Foraging Behavior and Microhabitat Use of Two Species of White-Eyes (Zosteropidae) on Saipan, Micronesia

I studied Golden (Cleptornis marchei) and Bridled (Zosterops conspicillatus) whiteeyes on Saipan in the Mariana Islands, Micronesia.I collected comparative data on social behavior and use of tree zones, foraging surfaces, foraging methods, perch sizes, and tree species in native limestone forest and tangantangan (Leucaena leucoephala) thickets.Unlike the flocking Bridled White-eyes, Golden White-eyes were territorial, but the species were aggressive interspecifically.Bridled and Golden white-eyes were similar in their use of limestone forest and tangantangan thickets as foraging habitats.Compared with Bridled White-eyes, however, Golden White-eyes were more generalized foragers (i.e. less specialized on the top outer forest strata, on live leaves as foraging substrates, and on gleaning as a foraging tactic).Golden White-eyes also preferred to forage among dead leaves, on branches, and on fruit, and they foraged by probing.Similarities by both species in their use of limestone forest and tangantangan thickets indicate that they did not alter their foraging strategies greatly to use the different habitats.This flexibility in habitat choice may explain in part why these species have persisted in the face of periodic typhoon damage and extensive humancaused habitat change.Despite the differences in foraging ecology between the species, interspecific aggression indicated that they competed for resources.In temperate communities, species can be ecologically very similar but rarely compete; in this tropical island community, species with only general ecological similarities may still compete for resources.