Bears Use Wildlife Crossings to Find New Mates
By Tanya Lewis, Staff Writer | February 18, 2014 07:01pm ET
 Grizzly bear family using metal culvert |
underpass.
Now, a team of researchers at Montana State University has compared the genetics of grizzly bears and black bears at road crossings in the Canadian Rockies, finding the bears do indeed move across the Trans-Canada Highway, and breed with mates on the other side.As more and more roads cut across the territories of wild animals, wildlife crossings are being built to bridge these barriers. But there has been little evidence that animals actually use the crossings.
The study provides the first proof that wildlife crossings maintain genetic diversity, the researchers say. [Photos of Grizzlies & Black Bears Crossing the Highway and Bear-Crossing Video]
"Roads connect human populations, but fragment wildlife populations," wrote the authors of the study, detailed today (Feb. 18) in the journal Proceedings of the Royal Society B.
Busy roads can lead to deaths or deter animals trying to cross the pathways. This prevents gene flow — the transfer of genes from one population to another — reducing genetic diversity and making it harder for the animals to adapt to a changing environment.
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.
The team noted that grizzlies have used crossings at a growing rate between 1996 and 2008, probably in part because bear cubs learned the behavior from their mothers. The study also found that male bears that used the crossings most often had the highest reproductive success
of males that crossed, suggesting crossings increased the number of opportunities for the bears to mate, though the researchers say more studies are needed.
of males that crossed, suggesting crossings increased the number of opportunities for the bears to mate, though the researchers say more studies are needed.
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Editorial
Make the Ventura Freeway safe for mountain lions too
The big cats essentially live on an island — hemmed in by freeways and the ocean — and their isolation imperils their long-term survival. A wildlife crossing is needed.
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P-32 is one of three mountain lion kittens born in the Santa Monica Mountains in December that appear to be the result of inbreeding. (National Parks Service / January 8, 2014)
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Los Angeles may be densely inhabited and full of traffic, but residents here are lucky to live near wild open spaces large enough to sustain mountain lions. About a dozen adult mountain lions live, mate and hunt deer and small prey on a patchwork of public and private land in the Santa Monica Mountains stretching from Point Mugu to the Sepulveda Pass. But these big cats essentially live on an island — hemmed in by freeways and the ocean — and their isolation imperils their long-term survival.
Over a decade, the National Park Service has put GPS collars on about 30 mountain lions in the Santa Monica Mountains, giving biologists new insight into how the area's last large carnivores survive on the urban edges. The research has shown that L.A.'s roads and sprawl not only make it nearly impossible for young male cats to move into new terrain to avoid clashes with larger males, but also that they lead to inbreeding.
Indeed, three kittens born in the Santa Monica Mountains in December were the result of inbreeding. Of the six litters tracked by the Park Service in recent years, half were produced by the father mating with his offspring. Inbreeding over time can lead to heart problems and defective sperm, and threaten the viability of the local population. Last fall, a mountain lion from the north that could have introduced new genetic material was struck by a car and killed while trying to cross the 101 Freeway in Agoura Hills. In the last decade, biologists have tracked just one mountain lion that was able to make it across the 101. The road is considered the biggest barrier to restoring the genetic diversity that the mountain lions need.
The solution is to build a wildlife crossing at the Ventura Freeway, which would benefit many kinds of animals but especially mountain lions. For years, the Park Service has pushed for a $10-million, 13-by-13-foot tunnel at Liberty Canyon Road in Agoura Hills. This is the rare stretch where there is parkland on both the north and south sides of the freeway, which is required for a wildlife crossing. But the agency's applications for federal funds have been rejected in favor of other projects. Now, the Santa Monica Mountains Conservancy will consider next week whether to provide $200,000 for Caltrans to study the feasibility of building a wildlife crossing at the Lost Hills exit on the Ventura Freeway(101).
Whether over or under, it's clear that a crossing is needed to help the mountain lions survive and thrive. One of Los Angeles' greatest assets is its proximity to nature, and it's amazing that large predators can still roam the hillsides of the nation's second-largest city. State and local leaders need to invest the money to ensure that mountain lions remain in the Santa Monica Mountains.
Whether over or under, it's clear that a crossing is needed to help the mountain lions survive and thrive. One of Los Angeles' greatest assets is its proximity to nature, and it's amazing that large predators can still roam the hillsides of the nation's second-largest city. State and local leaders need to invest the money to ensure that mountain lions remain in the Santa Monica Mountains.
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