Wildlife crossing structures support demographic connectivity of bears

One of the most well-known examples of wildlife crossing structures exists in Banff National Park in Alberta, Canada.  These structures, which consist of highway overpasses and underpasses, aim to facilitate movement of species in one of the world’s largest corridors across major road barriers, in particular the Trans-Canada Highway.  After many years of use and long-term studies, methods such as camera traps have shown that the structures are traversed by a wide variety of wildlife, including large mammals such as grizzly bears, cougars, and wolves.  While these methods provide valuable information on the effectiveness of the crossings, they do little to distinguish between individuals, or provide details on individual movement, spatial and temporal patterns of use, or population-level connectivity.  In this month’s issue of Conservation Biology, researchers Michael Sawaya, Anthony Clevenger and Steven Kalinowski report on hair trapping methods used to find information on the number of male and female grizzly and black bears using the crossings, and how these numbers demonstrate connectivity within the populations as a whole.  The long term nature of the study allows them to discern population information about crossing structure use that might have otherwise been missed in the short term.  They present several encouraging results that the crossings do in fact help maintain demographic connectivity for these two species.  Relatively large proportions of the overall populations in the area (15-20% of grizzly bears, 11-18% of black bears) used the crossings.  The majority of grizzly bears detected were seen in multiple years, although it appeared that grizzly bears require time to learn how to incorporate wildlife crossing use into their home ranges.  Grizzly bears tend to prefer large, open crossings, while black bears more often used smaller, constricted crossings and are more likely adapted to a wide variety of crossings. These results, along with other temporal and spatial patterns of use, show that the wildlife crossings greatly aid the population connectivity of both species and provide greater opportunity for individual movement and genetic flow.