Wednesday 7 July 2021

Green bridge for pumas traversing California's Freeway 101 will be world's biggest

NEWS AND COMMENT - LOS ANGELES, CALIF., USA: California plans to build the world's biggest animal bridge. It will traverse California's Freeway 101 which is adjacent to the Santa Monica Mountains. A conservation group is raising the $65 million to build it. It'll be called the Liberty Canyon Wildlife Crossing. It will be 65 m long and 50 m wide.

Green bridge for pumas traversing California's Freeway 101 will be world's biggest
 Green bridge for pumas traversing California's Freeway 101 will be world's biggest. Image in public domain.

The bridge will have high fencing and "sound walls" which I presume means walls which absorb the sound to make the crossing more amenable to the mountain lions. I guess they need to be encouraged to use it. 

At the moment the highway divides the habitat and distribution of the mountain lion in this area of America. When you have fragmentation of the distribution of a wild cat species like this you end up with inbreeding because the population size is too small to maintain a healthy genetic diversity. This can lead to sterile males which in turn further damages the population size.

No doubt, the conservationists have recommended this bridge as a matter of urgency. It's going to be built by the California Department of Transportation and is largely funded through private donations. Apparently, there's no state budget for it. New legislation will provide for state funding of wildlife crossings such as this one in the future. To date, National Wildlife Federation has secured $38 million.


101 Freeway carries 300,000 cars daily which presents an impenetrable barrier to mountain lions trying to cross it. When they try, they get hit by a car and killed. And to the south of the highway is the sea and to the east is Los Angeles. That's why they are trapped within this relatively small area in terms of the space required for a population of mountain lions. 

Brad Schaffer, an evolutionary biologist at the University of California, Los Angeles said that there is a large area of open space on the other side of the freeway which leads to a very large space. The bridge will allow mountain lions to have access to that space.

In addition, the density of cars on the freeway is increasing year-on-year as there are more and more people living in the area. The trouble is that the mountain lions in this area live in a 'closed population' which is causing inbreeding, declining fertility and genetic defects. Inbreeding also reduces the immune system's effectiveness.

If they lose the mountain lion in the area it will have a cascading effect on other wildlife as this cat is the top predator. There would be more deer and overgrazing depriving smaller mammals of food. He believes that the citizens of Los Angeles are "immensely proud of these lions, of having a big carnivore right in, almost in, their midst.

That is why the bridge will be built.

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