Dispersal by subadults is the principal source of gene flow between groups of koalas in Queensland, so understanding the behaviour of these immature animals is a priority for understanding the ecology of the species. Recent reports postulate that dispersing young koalas may inherit maternal tree selection, but avoid competing with adults. We compared the tree use and diet of adult female koalas with that of their offspring on St Bees Island, Queensland, using radio-tracking and faecal cuticle analysis, to examine this prediction. Koalas at St Bees Island used both fodder and non-fodder species during daytime, moving into fodder species at night. Koala diets were dominated by Eucalyptus tereticornis with E. platyphylla and Corymbia intermedia also represented. Utilisation of daytime tree species was diverse, but at night koalas were found almost exclusively in those species present in their diet. Use of trees during daytime by natal young and young adult koalas were similar to that of maternal adults, but tree use by intermediate stages (independent and dispersing young) during daytime varied from that of the mothers. This resource separation indicates that if tree utilisation for resting is learned from the mother, young animals are excluded from preferred trees while dispersing.