The relationship between woodland remnant size and bird diversity in an urban landscape in southern Tasmania

There has been much research which relates reduction of habitat to reduction in biodiversity anq often birds are chosen as the best indicators of these changes. In Australia studies in this area have largely focused on the effects on birds in changing rural or forested, rather than urban, landscapes. There has been little research in this area in Tasmania, yet this State has perhaps the highest proportion of original natural habitat remaining of any State in Australia. This study compared the avifauna of adjacent urban and dry sclerophyll woodland sites in the urban fringe of Hobart and found significant differences in bird species diversity between these habitats. For the purposes of this study, the woodland remnants, therefore, could be considered islands and were tested for a species-area relationship according to the principles of island biogeography. The varying size of woodland remnant, from 1 to.3100hectares,simulating'habitat loss' was used to study its effects on the species richness and population density of the woodland avifauna. Data were gathered by the line transect method in these woodland remnants and the results analysed by the DISTANCE software package which gives estimates of population size and density. The results were plotted as a chart of approximate population sizes of the more common 22 species of woodland bird. Depending on what is considered to be the minimum viable population size the chart could be used as an indication of the threshold remnant area of woodland required for these species. In so doing it provides a mechanism by which predictions may be made regarding reductions in populations and loss of entire species as remnants are reduced further by urban expansion. If acceptable levels of remaining biodiversity for dry sclerophyll woodland can be set, then the sort of methodology adopted in this study could be used by natural area managers to predict whether development proposals are likely to re_duce an area of habitat below an ecologically sustainable level.