Targeted field testing of wildlife road-crossing structures: koalas and canopy rope-bridges

The suitability of structures installed to enable safe passage of wildlife across a road is most frequently determined by monitoring of structures after new roads are built. Rarely are new structures field tested before installation. We installed canopy rope-bridges in an area frequented by koalas (Phascolarctos cinereus) with the explicit aim of determining whether koalas might use such structures. Rope-bridges were of four different designs to maximise the likelihood that one might be used, as a precursor to further replication. Infrared cameras were installed on the rope-bridges as well as on two nearby reference trees to compare frequency of use. Over a monitoring period of 2.9 years no koalas were detected on the rope-bridges whereas koalas were recorded on the reference trees on 34 and 41 different 24-h periods. Rope-bridges may not be suited to an arboreal mammal that is inclined to travel along the ground to move between trees.