Abstract

Roads are a barrier to mammal movement, yet wildlife passages are infrequently implemented. Alternatively, some species are reported crossing through more common road infrastructure such as bridges and water culverts. I aimed to better understand how mammals use these structures to connect their habitats by investigating potential predictors of their use. My research focused on the Laurentides region in Quebec, where two parallel major roads bisect every ecological corridor linking two national parks. From June 2022 to December 2023, I installed trail cameras to monitor mammals at two bridges and eight large box culverts and placed track boxes in the surrounding habitat for 20 concurrent weeks. Mammals associated with urban landscapes were the most prevalent among the 20 different species or groups of species identified across all sites, of which only 11 made at least one full crossing. Many species from the region were notably absent, particularly large mammals. Six species were often observed in water and were the only species who crossed through sites that had no continuous dry ledge. Minimum water depth to cross a site was the strongest predictor to deter mammals, as the sites with the highest water depths were rarely or never crossed even by water-tolerant species. Much greater bridge use shows that unmitigated culverts are largely unsuitable for mammal movement. I strongly recommend adding dry ledges or shelves to the structures to mitigate the roads’ impacts on connectivity, and wildlife fencing to prevent road mortality and guide animals to sites with these features.