How do ambient and structural variables influence the entry into and full passage of drainage culverts by mammals and their ability to act as wildlife passages?

Abstract

Roads present a significant barrier to wildlife movement for many species. While designated wildlife crossing structures have been heralded as an attractive solution to many of the problems associated with roads, they are often prohibitively expensive. Autoroute 10 in Southern Quebec is one of many highways in Canada that would benefit from such structures, but currently has none in place. However, the highway has a series of periodically placed drainage culverts designed to allow water to cross underneath the road surface. Through monitoring trail camera footage inside of 13 drainage culverts, and animal track stations along a 20 kilometre stretch of highway A10, this project aims to (1) determine what factors influence the number of full passages of drainage culverts by mammals, and (2) parse the effects that these factors have on the entry into and subsequent full passage of drainage culverts by individual animals. Overall, 20 species were observed outside of the drainage culverts in this study, but only animals highly tolerant to water, including raccoons and American mink, were observed fully crossing the structures with regularity. Water level and polyethylene as a construction material were the strongest deterrents for both the number of full passages, as well as entry into the culverts. Additionally, we found that many factors influenced an individual entering a culvert, while no variables impacted its full passage once it had entered. Moving forward, this data will be invaluable in determining where best to focus future habitat fragmentation mitigation efforts along highway 10. In this study we introduced zero-inflated negative binomial generalized linear mixed models as a statistical method in a road ecology study for analyzing the effects that variables have on excess zeros in the data, as well as the value of combining trail camera data inside of drainage culverts with track data in the adjacent habitat. We conclude that drainage culverts are ultimately not suitable substitutes for designated crossing structures for mammals, and recommend that where it is not feasible to install designated wildlife crossing structures, dry ledges be installed in existing drainage culverts to better allow small- and medium-sized mammals to safely cross under the road surface while avoiding the water inside of them. Future road ecology studies are needed along all major highways, both with and without mitigation measures already in place, to better understand the effects that roads are having on wildlife