Birds in a vast arid upland: avian biogeographical patterns in the Pilbara region of Western Australia

WA Museum Records and Supplements | Updated 7 years ago

ABSTRACT – We surveyed for the presence/absence of bird species at 297 sites, each of 16 ha, chosen to represent the geographical extent and diversity of terrestrial environments across the Pilbara biogeographic region, Western Australia. We recorded 132 species with an average of 19.1 species per site with a range from 3 to 49. Sampling was carried out over a six-day period in each of two seasons, with visits of 0.5 to 1.0 hour to each site. The diurnal time of sampling at a site was varied in an effort to maximise the detection of species present.

Environments sampled included stony hills, slopes and plains, massive rocks and scree slopes, clay plains, saline muds, deep sands and riverine sites. Vegetation on most sites consisted of hummock grasslands of spinifex (Triodia spp.), usually with widely scattered shrubs or eucalypt trees, while sites on alluvial plains typically supported bunch grasses, saline flats had samphires, run-on areas in the southern Pilbara often supported stands of mulga, and riparian sites had vegetation varying from shrubs to gallery woodlands. Bird species richness was highest in riparian sites and lowest on samphire flats. Patterns in species composition were correlated with vegetation and substrate variables, including soil depth, ruggedness of the topography, soil chemistry and the presence of trees or shrubs. Variation partitioning of results from a PCNM analysis, however, indicated that only 7% of the observed variation in species composition could be attributed solely to the 25 environmental variables we measured, suggesting that much of the Pilbara is relatively uniform from the perspective of terrestrial birds. These results suggest that the existing conservation reserve system is likely to adequately conserve most of the variation in terrestrial bird communities in the Pilbara. However, riparian vegetation, with its distinctive bird assemblages, requires special conservation attention. These areas are of limited extent in the Pilbara and are subject to pressures such as degradation by domestic and feral stock grazing, weed invasion and disturbance by mining infrastructure and groundwater extraction.