Effects of foliage invertebrate availability and forest structure on the abundance of the critically endangered Rota White-eye Zosterops rotensis in Rota, Mariana Islands

The Rota White-eye, Zosterops rotensis, is a critically endangered species endemic to the island of Rota, in the Mariana Islands, western Micronesia. There has been a dramatic decline in both its population size and range over the past few decades. The population, estimated at approximately 1,000 individuals in 1999, is found exclusively in 300 ha of mature limestone forest, though nearby areas of mature limestone forest remain unoccupied. We compared the bird community, vegetation characteristics and foliage-invertebrate density in forest plot pairs with known high and low densities of Rota White-eyes. Discriminant function analysis suggested that certain vegetation characteristics were best at predicting whether a plot was high-density or low-density. High-density plots had more stems with 20-50 cm DBH, more foliage intercepts at 3-9 m, more epiphytes, greater total canopy cover and fewer overall plant species. This information is essential for the protection of the current habitat of the Rota White-eye and for future efforts in the protection and management of this species.