No abstract

Water turnover for koalas is positively correlated with the moisture content of selected trees suggesting that browse choice was driven by water requirements in summer but energy demands in winter. We compared the distribution of the koala to relative humidity and found that the bioregional delineation of the koala?s range corresponds closely to regions experiencing an average 9am relative humidity of less than 80% in February. This indicates that the northern coastal distribution of the koala may be limited by respiratory evaporative water loss as a cooling mechanism.

At St Bees Island, central Queensland, during drought conditions from July 2001 to April 2003, 85% of koala deaths occurred when browse moisture fell below 51% fresh weight. Drought-induced mortality (and changing frequencies or intensities of drought due to climate change) may have a considerable effect upon this population.

Several studies report methods for determining the age of juvenile Queensland koalas (Phascolarctos cinereus adustus) but these are mostly based on data from captive populations, because observing the birth of koalas in their natural habitat is extremely rare. We identified the exact date of birth for two male joeys by initially observing one within minutes and the other within hours of their birth, at St Bees Island, central Queensland. Successive measurements of head length, as these individuals matured, were used to construct a growth curve for free-ranging juveniles. When tested, only one previously published growth curve (based on body mass) was able to accurately estimate the age of the two joeys. Both methods were then tested for precision using morphometric data for other juvenile koalas in the St Bees population. The estimation of age of juvenile koalas was considerably more precise when based on head length. These results demonstrate the inaccuracy that may be inherent in growth curves derived from captive animals and also show that estimates of age based on data from individuals in a particular population or locality may not be accurate throughout the range of a species.