Nest Form, Colour and Nesting Habitat Affect Predation Rates of Australasian Warblers (Gerygone spp.) in Tropical Mangroves

摘要

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.%オーストラリア北部の熱帯地域の海岸に広がるマングローブ林では，巣への捕食圧が高いことが知られている。この地域には，2種のセンニョムシクイ類（ハシプトセンニョムシクイG即ツgO乃e〝∽g〝′m打kとマングローブセンニョムシクイG.levigaster）が同所的に生息している。ハシプトセンニョムシクイは主に，暗く生い茂ったマングローブ林内に潮汐によって生じる小川（tidalcreek）の周辺に営巣し，マングロpブセンニョムシクイはマングローブ林縁の干潟（Salt flat）に点在する薮や孤立木に営巣する。近縁な両種は，ともにドーム型の巣を造るが，巣の大きさや色彩，形態が大きく異なる。