The overpass at Lersbakken outside Trondheim, Norway. Photo credit: Trondheim Kommune.
The construction of large infrastructures, such as highways, is known to fragment habitats and restrict wildlife movement, posing significant barriers to species migration and survival. Wildlife crossing structures, such as overpasses, are increasingly implemented as mitigation measures to reduce negative impacts from these developments by enhancing landscape connectivity and reducing wildlife-vehicle collisions.
“By advancing our understanding of wildlife responses to mitigation measures, such as overpasses, we will contribute to more effective conservation planning in the face of infrastructure development”, says Lars Rød-Eriksen, researcher at the Norwegian Institute for Nature Research (NINA).
Monitoring Wildlife Use
As part of the expansion of the European route E6 to a four-lane highway outside Trondheim, Norway, a wildlife overpass was constructed along the new route. To assess wildlife movement between habitats on either side of the highway, experts from NINA conducted systematic monitoring using wildlife cameras from late autumn 2020 to May 2023.
Contribution to Habitat Connectivity
During the monitoring period, researchers recorded more than 3,500 wildlife crossings. The majority of observations (84%) were of roe deer (Capreolus capreolus) and red fox (Vulpes vulpes), while larger cervids, such as moose (Alces alces) and red deer (Cervus elaphus), accounted for approximately 8% of the recorded crossings. This result corresponded well with the species composition in the surrounding areas.
A roe deer crosses the overpass. Photo credit: NINA.
The study confirms that the wildlife overpass indeed serves its intended purpose by facilitating wildlife movement across the highway and contributing to habitat connectivity. However, the long-term impact of the overpass on local cervid populations remains uncertain.
“Continued vegetation growth on the overpass may enhance its attractiveness by providing both food resources and shelter, potentially increasing its future usage, says Lars Rød-Eriksen, researcher at NINA.
Recommendations for Future Research
To fully assess the long-term ecological value of the overpass, the experts at NINA recommends resuming monitoring efforts in the coming years, including studies evaluating wildlife usage of the overpass in relation to changes in local population densities and landscape development on both sides of the highway.
Read the report here (summary in English): The use of a wildlife overpass over European route E6 in Lersbakken in Trondheim by cervids and small mammals 2020-2023.
Contact: Lars Rød-Eriksen