Bigger isn’t always better – especially if you’re a rodent

Voles are pedestrians, too, and need just as much help crossing the road as the big animals, says new research from the University of Alberta.

“There has been a mindset that bigger is better–driven by research on large mammals and especially bears,” said Dr. Colleen Cassady St. Clair, from the Department of Biological Sciences. “This research shows that small affordable culverts, which can be placed with high frequencies while building roads, are very effective conduits for small mammals.”

The study, recently published in the Journal of Applied Ecology, investigated how small mammals–meadow voles, red-backed voles and deer mice–used crossing structures built across the Trans-Canada Highway. Cassady St. Clair and graduate student Wayne McDonald looked at size, vegetative cover at the entrances of the structures and the distance from home ranges to determine what kind of structures the animals would use the most.

The team captured the animals on one side of the crossing structure several different times to ensure that they had residency at that spot. They then moved them to the other side of the structure and released them–giving them a motivation to return “home.” Before the release the researchers coated the animals with fluorescent dye so that, with a black light, they could monitor their return paths.

“We were apprehensive about the possibility that this manipulation would set animals up to be killed while trying to cross the road,” said Cassady St. Clair. “However, we reasoned that they have to do this anyway as part of living beside a highway and we wanted to know how hard it is for them to cross. They appear to be pretty good at it. Not a single animal died in the two years of study and those that were not able to return on their own were captured and returned by Wayne.”

The bottom line, says Cassady St. Clair, is that small covered culverts, which offer protection from other animals, are better for these tiny mammals. The research has already caused one of the paper’s referees, who had offered expert opinion on some new road construction, to change his instructions to the builders–asking for more culverts.

“Overall, the paper has some potential to help people appreciate that conservation involves more than big furry animals and that some quite affordable mitigation can also be quite effective for small animals,” said Cassady St. Clair.