Habitat usage of Rattus rattus in Australian macadamia orchard systems: implications for management

Rattus rattus is the main species responsible for causing damage to Australian macadamia crops and previous studies have shown that these animals utilise both the orchard and adjacent non-crop habitats. Australian macadamia orchards are a three compartment system consisting of the orchard (tree and ground layers) and the adjacent non-crop habitat. The development of an effective management strategy to reduce damage due to rodents requires an understanding of the utilisation of and interactions between the different habitat compartments of the system. The use of tetracycline as a biomarker revealed a strong two-way interaction by rodents between the orchard and the temporally stable adjacent habitats. This interaction was consistent within orchards in Queensland and New South Wales. Nut damage was found to occur within the canopy of the tree indicating that the interaction occurs between the adjacent habitat and the tree layer of the orchard. Capture and biomarker studies suggest that the observed bi-directional movement of rodents between the orchard and the adjacent habitat actually consist of two separate processes: bi-directional foraging into the edge of the orchard by individuals from the large population stratum in the adjacent habitat and uni-directional dispersal and accumulation of individuals from the orchard interior into the adjacent habitat. As the adjacent habitat supports high numbers of rodents and is implicated in both processes, that is, as a source for foragers which results in high edge damage and as a sink for orchard dispersers, it is central to the damage process and should be the focus for control programs.