Does wildlife crossing infrastructure work? A case study of three canopy-bridge designs and exclusion fencing from Moreton Bay Regional Council, Queensland

Abstract

Although fauna crossing structures have been installed throughout the world, most studies have been of underpasses and overpasses. Canopy-bridges, however, have received much less attention. In addition, although exclusion fencing is used extensively, its effectiveness has rarely been assessed. Since 2015, Moreton Bay Regional Council (MBRC), in southern Queensland, Australia, has installed various mitigation structures at 21 sites. This study compared the use of different designs of canopy-bridge and assessed the effectiveness of exclusion fencing via camera monitoring and roadkill records. A total of 3151 detections of five arboreal species were made on the canopy-bridges at an average of 0.51 crossings per day for both rope cages and rope ladders and 0.64 on rope cages and 0.77 on rope ladders when a poorly used bridge of each type was excluded. A single aluminium ladder had 33 crossings (0.15 crossings per day) but was available for only a short time. Roadkill rates of all species declined by 84% at sites with underpasses and fencing compared to 93% at sites without, but only 39% at control sites. This may be due to the canopy-bridges or the addition of complementary infrastructure, such as signage, pavement stencilling and driver awareness.