The stoichiometric approach in determining total evaporative water loss and the relationship between evaporative and non-evaporative heat loss in two resting bird species: passerine and non-passerine

Background Evaporation is of significant ecological interest. Evaporation from an animal always results in a decrease in the temperature of the surface from which the evaporation occurs. Therefore, evaporation is a one-way transfer which causes heat loss from the organism. Biological evaporation always involves the loss of water which is a vital resource for nearly all biochemical processes. Evaporation is loss of heat via loss of body mass.

Methods The simultaneous determination of energy expenditure and loss of body mass in resting birds allows us to estimate evaporative heat loss. This method includes direct measurements of the energetic equivalent of the loss of body mass as the ratio between heat production, determined by the rate of oxygen consumption and the loss of body mass at various ambient temperatures.

Results The data indicate that evaporation was minimal at lower critical temperature and that the rate of evaporation increased at lower or higher temperatures. Obtained results indicate that passerine and non-passerine species have the ability to change their non-evaporative heat conductance the same number of times (approximately fourfold), and that their abilities in this respect are similar.

Conclusions The novelty of the study resides in the stoichiometric approach to determination of total evaporative water loss. The analysis shows that determinations by stoichiometric approach of total evaporative water loss yielded the values, which fit into the confidence intervals of all equations from literatures. The basal metabolic rate and non-evaporative thermal conductance are fundamental parameters of energetics and determine the level of physiological organization of an endothermic animal.