Nectar Intake and Water Balance for Two Species of Australian Honeyeater, Lichmera indistincta and Acanthorhynchus superciliosis

Abstract

Two species of Australian honeyeater, Acanthorhynchus superciliosis and Lichmera indistincta, have body masses that decrease uniformly for most of the night but increase at varying rates throughout the day. The greatest rates of increase occur during the first hour of foraging and seem to be caused primarily by enhanced nectar intake and increased retention of nectar water. Birds appear to repay at least 50% of their overnight water deficits during this period. Subsequently, the remainder of the deficit is repaid at a much slower rate, with the water that is accumulated combining with lipid storage to produce a gradual increase in body mass. The rate of body mass increase for both species of honeyeater frequently rises during the last b h before dusk. It is suggested that this occurs because of a further reduction in cloacal fluid output. Birds maintain similar patterns of body mass and water balance variation when provided with artificial nectar of different concentrations. Although they recover less water from the alimentary canal when switched from a 0.4-M to a 1.2-M sucrose solution, they compensate for this by lowering their rates of pulmocutaneous water loss.