Puma and Southern California: Human Predators and a Highway

Mountain lions in Southern California have a predator that is sometimes tall, sometimes short, and drives cars along Interstate-15.

It turns out that humans cause more than half the known deaths of mountain lions (Puma concolor) in the highly populated counties near the Santa Anna Mountains, according to a 13-year study by the University of California Davis, which the researchers reported recently in the journal PLOS ONE.

The study combined genetic and demographic data, determining that in a state where hunting mountain lions is illegal, humans still caused more than half the deaths of the mountain lions studied. Most died through vehicle collisions, depredation permits, illegal shootings, public-safety removals or human-caused wildfire. Annually, the studied cats' survival rates were about 56 percent, said a release.

The I-15 between San Bernardino, Riverside and San Diego counties was a major factor, proving nearly impossible for mountain lions to cross. In order for the cats to increase genetic diversity, it's important for animals of breeding age to cross the highway, the release noted.

"Nowhere in the U.S., outside of the endangered Florida panther, have mountain lion populations been documented that are this cut off and with survival rates this low," lead author Winston Vickers said, in the release. "This means that the odds of an individual animal making it across I-15, surviving to set up a territory, successfully breeding, and then their offspring breeding so the genes are spread throughout the population is harder to have happen naturally than one would expect."

Scientists think that translocation -- such as was done for the endangered Florida panther -- may be necessary to prevent further genetic decline. However, they would prefer to create safe crossings along targeted highways, the release said.

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