Bird assemblage changes along a savannarainforest gradient in north-eastern Australia

Abstract

Habitat and landscape gradients can provide insight on how vegetation pattern influence the composition and species turnover in birds. Gradients on mountainsides are particularly suitable as the vegetation can be distinctly stratified. On the western fall of the Australian wet tropics, the vegetation traverses through tropical savanna into tropical rainforest over a relatively short distance. We investigated bird richness and abundance in this transition. Seventeen sites were sampled from lowland (350 m) to upland (1000 m) locations, comprising six zones. Birds were sampled four times between 2006-2007. 125 species of birds representing 38 families were recorded. The pattern of abundance and richness along this gradient was characterised by second-order polynomial relationships. The nadir was where change in vegetation was most rapid; low open woodlands to dry open forest, between 500 and 800 m. We conclude that the avifauna assemblage we recorded along the gradient represents predominantly a woodland bird community that drifts upslope, an upland rainforest community that extends into adjacent tall forests, and an intermediate zone comprising a subset of the two communities. Very few species were ubiquitous. We conclude these intermediate zones may be important linking areas and habitat as climate change continues.