Measurement of evaporative water loss in small animals by dew-point hygrometry

This paper presents the procedures and equations to be utilized for measurement of evaporative water loss (mw), by use of the dew-point hygrometer, in small animals exposed to air containing water vapor in an open-flow system. The system accounted accurately for the water evaporated from a bubble flask. In addition, hygrometric measurements of pulmocutaneous mw in pigeons (Columba livia, mean mass 0.31 kg) agreed closely with simultaneous gravimetric measurements, utilizing a desiccant in the sample stream, in a manner independently of air temperature (Ta, 20 or 40 degrees C), ambient water vapor pressure (PW, 4–16 10(2) Pa), or mw (5–66 mg-min-1). Evaporation in pigeons was independent of PW at 20 degrees C, but increased with decreasing PW at 40 degrees C, suggesting differences in ventilatory adjustments to changes in PW at the two temperatures.