The role of adjacent habitats in rodent damage levels in Australian macadamia orchard systems

Estimates of damage caused by Rattus rattus to macadamia nut crops were determined from several Australian macadamia orchards during the 1995/1996 growing season. Both the extent and pattern of crop damage were associated with the type of adjacent non-crop habitat. Orchards adjacent to large, temporally stable, structurally complex habitats experienced high levels of rodent damage (mean 9.9%). Front row trees adjacent to these stable habitats showed significantly higher damage than trees further into the orchard, suggesting an interaction between the crop and non-crop habitats. Orchards adjacent to highly modified grasslands and other orchard blocks exhibited the lowest levels of damage (mean 0.8%), with the damage in these areas being uniformly distributed. Rattus rattus was the main rodent species responsible for damage. Animals were not distributed uniformly throughout the orchard system. High densities of rodents were found in temporally stable adjacent habitats, while low densities were present in temporally unstable adjacent habitats and cropped areas. The stability and complexity of adjacent non-crop habitats directly affected the potential for rodent damage to macadamia crops. Manipulation of large, temporally stable adjacent habitats therefore could be an effective method for reducing rodent damage in macadamia orchards.