POPULATION TRENDS OF THE FOREST BIRD COMMUNITY ON THE PACIFIC ISLAND OF ROTA, MARIANA ISLANDS

The Pacific island of Rota is part of the Mariana archipelago, and is located approximately 60 km north of the island of Guam. Two Rota endemics, the Mariana Crow (Corvus kubaryi) and the Rota Bridled White-eye (Zosterops rotensis), have declined dramatically in the last 20 years. We examined trends in abundance of eight terrestrial bird species (six native, two exotic) on Rota between 1982 and 2004, and found that seven of them declined significantly, with five species showing declines >50%. Only Micronesian Starlings (Aplonis opaca) increased in abundance. Declines occurred in species abundant in both forested and open habitats, suggesting that the declines were unlikely to be simply the result of deforestation. While the introduction of the brown tree snake (Boiga irregularis) on Guam caused the collapse of that island's avifauna, we do not believe that Rota's declines are due to the establishment of a snake population. Other, as yet unidentified, agents are likely to be responsible. We suggest that future research into the causative agent(s) of decline focus on the comparatively common declining species, rather than studying small populations of endangered species.