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Mountain Lions Are Killing Each Other & Inbreeding Because They're Trapped By The 101 Freeway, Study Says

This mountain lion, named P-22, was the only one in the past decade to successfully migrate out of the Santa Monica Mountains over the past decade (Photo courtesy of National Park Service)
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Researchers are finding that the mountains lions living in the Santa Monica Mountains are exhibiting some bizarre behavior—like heavy inbreeding and killing each other off. And it looks like it's because the animals are isolated and trapped in by the surrounding freeways, namely the 101.

The Cell Biology journal released a study today about how there's alarmingly low genetic diversity among the mountain lions south of the 101 Freeway. After studying 42 cougars in the area, they found that prior to 2009, the genetic diversity was lower than any other population in all of North America, except for southern Florida. And they've found a number of instances of father and daughter inbreeding, as well as some abnormal behavior like mountain lions killing their own mates, siblings and children.

Since the mountain lions are blocked off by the 101 Freeway to the north, the 405 Freeway to the east, and the Pacific Ocean to the South, it's hard for them to leave their area to mate with other mountain lions in different parts. City Lab reported that with the 175,000 vehicles that travel through the 101 everyday, it's nearly impossible for the felines to cross over.

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The colorful dotted areas are where the mountain lions live. The Santa Monica Mountain lions are trapped in between the 101 and 405 freeways (Image via National Park Service)
Seth Riley, a researcher behind the study, told City Lab that young male lions usually leave the nest when they're about 12 to 18 months old. However, since it's difficult to migrate out of the Santa Monica Mountains, they're forced to stay. “It’s typically advantageous for male lions to fight, kill, or run off other males," Riley said. "But in a normal situation, every male disperses... What ends up happening is you have these interactions that shouldn’t be happening—fathers are killing their sons and vice versa."

This is definitely a red flag for researchers, and Caltrans is planning on building a bridge over the 101 Freeway to help the mountain lions cross over. A number of lions have been killed crossing the freeways and this would provide them with a safer alternative.

It's not to say that mountain lions haven't ever successfully escaped the Santa Monica Mountains, though it's rare. One lion, dubbed P-22, made the trek over to the Griffith Park, and was the first in a decade to do so, Santa Monica Observer reported. He was made famous after a National Geographic photographer snapped a breathtaking image of P-22 walking in front of the Hollywood sign.