Battle for the Pacific: It's rats vs lorikeets in a fight for survival in eastern Polynesia
Arguably the most serious threat facing endemic birds of the tropical Pacific is posed by invasive species. Island birds are particularly susceptible because of naturally small populations, confinement to islands that may be subject to rapid environmental changes and an inherent 'ecological naivety' with respect to introduced predators and competitors of continental origin. Black rats Rattus rattus in particular, have decimated island bird populations worldwide - a situation reflected by the plight of the Vini lorikeets of eastern Polynesia. A review of the literature, published and unpublished records and anecdotal information suggests a close parallel between the decline in abundance and distribution of lorikeets and the progressive colonisation by black rats of islands across the region. Surveys of rats and lorikeets on islets of the Tuamotu atolls in French Polynesia revealed a highly significant negative relationship between black rats and the abundance and density of lorikeets - in most cases the two were mutually exclusive. However, in some instances lorikeets and black rats co-existed, though lorikeet densities were lower than on adjacent rat-free islets. These results, and information from other island groups presented here, suggest there may be particular conditions (at least in the short-medium term) under which black rats and lorikeets can co-exist. While further detailed investigations are required to assess these relationships adequately these preliminary results point to potentially significant in situ conservation implications for the group and other similarly susceptible species in the region. For example, it is currently impractical to eradicate rats from most high, rugged Pacific islands. However, if lorikeet populations are able to persist under specific conditions (e.g., low rat density and high nest resource availability), then it would be possible to target important areas for rat control, nest protection and supplementation at key times. These and other conservation and research requirements are discussed.