Seasonal field energetics and water influx rates of the greater bilby (Macrotis lagotis)

Abstract

Water and energy requirements of free-living male and female greater bilbies (Macrotis lagotis) were measured over two summers and two winters on Astrebla Downs National Park in far south-western Queensland, Australia, by means of the doubly labelled water method. Mean water influx rate of the bilby (mean body mass: summer 928 g; winter 848 g) did not differ between summer (63.1 mL day^–1) and winter (53.1 mL day^–1), but mean field metabolic rate was significantly higher during summer (617.2 kJ day^–1) than in winter (480.3 kJ day^–1). The comparatively low water influx rate of the bilby (significantly lower than that predicted for a 887-g marsupial: P < 0.001) indicated that bilbies have the ability to conserve water in the wild. In contrast, field metabolic rate of the bilby did not differ significantly from that predicted for a marsupial of its body mass (P = 0.999). Bilbies were able to obtain sufficient food and water to satisfy energy and water requirements in three out of the four study periods. However, they were in negative energy and water balance during one study period, suggesting that they are susceptible to nutrient and water stress. The relatively low body fat stores of bilbies in the wild also indicate that they are vulnerable to periods of low food availability. The metabolic strategies of the bilby are only partly suggestive of adaptation to arid conditions.