Land use, habitat change and the conservation of birds in fragmented rural environments: a landscape perspective from the Northern Plains, Victoria, Australia

Abstract

Studies of the effects of habitat fragmentation on birds have mainly been carried out at the patch scale, by censusing birds in patches of different size, shape or composition. Here, we use data collected by observers for the Atlas of Australian Birds from 10' latitude/longitude grid cells (landscapes), each 277 km2 in size, to examine the effects of land use and habitat change at the landscape scale in the Northern Plains region of Victoria, Australia. Land birds were tallied for 63 such landscapes and species were classed as "woodland" or "other" species. Attributes measured for each landscape represented natural environmental variation, tree cover and the intensity of human settlement. The Northern Plains has experienced profound environmental change over the last century of agricultural settlement and tree cover now occupies only 6.2% of the region, mostly as large riverine forests. Eighty per cent of landscapes have less than 10% tree cover. Woodland birds showed substantial variation in richness between landscapes and, after accounting for sampling effort, species richness was best predicted by total tree cover and measures of environmental variation (e.g., number of streams). "Other" birds were more evenly distributed between landscapes. Species richness was best predicted by the environmental gradient in rainfall and temperature, although this accounted for only a small amount of variance after correcting for sampling effort. The predictive model for woodland birds indicates that this group is sensitive to habitat change, and implies a substantial loss of species in landscapes that have been almost entirely cleared of woodland habitat. The logarithmic nature of the relationship means that the rate of change in species richness is greatest during the final stages of habitat depletion. With median tree cover of 3.7% for landscapes in the region, this relationship supports the contention that a major decline in woodland birds is underway and that species are being lost from whole landscapes across the region. Attributes associated with landscapes of high conservation value for birds include: extensive overall tree cover, large blocks of woodland habitat, and stream systems with associated habitat connectivity. In this region, these attributes are more likely to occur in areas with broad-acre agriculture rather than intensive irrigation. The analysis suggests that at least 10% tree cover is a minimum goal for an infrastructure of natural vegetation in rural landscapes to prevent serious decline and loss in the woodland avifauna.