Interstate Highway I-15 in Southern California Can Annihilate Mountain Lions

As human beings, we have invaded all parts of the world including forests, oceans, wildlife etc. Now, humans are yet again posing a threat to the very survival of a magnificent jungle beast – the mountain lion.A recent 13-year study at University of California confirmed that the biggest threat to Southern California mountain lions is humans. Even though hunting mountain lions is prohibited in California, humans cause more than half the known deaths of mountain lions studied. Most were killed through vehicle collisions, depredation permits, illegal shootings, public-safety removals or human-caused wildfire. Annual survival rates were only about 56%.

Exacerbating the problem is an interstate highway, I-15, a major thoroughfare connecting San Bernardino, Riverside and San Diego counties that has proven nearly impossible for the mountain lions to cross. Crossing the interstate, especially for the animals of breeding age, is important for this population's declining genetic diversity and long-term health and survival.

Most of the available mountain lion habitat in Southern California is sandwiched between the greater Los Angeles and San Diego areas, home to a growing population of about 20 million people.

Lead author Winston Vickers, an associate veterinarian with the UC Davis Wildlife Health Center at the UC Davis School of Veterinary Medicine, said fragmentation of mountain lion populations by highways is happening to a serious degree in the Santa Ana mountain range, as well as elsewhere in Southern California, such as the Santa Monica Mountains. In the Santa Anas, fragmentation and genetic restriction are compounded by unusually low survival rates. This raises significant concerns about the future persistence of this population.

Vickers said. "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."

During the 13-year study, the researchers detected only one mountain lion that made it across I-15 moving east to west, the direction needed to improve genetic diversity for the Santa Ana Mountains population. That male lion, M86, successfully bred and produced at least four offspring before he died. Of those four, one was poisoned, one was hit by a car, and another was taken into captivity for being too familiar with people. The fourth lion produced kittens, two of which she raised to adulthood, and one of which, F126, is known to still be alive.

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"So all the genetic hopes of this population may be pinned on this one animal, F126 -- a female we know is circulating," Vickers said. "Given the odds of that female producing kittens, and those kittens producing kittens, it will take generations and generations to see if his effort, M86's, in crossing the road was worth it."

The situation for mountain lions in the Santa Anas, particularly, has become so dire that translocation such as was done for the endangered Florida panther may be necessary to prevent further genetic decline, the study warned. However, developing means to connect the population more naturally is preferable, Vickers said, such as by creating safe crossings along targeted highways.

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"This population has one foot on the banana peel and one foot on the edge," Vickers said of Santa Ana mountain lions. "Whatever we can do, we should do. Other populations are going the same direction, they're just not as far down the road."

Source-Eurekalert