Total Evaporative Water Loss in Birds at Different Ambient Temperatures: Allometricand Stoichiometric Approaches

摘要

Total evaporative water loss ( )in Passeriformes and Non-Passeriformes was estimated by simultaneous measurements ofenergy expenditure and mass loss in resting birds. It was found that the percentage ofheat dissipated by water evaporation depends on body size. Published data for 102 birdspecies were analyzed together with my own measurements for 157 bird species at thermallyneutral temperatures (mostly 25°C) to establish the following relationship between and body mass: 25°C Aves = 0.28m , = 0.92, where isin g H O/day and m is body mass ( ). The scaling exponent 0.701 ± 0.007is 0.05 greater than for the relationship of basal metabolic rate ( )to body mass. It was found that in passerines is higher than innon-passerines at all ambient temperatures by 50% at 25°C, 30% at 0°C, 39% at the lowercritical temperature, and 59% at the upper critical temperature. The dependence of waterloss on body mass at different ambient temperatures ( ) wasfound to vary in the same manner as evaporative heat loss. inPasseriformes is approximately 25-60% higher than in Non-Passeriformes (particularly athigh ), which is consistent with the ratio of their levels. Within the thermoneutral zone, the proportion of heatdissipated by evaporation increases by approximately 2.6-fold in small passerines and byalmost 4.1-fold in large passerines with the transition from the lower to upper criticaltemperature. In non-passerines, the proportion of evaporative heat losses increases byapproximately 2.7 times within the thermoneutral zone in both large and small birds. Thehigh basal metabolic rate in Passeriformes involves benefits like a higher maximummetabolic power and the ability to breed at lower ambient temperatures, but it comes witha cost: a significant expenditure of evaporative water. This cost is important because itis found to increase with body size in Passeriformes due to the forced evaporative heatloss, but it shows virtually no increase with body size in Non-Passeriformes. Thus,despite a high significantly increasing ecological opportunities,this way of expanding the ecological niches is possible for the small size class only.These findings suggest that the high level of basal metabolic rate in Passeriformes incomparison to Non-Passeriformes determines the necessity for the former to utilizeconsiderably larger amounts of water for evaporation to maintain the needed heat balance,especially at higher ambient temperatures and at larger body sizes.