent). The mass exponent was 1·19 for the total oxygen stores and 0·64 for maximum diving duration. Using measurements of brain and heart mass and literature estimates of the scaling of O₂ consumption, it was also possible to predict a mass exponent aerobic metabolism by these organs during a maximum dive. Allometric cancellation of mass exponents for O₂ availability and predicted utilization resulted in a residual mass exponent almost identical to the measured value for maximum dive duration. Thus it is possible to predict the relationship of maximum underwater endurance to body mass in Pekin ducks from a knowledge of the oxygen consumption by, and availability to, the central aerobic organs.