Talk You shall pass A mechanistic evaluation of mitigation efforts in road ecology

The transportation infrastructure is rapidly expanding and are being upgraded to move goods and people in and out of populated areas. The impacts of roads and traffic are globally recognized as threats to the functioning of healthy ecosystems, and mitigation strategies are increasingly being adopted around the world. However, not all impacts can be fully mitigated, and not all mitigation measures are equally effective. Wildlife crossing structures encompass a broad range of natural (e.g. tunnel roofs) or artificial (e.g. grey and green bridges, culverts, underpasses) structures designed to provide habitat connectivity and reducing animal-vehicle collisions (AVCs). There is much to learn about their effectiveness and how they contribute to the preservation of green infrastructure, e.g. how many and what kind of structures do we need to reach the goals of mitigation. We attempted to contribute to this knowledge gap by studying the movements of 55 GPS-marked moose (Alces alces) in a study area surrounding Oslo Airport Gardermoen, in Norway. Within the study area the bigger roads are to a large degree fenced to avoid AVCs, and there is a large number of different crossing structures. Some of these were specifically built as wildlife passages while others were not. Our approach was to use Step Selection Functions (SSFs) to quantify to what degree different landscape features could be traversed by a moose (step). This model examined the effects of different land cover categories, landscape features, and different road related features such as wildlife fences, crossing structures and traffic volume. Crossing structures where split in three categories based on their expected suitability for wildlife use; 1) wildlife passages, 2) multi-use passages, and 3) grey passage (road bridge or underpass crossing another (fenced) road). Based on parameters from this model we discuss the effectiveness of different crossing structures for moose and how these results can inform us about how frequent such structures should be built to counteract the barrier effect of wildlife fences. We also discuss the effect of disturbance from road including traffic volume on moose movement as well as the effect of other landscape features.

wildlife; crossing structures; fauna passages; wildlife fences; green infrastructure; step selection functions (SSFs); barrier effect; traffic volume