The road barrier effect on flying vertebrates has been consistently underestimated, presumably because of the assumption that flight confers the capacity to overcome this challenge. Recent studies, however, have demonstrated that many forest dwelling birds and microbats may be reluctant to traverse the space above the road. One effective solution to this impediment is the installation of vegetated fauna overpasses which provide contiguous habitat connections across even large roads. These structures have been shown to be extremely effective for smaller forest birds, including species known to be extremely reluctant to cross even small spaces. Little is known about the use of vegetated overpasses by microbats. We assessed the patterns of activity and species richness of microbat assemblages in relation to the Compton Road fauna overpass near Brisbane in Australia throughout 2015. Bat vocalisations were recorded weekly using Echo Meter recorders along eight 100m transects positioned perpendicular to the road from the roadside into the surrounding forest and along the overpass.
A total of nine species and two species groups (species that could not be differentiated) were identified during the study, all of which were recorded on the overpass. Bat activity and richness on the overpass was significantly higher than the adjoining forest, although call activity was not significantly correlated with roadside proximity. Activity patterns based on feeding behaviours suggest that the road effect zone extends far into the forest, impacting forest specialist species especially. The vegetation on the overpass, which was planted to resemble the structure and composition of the surrounding forest, is likely to be the key factor encouraging microbat activity on the overpass. The Compton Road overpass appears to successfully disguise road presence and facilitate microbat movements across a major road. This study is the first to demonstrate that vegetated fauna overpasses can facilitate activity and provide natural habitat continuity for a diverse microbat community.
fauna overpasses, vegetated ecoduct, microbats, road barrier effect.