Conservation management of eastern Australian farmland birds in relation to landscape gradients

Abstract

Summary 1. Birds inhabiting farmland are of conservation concern around the world. In Australia, conservation management has focused primarily on woodland environments. By contrast, semi-natural open areas have received less attention. We argue that long-term conservation strategies should consider broad gradients of environmental conditions. Otherwise, there is a risk that semi-natural open areas will degrade through ‘benign neglect’, and currently common species using these areas will become uncommon. 2. We examined how birds responded to three environmental gradients in an Australian livestock grazing landscape: tree density, grazing intensity and nutrient enrichment. First, we investigated changes in species composition across the environmental gradients in multivariate space. Secondly, we modelled species richness and the response of selected individual species in relation to the gradients. Thirdly, we examined if there were patterns in guild composition and body mass distribution. 3. Tree density was the primary driver of virtually all patterns observed. Species richness peaked at moderately high tree densities. With increasing tree density, species composition changed, foraging guild composition changed and the median body mass of bird species decreased. Small insectivores were more likely to occur in areas with high tree densities, whereas large granivores were more likely to occur in areas with relatively low tree densities. Grazing intensity and nutrient enrichment were less strongly related to bird distribution patterns, although the indirect effects of these gradients may be substantial because they affect tree regeneration. 4. sSynthesis and applications. Relatively dense woodland patches were important for species already of conservation concern, lending support to their active conservation management, for example through livestock exclusion. However, semi-natural open areas also were used by many birds, which represented a different mix of body sizes and foraging guilds. Scattered trees occurring at a range of densities are key habitat elements in semi-natural open areas. However, many scattered trees are dying and are not being replaced by natural regeneration or tree planting. If areas with scattered trees continue to degrade, there is a risk that currently common farmland birds will decline. Management strategies aiming to maintain scattered trees therefore are important, including the planting of individual trees and the adoption of grazing practices that allow for natural tree regeneration.