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Predicting cassowary-vehicle collision in the Wet Tropics of Australia

Bruce Webber , Matt Bradford, Noboru Ota, David Westcott

Abstract

Context. Roads act as significant disruptors to wildlife movement through landscapes, even in relatively undisturbed areas. Large terrestrial vertebrates often choose to cross roads, which brings risk of injury or mortality from vehicle collision. In the Wet Tropics Bioregion of Queensland, Australia, the range of the southern cassowary (Casuarius casuarius) spans a diversity of habitats and intensity of road network development. There has been a large increase in the human population within cassowary habitat in recent decades and at local scales there remains concern over increasing mortality caused by vehicle collision. Aims. To inform management decisions on where best to direct collision mitigation resources based on identifying environmental factors that correlate with higher collision risk. Methods. We collated 28 years of data on cassowary-vehicle collisions from across the bioregion and sought to identify ecological, physical and anthropogenic correlates of collision at both landscape- and location-specific scales. Key results. We identified a major hotspot of reported cassowary-vehicle collisions in a large area of coastal lowland between Innisfail and Mission Beach. At a landscape-scale, vehicle collisions increased significantly when the proportion of cassowary core habitat in the landscape was >50% and as the density of major roads increased. To a lesser extent, when minor road density exceeded 400 m/km2. At a location-specific scale, vehicle collisions are more likely to occur on straight sections of major roads that have high canopy cover on both sides of the road and were less likely to occur on roads passing through land use types with low canopy cover. Conclusions. Our findings highlight the significant challenges faced in effectively addressing the cassowary-vehicle collision problem in the Wet Tropics Bioregion. Where cassowary habitat and roads intersect, cassowary mortality will occur. Implications: Construction of new roads within rainforest should be avoided where possible and over- or under-passes should be constructed on new and existing major roads that intersect cassowary habitat and where location specific correlates of cassowary collision exist. In addition, further collision mitigation measures such as traffic slowing should be targeted with these results in mind.

WR23089  Accepted 18 March 2025

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