Climate change and the koala Phascolarctos cinereus : water and energy

We studied two groups of koalas during a drought in central Queensland to investigate potential impacts of climatic variability on the physiology and behaviour of this species. The tree use, water turnover, field metabolic rate and diet of koalas during autumn and spring were compared to a similar study of koalas in summer and winter, also in central Queensland, to generate a seasonal picture of the response of koalas to climatic variation. We also compared the microclimate temperature of a range of food and non-food tree species against daily ambient temperatures, to examine the benefit to koalas of using of non-food species. Field metabolic rate, adjusted for body mass, was significantly higher in spring than autumn and there was no difference between males and females. Neither females with pouch young nor those with back young had significantly different FMR to that of females without young, confirming that koalas may compartmentalize energy demands during lactation. Estimations of theoretical water influx, determined from FMR of koalas, were generally lower than water flux determined by tritiated water turnover. This mismatch could indicate that koalas are able to modify their assimilation of energy from browse in order to maximize water intake. Temperature was generally lower in non-food trees used by koalas in daytime than in the food trees, which were generally used at night. Leaf moisture may influence tree selection during periods of extremely high or low temperature, but the physical attributes of trees, such as their capacity to “buffer” koalas against extremes of ambient temperature, appear to be important to selection by koalas. We conclude that koalas adapt their behaviour, using shady trees during the day, but might also employ physiological adaptations, to access sufficient water for evaporative cooling during periods of hot, dry weather.