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

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 fl ats 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 fl ats. 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.

Compositional patterns in terrestrial fauna and wetland flora and fauna across the Pilbara biogeographic region of Western Australia and the representativeness of its conservation reserve system

“…This result is generally consistent with taxon-specifi c analyses of individual species relationships and multivariate analyses of the Pilbara Biodiversity Survey data (Gibson and McKenzie 2009;Burbidge et al 2010;Guthrie et al 2010;Heterick et al 2010;Pinder et al 2010;Volschenk et al 2010;Doughty et al 2011). Among the taxonomic groups examined in these analyses, beetle, scorpion, bird, reptile and ground-mammal patterns all showed strong relationships with soil attributes.…”

“…The sites were positioned across the geographical extent of the region in a stratified array to sample the main climatic gradients, geological formations, landforms, river catchments, soils and vegetation types. The survey fi ndings, published as a series of papers in a dedicated Supplement of the Records of the Western Australian Museum, describe the relationship between the region's physical environment and components of its biota (Gibson andMcKenzie 2009, McKenzie et al 2009;Burbidge et al 2010;Guthrie et al 2010;Heterick et al 2010;Pinder et al 2010;Volschenk et al 2010;Doughty et al 2011). Each of these taxonspecifi c papers related biodiversity survey data to environmental attributes at the site level.…”

Herpetological assemblages of the Pilbara biogeographic region, Western Australia: ecological associations, biogeographic patterns and conservation

“…The study did not identify any reptile assemblage showing a strong affinity to regional riparian vegetation or sites, unlike birds (Burbidge et al 2010) and microbats (McKenzie and Bullen 2010). This is perhaps not surprising, given that in the Pilbara there are few major drainage lines, they do not have extensive well-developed habitats that are distinct from surrounding areas, and any such habitats are scattered.…”

Spatial distribution patterns of scorpions (Scorpiones) in the arid Pilbara region of Western Australia

“…Similarly, we took the Bray-Curtis matrix (based on scorpion occurrences at the same sites) and converted this to a linear vector. Plotting one vector against the other provides a scatter plot in which the slope of the line of best fi t is a measure of spatial correlation, with a slope of zero indicating a complete absence of correlation (see Burbidge et al 2010). In this case, the line was represented by the equation Y = 0.6848 + 0.0001X, indicating a small but detectable degree of correlation.…”

“…The site matrix was derived using the Bray-Curtis measure with a 'dummy' variable added, because of the high incidence of zero values in the matrix . We used normalised values of a subset of 25 of the available environmental variables, chosen according to their inter-correlation values (Burbidge et al 2010) and created a Euclidean distance matrix for comparison with the site matrix. The analysis was limited to the fi ve 'best' variables, and the global match test utilised 99 permutations.…”