The effects will only worsen with climate change, the researchers added.
Wildlife biologist Michael Sawaya of Montana State University and his colleagues conducted a three-year study of grizzly (Ursus arctos) and black bears (Ursus americanus) at Banff National Park, Canada, to test how effectively wildlife crossing structures actually bridged bear populations.
The researchers set up barbed-wire hair traps on highway underpasses and overpasses, and sequenced the DNA from fur left behind by passing bears. The scientists compared genetic data from the wildlife crossings with data from bear populations in surrounding areas.
Results showed a genetic discontinuity - a division between two distinct populations - at the Trans-Canada Highway for grizzly bears, but not for black bears. Genetic tests revealed that 47 percent of black bears and 27 percent of grizzly bears that used the crossings (including males and females) bred successfully.
The findings are good news for bears and other animals whose territories are increasingly divided by highways. "It is clear that male and female individuals using crossing structures are successfully migrating, breeding and moving genes across the roadway," the researchers wrote.