Proceedings of the Vertebrate Pest Conference

Three rat species, the Norway rat, black rat or ship rat, Pacific or Polynesian rat, and the house mouse are among the most widespread and destructive invasive mammals affecting islands. Through mostly unintentional introductions by humans, these rodents occupy >80% of the major islands worldwide. As a consequence of their omnivorous diet and large incisor teeth, introduced rats are probably the invasive animals responsible for the greatest number of plant and animal extinctions on islands. The effects of house mice on island ecosystems are less well known when compared with rats. We have reviewed past diet studies of these 4 omnivorous rodent species. Our review suggests that due to the high variability in diet, as well as direct and indirect effects of predation, all 4 species pose potential threats to many plants and animals on Pacific islands. Although rodent diets greatly differ among sites, diets appear to roughly follow this pattern: Norway rats and house mice generally consume proportionally more animal than plant (Norway rats consume many vertebrates and house mice mostly consumes arthropods), whereas black and Pacific rats generally consume proportionally more plant than animal. Studies specifically linking rodent diets with the population status of surrounding biota are needed in order to clarify the effective impacts of these rodent species. Much could be learned from rodent removal experiments, which could further expand our knowledge of invasive rodent species effects, and native species conservation, on islands.