Planet Earth

Bears Use Highway Crossings to Find Mates

D-briefBy Gemma TarlachFeb 19, 2014 3:38 PM

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Finally, there's proof: If you build it, they will cross. As highways and other roads have stretched deeper into once-remote corners of the planet, building wildlife crossings has become a common way to preserve migration routes and prevent population isolation for a variety of species. One problem: there was little data showing the crossings actually work. A new study, however, has provided the first evidence that they do. Crossings built over and under a major highway in Banff National Park are being used by the surrounding grizzly and black bear populations, and are in fact preserving the bears' genetic diversity, as intended.

A Road Runs Through It

Researchers based their study on the Bow Valley area of Banff National Park, bisected by a stretch of the Trans-Canada Highway that had been widened from two lanes to four in the '80s and '90s to accommodate increased vehicular traffic through the popular park. During the expansion project, crews built two overpasses and 23 underpasses to facilitate the movement of wildlife north and south of the highway. Over a three year period beginning in 2006, researchers studied grizzly and black bear DNA samples in the area, collected either through hair snags from 20 of the wildlife crossings or hair snags and bear rubs from sites both north and south of the highway. (And no, in case you're wondering, a bear rub sample is not obtained by some lucky research assistant sidling up to a grizzly with a friendly smile. The animals often rub their backs against trees and other objects to leave scent-based messages for other bears in the area; in doing so, they often leave behind stray hairs that can be used for DNA analysis.)

Moving and Mating

From the nearly 10,000 samples collected, researchers were able to identify 113 individual grizzly bears and 101 black bears. The team found genetic evidence that bears of both species were using the crossings to migrate in both directions. They also found DNA from cubs that had been born to those bears. Both elements were important finds, because migration on its own is not conclusive proof that the crossings protect genetic diversity. According to the research team, 15 grizzlies and 17 black bears were identified from crossing sites. Eleven of the grizzlies and six of the black bears were identified from samples both north and south of the highway; several of the animals had successfully bred. This may seem like a small percentage of the overall population, but the researchers claim the amount of migration is more than enough to ensure populations on both sides of the highway remain genetically connected and are not isolated. The research, published in the Proceedings of the Royal Society B, is good news for the animals. It's also good news for us: the pace of human development worldwide shows no signs of slowing.

Image by Jean-Edouard Rozey / Shutterstock

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