Tree use by koalas (Phascolarctos Cinereus) on St Bees Island, Queensland : report of a pilot study

This paper reports on a pilot study of tree use by koalas on a tropical Queensland island. Some koalas on St Bees Island use different tree species and different tree forms by night and by day. Ten female and six male koalas were radio-located for 10 days. Six females and three males were radio-located for nine nights. Known fodder species were used most frequently at night but non-fodder species were used most frequently during the day. Many of these non-fodder tree species appeared to have relatively dense canopies giving greater canopy shade which could provide benefits to koalas using these trees in particular weather conditions. Consequently, the behaviour of three female koalas was observed during the day for three consecutive days. When using trees with relatively dense canopies, the koalas moved less and did not breathe so heavily as when using relatively open canopy trees during the day. Although our data are limited, we hypothesise that (1) koalas select trees at nigh tunder a “drive” to feed but select trees used by day under a “drive” to seek shelter; and (2)koalas using closed canopy trees during the day will have a physiological advantage over those koalas that selected trees with canopies that provide relatively little shade. These results have informed the design of an intensive study of koala ecophysiology on St Bees Island. If the findings are substantiated then complex habitat structures may provide better habitat than habitat of simple structure — especially in hot humid environments.