Energetic cost of running and heat balance in a large bird, the rhea.

TAYLOR, C. RICHARD, RAZI DMI'EL, MICHAEL FEDAK, AND KNUT SCHMIDT-NIELSEN. Energetic cost of running and heat balance in a large bird, the rhea. Am. J. Physiol. 221(Z): 597-601. 1971.-The energetic cost of running in the rhea (Rhea americana), determined as oxygen consumption, increased linearly with increasing speed. Oxygen consumption (M, ml 02 g-1 hr-I) relative to running velocity (v, km hr-l) could be expressed by the linear equation: M = 0.34 v + 0.39. Within the limits of accuracy, this relationship was identical in experiments at air temperatures of 25, 35, and 43 C. This cost of running is about twice the predicted value for a quadrupedal mammal of the same size, a situation similar to that observed in another bipedal animal, man. Body temperature increased during running, and heat storage accounted for a major part of the heat balance. For example, 75% of the heat produced when birds ran for 20 min at 10 km hr-l and air temperature of 43 C was stored. Increased evaporation plays a minor role in the temperature regulation of the rhea during running.