Air sac temperature and acid-base balance during thermal panting in ducks.

Ducks become slightly hyperthermic at ambient temperatures (TA) above 35 degrees C, as indicated by cloacal temperature measurements. The air sacs do not represent important sites of evaporation, since their wall and air temperatures are not lower than ambient and body (cloacal) temperatures during thermal panting. Upon exposure to moderate heat loads (TA = 35 degrees C), arterial PO2 and PCO2 are relatively constant, whereas pH increases slightly. During exposure to heavy heat loads (TA = 42 degrees C), however, ducks become alkalotic, as indicated by a significant increase in arterial pH.