With rising human population growth and development, maintaining wildlife connectivity can be a significant challenge. Road creation and expansion, along with increasing vehicle traffic, is responsible for fragmenting wildlife habitat and causing significant direct mortality. As an expanding human population strives to increase its own connectivity, the task of reducing wildlife mortality from roads and promoting wildlife access can be a daunting task.
Fortunately for wildlife, many nations are working to increase connectivity, improve road construction, and take steps to protect vulnerable wildlife. Indeed, a new field of conservation study, road ecology, has emerged, and one of the most critical components its practitioners are tackling is connectivity. Parks Canada, a primary and founding partner in the longest running wildlife crossing study in the world1, has much to contribute to this emerging field of science, while helping to lead the way in applied innovative solutions to wildlife connectivity.
In Waterton National Park, roadway mortality had suddenly spiked for a local population of threatened Long-toed salamanders. It was determined that a significant contributor was a new 10cm curb along the roadway which trapped the small amphibians on the roadway. A new sloped curb helped reduce mortality temporarily, but over time an increase of roadway traffic reversed these initial gains. The definitive solution was to install special light and water permeable crossing-culverts with intercept fencing to guide long-toed salamanders and a host of other small animals including tiger salamanders, western toad, snowshoe hare, red squirrel, mouse, chipmunk, vole, skunk, and racoon under the roadway. In Jasper National Park, two major highways, 6 additional paved secondary roads, and a host of tertiary gravel roads that service trailheads, utilities, and the Canadian National railway line have created a diverse network of barriers across hundreds of small, and not so small streams and creeks. Many of these waterways have prevented fish, amphibian, and aquatic mammal passage for over half a century. On a prioritized basis, these crossings are now being replaced or repaired to restore aquatic connectivity. Hanging culverts are being brought down to grade, fast-flow culverts are having step pools created on the downstream end to slow flow and increase culvert water depths. In some cases, modern bridge construction replaces culverts altogether, allowing passage along the stream edge, effectively creating an additional terrestrial wildlife underpass at the same time.
There are even economic arguments to be made for Parks Canada’s increasing use of wildlife crossing structures. Kootenay National park is blazing new ground by justifying wildlife crossings for a four kilometer section of busy highway through the park using a recent North American Cost Benefit Analysis. The study found that in North America, striking more than 3.2 deer per kilometer in a single year had a greater economic cost than the infrastructure expense of the wildlife crossing mitigations for that same stretch of road. The treated highway section is expected to reduce wildlife mortality by at least 80%, a figure that has been quantified during the ongoing wildlife crossing study that was started in neighboring Banff National park1.
Banff National park is a world leading site for innovative crossing structure design as well as research and monitoring of their effectiveness. Parks Canada first implemented fencing and wildlife crossings in 1996 when a significant upgrade to the Trans Canada highway was being implemented and to date, has installed 39 wildlife underpasses and six wildlife overpasses along an approximately 100 km section of fenced and twinned Trans-Canada highway. Many important discoveries have resulted from the year-round monitoring program of these crossing structures. It has been learned that when given a choice, different large mammals prefer certain crossing structures. Grizzly bears, wolves, elk, moose and deer prefer crossing structures that are high, wide, and short in length, while black bears and cougars tend to prefer long, low, and narrow underpasses. Research has also found that there is a learning curve for wary species to begin to trust and use wildlife crossings; grizzly bears for example took five years before they started using these wildlife overpasses. It was over a decade before wolverine or lynx were finally recorded using an underpass. Research enabling adaptive management continues, and projects like DNA sampling from target species using barb wire snares placed to catch wolf and grizzly passage, continues to provide valuable information on genetic continuity and population dynamics.
Perhaps the most important lesson from Parks Canada’s use of different wildlife crossing structures is the importance of applying mitigations that are appropriate to the animals you are trying to assist. Sometimes, the solution can be as simple as selecting the proper sizing and placement of a culvert during road construction, but if necessary, even a six lane, trans-national freeway can be made safely permeable for wildlife.
For some excellent images and examples of crossing structures used in Banff National Park, check out the interactive map at http://highwaywilding.org/viewer/
Huijser, M.P, J. W. Duffield, A.P. Clevenger, R.J. Ament & P.T. McGowen. 2009. Cost-benefit analyses of mitigation measures aimed at reducing collisions with large ungulates in North America; a decision support tool. Ecology and Society 14(2): 15. [online] URL: http://www.ecologyandsociety.org/vol14/issue2/art15/.