Does a Bear Cross the Road in the Woods? Study Says Yes.
In a study that could have implications for California, an expensive set of wildlife crossings in a Canadian national park are in fact being used by the animals they were built for.
The Trans-Canada Highway winds through Banff National Park in Alberta, Canada for about 80 miles. Over much of its length, the Highway is a divided high-speed four-lane that poses a serious risk to animals attempting to cross it. In the 1990s the Canadian government installed a number of wildlife crossings in the park, some of them elaborate, vegetated overpasses, to provide animals safe access to habitat across the highway.
A study published Wednesday indicates that some of the park's largest, most endangered wildlife -- including the beleaguered Alberta grizzly bear -- is indeed using the crossings. And not just for foraging: genetic testing shows that the wildlife crossings are allowing grizzly and black bears to find mates on the other side of the road.
Banff's network of wildlife crossings is the most extensive in the world, with 44 crossing points ranging from simple culverts to broad, vegetated overpasses like the one shown above. Researchers Michael Sawaya, Steven Kalinowski, and Anthony Clevenger of Montana State University at Bozeman installed hair collection snags across the crossings, essentially a strand of wire that collected samples of fur from black bears and grizzlies availing themselves of the over- or underpasses.
They then compared the genetic makeup of those samples with three years' worth of samples from the bear population on both sides of the Trans-Canada Highway to determine whether the bears using the crossings were mating successfully. And the results, published Wednesday in the Royal Society's biological journal "Proceedings B," showed that black bear genes now move across the highway as though the road wasn't even there. Almost half -- 47 percent -- of black bears using the crossings mated successfully.
Grizzlies are apparently helped less by the crossing network: of the big bears using the crossings, only 27 percent bred successfully. But even the grizzlies' lower cross-road breeding success rate is enough to forestall reproductive isolation due to the road, which means less chance that the already beleaguered bears, listed as Threatened by the Alberta provincial government, will suffer from inbreeding.
One male black bear was so enthusiastic about the broader horizons offered by the crossings that he sired 11 cubs with five different female bears during the course of the study. And Sawaya suggested in an interview with the science website phys.org that grizzlies' success rate may climb once the bears get used to the crossings, especially if mothers instruct their cubs in the finer points of using them.
Wildlife crossings are big news in California these days. A proposed $10 million crossing of the Ventura Freeway in the western San Fernando Valley may be crucial for the long-term survival of mountain lions in the Santa Monica Mountains, as we've reported on a few occasions. Route 17 through the Santa Cruz Mountains is another bad place to be a puma crossing the road, with at least six reported fatalities in the last few years between Los Gatos and the summit.
Mule deer and black-tailed deer are another large mammal that often falls victim to California road traffic. And as the California Wildlife Crossing site shows, California has its own issue with black bears failing to cross highways successfully.
Until this week's paper was published, wildlife managers had essentially been working on common sense in advocating for better wildlife crossings: little study had been done on the actual benefits to genetic connectivity the crossings could provide. It's always risky to extrapolate from one group of animals in one place to different species in a wholly different place, so the Banff study may not apply directly to all California wildlife.
But still: it's data we didn't have, and that's likely to help bolster arguments for making our highways safer for wildlife.