Seabirds impose a high-nutrient, high-disturbance regime on the islands on which they nest, resulting in higher nutrient cycling rates, plant nutrient uptake and leaf nutrient content. On islands off the coast of New Zealand, seabird-dominated islands support greater densities of soil- and litter-dwelling consumer biota. We predicted that islands with high seabird densities would have higher levels of leaf damage as a result of higher densities of foliar consumers (herbivores and pathogens).
The kiore or Polynesian rat (Rattus exulans) has been suggested as the probable cause for reduced reptile, seabird and invertebrate faunas on many of the northern offshore islands of New Zealand, but the evidence is largely circumstantial and it is based on comparisons between islands with and without kiore. In 1977, kiore colonised a small island in the Mokohinau Group (Hauraki Gulf), where they caused a dramatic drop in lizard numbers. Their impact upon seabirds appeared minimal.