Communally Nesting Migratory Birds Create Ecological Hot-Spots in Tropical Australia

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.

Impacts of Bush Encroachment on Wildlife Species Diversity, Composition, and Habitat Preference in Ol Pejeta Conservancy, Laikipia, Kenya

“…This implies that spatial and temporal habitat heterogeneity drives faunal species diversity and composition from local to regional to global scales. Hence, aggregation of resources may create dynamic impacts where these small sites/patches become a focus for higher proportion of faunal diversity and composition [20]. According to Sirami et al [21] savannah ecosystems are diverse in structure and floral composition; hence different guilds will use different habitats based on their requirements.…”

How do predators and scavengers locate resource hotspots within a tropical forest?

“…The climate of the area is highly seasonal, with a mean annual rainfall of 1744 mm largely falling during the summer monsoon (December to April) while the rest of year remains hot and dry with frequent fires (Bureau of Meteorology 2016). The birds attract a diverse assemblage of local predators and primary consumers that feed on fallen nestlings (waterlogged branches often fall to the ground, thus providing access to live or freshly-dead nestlings), and invertebrates in the guano-enriched soil beneath the tree (Natusch et al 2016). The birds attract a diverse assemblage of local predators and primary consumers that feed on fallen nestlings (waterlogged branches often fall to the ground, thus providing access to live or freshly-dead nestlings), and invertebrates in the guano-enriched soil beneath the tree (Natusch et al 2016).…”

“…Based on detailed camera trapping data from beneath starling colonies (Natusch et al 2016), we were confident that animals would visit the audio stimuli throughout the day, so justified beginning our experiments in the late morning (11.00 hours, as above). 10 m away on a nearby tree, and facing the redeployed audio stimuli.…”

“…For example, knowledge of attractant cues can facilitate control of problem fauna by identifying effective cues for trapping (Crossland et al 2012), and minimizing cues that attract those taxa to areas where they are especially problematic (Rodda et al 1999). These cumulative nutrients attract a dense and diverse assemblage of primary consumers and predators that gather to exploit this resource (Natusch et al 2016). In the case of a large resource 'hotspot' used by many different species, the proximate cues used to locate the resource may well differ among taxa.…”

“…Based on our knowledge of this system and the animals frequenting it (Natusch et al 2016), we predicted that visual cues would be unimportant for all taxa because the dense rainforest precludes the use of sight in locating starling colonies until the predator is within several metres of the colony. We conducted field experiments to control the kinds of information available to the forager, and to directly examine species differences in the proximate cues used to locate resources.…”