Abstract
Large numbers of metallic starlings (Aplonis metallica) migrate annually from New Guinea to the rainforests of tropical Australia, where they nest communally in single emergent trees (up to 1,000 birds). These aggregations create dense and species-rich faunal “hot-spots”, attracting a diverse assemblage of local consumers that utilise this seasonal resource. The starlings nested primarily in poison-dart trees (Antiaris toxicaria) near the rainforest-woodland boundary. Surveys underneath these colonies revealed that bird-derived nutrients massively increased densities of soil invertebrates and mammals (primarily wild pigs) beneath trees, year-round. Flying invertebrates, nocturnal birds, reptiles, and amphibians congregated beneath the trees when starlings were nesting (the wet-season). Diurnal birds (primarily cockatoos and bush turkeys) aggregated beneath the trees during the dry-season to utilise residual nutrients when the starlings were not nesting. The abundance of several taxa was considerably higher (to > 1000-fold) under colony trees than under nearby trees. The system strikingly resembles utilisation of bird nesting colonies by predators in other parts of the world but this spectacular system has never been described, emphasizing the continuing need for detailed natural-history studies in tropical Australia.
Highlights
In most ecosystems, the spatial and temporal distribution of resources drives faunal distributions [1, 2]
Starlings nested in only three tree species: poison-dart trees (Antiaris toxicaria 71%); milky pines (Alstonia scholaris 19%); and Morton Bay ash (Corymbia tesselaris 10%)
Colony trees were always tall, with smooth bark, large trunks and branches separated from the surrounding canopy (Fig 1)
Summary
The spatial and temporal distribution of resources drives faunal distributions [1, 2]. All animals live in spatially and temporally heterogeneous landscapes, varying greatly in productivity, resource abundance and species density Such heterogeneity is often subtle within habitats, but sometimes, concentrations of specific resources create dramatic impacts such that small sites become the focus for a high proportion of all faunal activity [3]. Some faunal concentrations are seasonal, such as Nile crocodiles (Crocodylus niloticus) gathering at points in rivers where wildebeest cross, or grizzly bears (Ursus arctos ssp.) congregating at salmon spawning sites [6, 7]. These resource concentrations can influence vital population parameters such as rates of reproduction and survival [6, 8]. Massive aggregations of wildlife are significant for conservation (e.g. vulnerable to threatening processes), management (e.g., over-exploitation by hunters) and tourism (e.g., support major tourism initiatives; [3, 8, 7, 9])
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