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Researchers believe freeway overpasses may save dwindling mountain lion population. Why are these big cats important to SoCal’s ecology?

This uncollared adult female mountain lion is
This uncollared adult female mountain lion is "cheek-rubbing," leaving her scent on a log. This photo was taken in the Verdugo Mountains with Glendale and the skyscrapers of downtown L.A. in the background.
National Park Service via Flickr

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Freeways may have made SoCal easier to traverse for humans, but they’ve also created isolated ecological zones, and subsequently isolated wildlife genetic pools, which has especially affected our small mountain lion population.

Barriers such as the I-15 and the 101 mean that these large cats are increasingly staying in one spot and interbreeding, which makes them weaker, and in the case of the males, killing each other over territory. They rarely attempt to cross freeways, but when they do, they often get hit by cars.
The solution? Researchers are pushing for wildlife crossing bridges, constructed over highways, to increase ecological connectivity.

A report from March identifies a location for an overpass above the 101 and the 15 freeways. The proposed project crossing the 101 would be a 165 foot wide overpass, constructed to the tune of $60 million, mostly privately funded. But the price tag leaves some locals wondering whether these overpasses are worth it.

What is the mountain lion’s role in the ecology of Southern California? What would be the impact of their disappearance? And what makes for an ideal wildlife crossing location?


Seth Riley, wildlife ecologist for the National Park Service at Santa Monica Mountains National Recreation Area and adjunct professor of ecology and evolutionary biology at the University of California, Los Angeles

Trish Smith, ecologist working in land protection and research in Orange, Riverside and San Diego Counties for The Nature Conservancy