Habitat and nest-site characteristics of waterbirds in Pulau Rambut Nature Reserve, Jakarta Bay, Indonesia

Habitat and nest-site selection of waterbirds in Pulau Rambut was studied to reveal interspecific differences and to identify the important features of this island that allow for its large and diverse population of avifauna.; Pulau Rambut is a small island in Jakarta Bay, chosen as a study site due to its large population of waterbirds. Characteristics of nest-sites were studied as well as time partitioning for breeding seasons. Field observations were conducted in January 1990 through November 1991.; There were 15 species of waterbirds breeding in Pulau Rambut: Egrets (5 species), Day Herons (2 species), Night Heron (1 species), Ibises (2 species), Darter (1 species), Stork (1 species), and Cormorants (3 species). These species formed 5 colonies, and each colony had a distinct habitat structure and group of waterbirds nesting on it.; Most species preferred nesting during the rainy season. However, some temporal stratification was observed, probably due to the availability and variety of foods. The overall population of waterbirds in Pulau Rambut showed a continuous breeding season.; Vertical stratification of nest sites was lacking. Waterbirds tended to chose sites on top of the canopy and further from the tree trunks, suggesting that the ground-based predator, the Monitor Lizard (Varanus salvator) were more threatening than aerial predators, namely Brahminy Kite (Haliastur indus) and White-bellied Sea Eagle (Haliaeetus leucogaster).; Selection of vegetation type was influenced by social interaction and physiognomic features of the environment. Social factors include behavior and daily habit, and congeneric avoidance due to similarity in morphology, physiology, behavior, and ecology. Physiognomic aspects included body size, and location within the heronry (center vs. edge).; Factor analyses revealed that there were 5 components which described waterbird nest-sites: nest placement, tree size, inter-nest distance, nest support, and stability, as a result of differences in body size, choice of general vegetation type, and degree of predation.