Nest form, colour and nesting habitat affect predation rates of australasian warblers (Gerygone spp.) in tropical mangroves

Nest predation is high in mangals (mangrove communities) of the Australian monsoon tropics. The Large-billed Gerygone Gerygone magnirostris and Mangrove Gerygone G. levigaster are warbler-like birds that build domed nests, which are very different from each other in size, form and colour. Large-billed Gerygone forages and builds nests along tidal creeks where vegetation is tall and dense, whereas Mangrove Gerygone primarily nests in shrubs around the edges of bare salt flats and forages in both habitats. Using artificial nests that mimicked those of the two species, we tested whether differences in nest appearance, including form and colour, were adaptations to avoid nest predation. Artificial Mangrove Gerygone nests in their main nesting habitat were predated less frequently than those on tidal creeks, whereas predation rates on artificial Large-billed Gerygone nests did not differ between habitats. Our results suggest that Mangrove Gerygone nests are built in the primary breeding habitat to avoid nest predators. In addition, we identified a nest predator, the Yellow Oriole Oriolus flavocinctus. � Yamashina Institute for Ornithology.