In much of the arid rangelands of Australia the common large mammalian herbivores are the native marsupials, the Red kangaroo (Megalein rufa) and the Euro (Mucropus robustus), and the introduced eutherian species, the domestic sheep (Ovis aries) and the feral goat (Capra hircus). In the north west of New South Wales a study was carried out to examine the patterns of water usage during summer of these species when they were free ranging in the same area. Drinking frequencies, water turnovers, electrolyte concentrations and diet preferences were determined and information obtained on movements and dispersal from watering points.
The marsupials had a much lower water usage than either of the eutherians. The tritiated water turnover of the goats was three times and that of the sheep four times the value obtained for kangaroos. While much of the difference between the marsupials and eutherians appeared to be due to fundamental physiological differences the high water usage of sheep was in part related to the high intake of halophytic plants in their diet.
The water turnovers of the Red kangaroos and Euros were not found to be different. Drinking studies and urine osmolalities suggested, however, that the open plains dwelling Red kangaroos had a higher water requirement than the hill inhabiting Euro.
The principal components of the diets of the Red kangaroo were grasses; of the Euro, grasses and shrubs; of goats, trees and shrubs; of sheep, halophytic shrubs.