Water turnover and the northern range of the koala (Phascolarctos cinereus)

We studied a population of koalas at St Bees Island, central Queensland, where diet selection was limited and browse moisture was higher in winter than summer. Water turnover on St Bees Island was significantly higher in summer (95.6 mL kg-0.71 day-1) than in winter (71.1 mL kg-0.71 day-1) and was also significantly higher than reported for Springsure during summer. These results support the hypothesis that water turnover is obligate in winter. It also appears that koalas select browse of high leaf moisture to facilitate cooling by respiratory evaporative water loss during summer. We postulate that the northern coastal distribution of the koala may be limited by its capacity to achieve cooling by this mechanism in summer under conditions of high relative humidity.