Introductions of mammalian predators have led to extinctions or declines of many species on islands; hence eradications of these mammals have played a major role in biodiversity conservation. However, eradications are costly and sometimes controversial. It is therefore important to conduct carefully designed sampling programmes that allow benefits to native species to be quantified.
In 1996 an eradication operation against two species of rats (Rattus norvegicus and R. exulans was conducted on Kapiti Island (1965 ha) and its small offshore islands. Trials with non-toxic baits had been carried out to help determine the risks to non-target species, and research was undertaken to collect baseline data for measuring the response of vegetation, invertebrates, reptiles and birds to the removal of rats.