Landscape-scale structuring of arid bird assemblages: Vegetation type influences species composition

Dynamism is a distinctive feature of desert bird assemblages and includes temporary irruptions and wide-ranging flocking behaviour in response to unpredictable food availability. As a consequence, ecologists have hypothesized that temporal and spatial variation in occurrence of desert birds is of sufficient strength to obscure predictable patterns of community structure. Here we examine this hypothesis by assessing species richness and assemblage structure of arid birds in relation to landscape-scale environmental variation in the Finke bioregion, Australia. We surveyed birds at 194 sites stratified according to environmental gradients in vegetation, landform, soil and geology. A total of 107 species were recorded with mean richness of 11.31 species (range 1-33) and mean abundance of 12.47 individuals (range 0-102). Five distinct bird assemblages were discernible by cluster analysis. Analyses to date using constrained ordination techniques (canonical correspondence analysis) demonstrate a strong association between three of these bird assemblages and environmental variation characterised by specific vegetation types, namely chenopod herbland/open shrubland, mulga (Acacia aneura) tall open shrubland, and eucalypt woodland/open woodland. The diagnostic species of each of these clusters as determined by SIMPER-analysis also show a strong association with the respective vegetation types. Our results demonstrate that at a landscape-scale the composition of bird assemblages in the study region is determined by environmental variables particularly vegetation type. Our findings support and broaden the conclusion of Cody (1994) of predictable bird community structure in mulga shrublands of arid and semi-arid Australia.