Spatial ecology of woodland birds in agricultural-woodland mosaics: patterns and processes at multiple spatial scales

The current decline in global biodiversity has largely been blamed on agricultural land-use. Within agricultural landscapes, which cover more than 40% of the globe’s terrestrial surface, species loss has been attributed to the loss, fragmentation and degradation of habitats such as grasslands, woodlands and forests. Within eastern Australia, the original extent of temperate woodlands largely coincides with the South-eastern Temperate Grazing Region, known as the sheep-wheat belt. This region contributes a significant proportion of Australia agricultural productivity and has been extensively cleared with less than 20% of temperate woodlands remaining in isolated fragments and riparian corridors. As a consequence of changes to habitat and landscape structure woodland birds have been adversely affected, with species previously thought to be common and widespread undergoing recent declines in the agricultural regions of south-eastern Australia. Previous research investigating the decline of forest or woodland birds in agricultural landscapes, have largely considered assemblages at the patch or site scale and studies have been strongly focused on the effects of habitat fragmentation. Further research is required that encapsulates the entire agricultural-woodland mosaic including the properties of landscape structure at multiple spatial-scales. Therefore I utilised a multi-scaled approach to conceptualise landscape structure at three, hierarchically organised, spatial scales: site-level, patch-level and landscape-level. This approach is useful for identifying the relevant spatial scales of ecological processes and allows interactions to operate across multiple spatial scales. I aimed to quantify the influence and relative importance of interactions between ecological processes such as interspecific competition and nest predation and landscape structure at multiple spatial scales for the distribution, abundance and composition of species within woodland bird assemblages. The objective of the study was to test the generality of several suggested ecological theories, each with significant implications for the conservation of woodland birds in agricultural landscapes. Using empirical data from a case study in southern Queensland, I found that even in extensively cleared agricultural landscapes with less that 30% woodland habitat remaining, the effect of habitat fragmentation per se was negligible compared to the influence of habitat structure and interspecific competition from the noisy miner (Manorina melanocephala) and the yellow-throated miner (M. flavigula). Within the study area Manorina honeyeaters had the most important effect on woodland bird species and assemblages. These aggressively territorial honeyeaters influence woodland-dependent birds at multiple spatial scales ranging from individual nests and woodland sites to the entire woodland mosaic. The noisy miner is particularly aggressive and appears to have benefited from agricultural land-use. The occurrence of this species increases in response to decreasing habitat complexity and increasing land-use intensity at multiple spatial scales. A major finding of this study suggests that the noisy miner is more abundant in less productive landscapes. This is in contrast with previous research that suggests the noisy miner prefers highly productive landscapes. In addition, landscape productivity interacts with a preference for low shrub cover, where noisy miners rarely occupy highly productive landscapes with high shrub cover. These findings suggest that habitat rehabilitation would be most beneficial in the most productive landscapes. These results have important implications for the conservation management of woodland birds in eastern Australian agricultural landscapes. The results highlight the importance of managing threatening processes such as increasing interspecific competition and nest predation at multiple spatial scales. The results also highlight the influence of surrounding land uses on woodland bird populations with significant implications for declining populations of woodland birds isolated within agricultural landscapes. The results show how even woodland-dependent birds confined to woodland habitat are influenced by landscape-scale ecological processes and respond to the entire landscape mosaic, including variability in the production matrix.