Co-use of existing crossing structures along roads by wildlife and humans: Wishful thinking?

Background/Question/Methods

Existing crossing structures built for human purposes such as train underpasses, road underpasses, and water culverts are a potential alternative to purpose-built wildlife passages. Our objective was to understand: How much are these structures being used by mammals and how are human activity and wildlife use related? We analysed which species use the crossing structures and their crossing success ratios. We also assessed the human and wildlife use during the course of the day and how their daily frequencies are related. We placed motion-detection infrared camera traps along Highway 10 East which bisects the Northern Green Mountain linkage ecoregion. In total, eight existing crossing structures of the three types mentioned above were studied using four cameras at each site for time periods of up to 778 days. The Shannon Diversity Index was calculated for each of the sites for all mammals detected and for all mammals confirmed to have successfully crossed through the structure. Wildlife detections and human activities were associated by day and Kendall’s Tau tests were performed for the 5 species with the most detections. Finally, species with at least 10 detections were classified into five categories based on observed human co-use levels.

Results/Conclusions

From the 1.3 million photos taken, we observed 3459 mammal detections from 23 mammal species. Confirmed outcomes showed a 58.8% crossing success ratio. The species observed the most often were raccoon, white-tailed deer, and red fox. These had the highest crossing success ratios and were the only species observed at all eight study sites. The singular road underpass had the lowest overall diversity index of all the sites and the most raccoon detections. The five water culverts had diversity indexes comparable to those of the two train underpasses yet are unsuitable for white-tailed deer due to water presence. Human activity was the highest during daytime hours, opposite to mammal detections which peaked during crepuscular hours. Kendall’s Tau tests showed strong correlations, both positive and negative, between full crossings and daily human activity rates for four out of five species evaluated. Some species known to be in the area were never detected and others never successfully crossed on days with any human activity. These results suggest that only certain species are tolerant of human activities. Measures such as retrofitting existing crossing structures and building wildlife passages and fences should be considered for species less tolerant of human co-use.