Where do wildlife cross the road? Experimental evaluation reveals fauna preferences for multiple types of crossing structures

Abstract

Crossing structures are frequently installed worldwide to ameliorate the impacts of road and rail infrastructure on wildlife populations, yet their effectiveness is often uncertain. We monitored various species at multiple drainage culverts, dedicated wildlife underpasses, and a large viaduct, as well as in adjacent bushland over 12 months along a 13 km section of a new highway in eastern Australia. We quantified the frequency that species approached each structure relative to their presence in adjacent bushland, and compared species’ utilisation preferences between the three types of crossing structure. Of the 46 species detected, only 28 were detected at crossing structures. Brush turkeys (Alectura lathami), echidnas (Tachyglossus aculeatus), European brown hares (Lepus europaeus), rats (Rattus spp.), red-necked wallabies (Macropus rufogriseus) and swamp wallabies (Wallabia bicolor) were less frequently observed at crossing structures than in adjacent bushland. Feral cats (Felis catus) and European red foxes (Vulpes vulpes) were observed 3.5 and 2.7 times more frequently at crossing structures than in adjacent bushland. Culverts, underpasses and the viaduct performed equally for all species except for swamp wallabies and hares, which preferred the viaduct. Feral cats, foxes, dingoes (Canis familiaris), and hares were responsible for 76% of the successful crossings, and individually identified feral cats and foxes repeatedly crossed the road during the study period. We recommend increased use of experimental study designs to evaluate the effectiveness of crossing structures and provide construction authorities with reliable information on structure performance.

Keywords

• Connectivity
• Fauna underpass
• Road ecology
• Toowoomba Bypass
• Urban ecology
• Wildlife impact mitigation