Vegetated fauna overpass enhances habitat connectivity for forest dwelling herpetofauna

The ecological impact of roads and traffic is now widely acknowledged, with a variety of mitigation strategies such as purpose designed fauna underpasses and overpasses commonly installed to facilitate animal movement. Despite often being designed for larger mammals, crossing structures appear to enable safe crossings for a range of smaller, ground dwelling species that exhibit high vulnerability to roads. Less attention has been paid to the extent to which fauna overpasses function as habitat in their own right, an issue particularly relevant to reptiles and amphibians. The Compton Road fauna array (Brisbane, Australia) includes a vegetated fauna overpass which connects two urban forest reserves and traverses a major four lane arterial road. The aim of this study was to quantify the extent to which colonisation of the Compton Road fauna overpass by reptile and amphibian species living in adjacent forests occurred. Pitfall sampling at seven sampling sites occurred between June 2005 and February 2010, starting approximately six months after overpass construction, with additional observational detections throughout this period. The overpass yielded higher species diversity and capture rates compared with the forest areas. Species accumulation curves demonstrated a strong and consistent colonisation rate of the overpass throughout the six year monitoring period, while persistent occupation by species on the overpass throughout the six years suggests permanent colonisation of the vegetated structure as an extension of the natural forest habitat. These outcomes demonstrate that the fauna overpass at Compton Road provides suitable habitat for diverse local herpetofauna communities and suggest enhanced habitat connectivity across the road.