Overbrowsing, and Decline of a Population of the Koala, Phascolarctos cinereus, in Victoria I. Food Preference and Food Tree Defoliation

Roger W. Martin

Department of Zoology, Monash University, Clayton, Vic. 3168.

Tree usage by koalas as a measure of foliage preference was analysed over two years in an open forest containing three Eucalyptus spp. At the commencement of the study, there was significant defoliation of one of the species, Eucalyptus ovata. The koalas showed a significant preference for E. ovata, which became increasingly defoliated as the study progressed. The preference for E. ovata decreased in the second year of the study, probably as a result of a decline in available foliage. It also changed seasonally, with koalas showing stronger preference for E. ovata in autumn and winter than in spring and summer. The preference for E. radiata and E. obliqua was higher in summer, when both species were producing abundant new growth. It is suggested that the koalas are possibly selecting foliage so as to maximize their intake of crude protein.