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Southern California mountain lions face possible extinction, study finds

by in News

Hemmed in by freeways isolating them from larger populations nearby, the mountain lions of the Santa Ana and Santa Monica mountains face a moderate to near-certain chance for extinction in the coming decades unless new cats find a way into the ranges, according to a study published today in the journal Ecological Applications.

Only once before have researchers recorded a mountain lion population with so little genetic diversity as these two Southern California “habitat islands.” Small populations, a lack of immigration by outside lions and inbreeding all contribute to their precarious status.

“These are higher extinction probabilities than any of us would like to see,” said the study’s lead author, University of Nebraska wildlife ecologist John Benson. “If we are not able to increase movement of mountain lions between these isolated mountain ranges and adjacent areas occupied by lions, we should not be surprised if local extinction occurs in these two small populations at some point in the future.”

While plans are afoot for freeway “wilderness crossings” to help entice immigration by other lions, actual construction of such a pathway remains uncertain.

  • This Nov. 2014 photo provided by the National Park Service shows the Griffith Park mountain lion known as P-22. The photo taken by a remotely triggered camera set up at the site of a freshly killed mule deer. Photo courtesy of the National Park Service.

  • The National Park Service discovered four new mountain lion kittens in the Santa Monica Mountains. On Tuesday, Sept. 4, 2018, the agency released images of P-70, P-71, P-72 and P-73. Their mother is P-19, and their father is P-56, who is P-19’s own grandson. This is P-19’s fourth litter. Photo courtesy of the National Park Service.

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  • P-19. an 8-year-old female mountain lion in the Santa Monica mountains, gave birth to four kittens in early August 2018. Photo courtesy of the National Park Service.

  • This overview of Liberty Canyon shows the area where three male mountain lions crossed into the Santa Monica Mountains, at least one of whom mated and brought fresh genes to the range. This is also the area where environmentalists would like to build a $60 million wildlife bridge to facilitate immigration by lions and other animals. Photo courtesy of the National Park Service.

  • A still photograph from a motion activated camera shows mountain lion M86. The now-deceased male is the only lion since at least 2001 known to have crossed Interstate 15 from the east and mated on the west side, bringing fresh genes into the highly inbred population of the Santa Ana Mountains. Photo courtesy of the Irvine Ranch Conservancy.

  • This south-facing view of Interstate 15 in Temecula shows the area at least three mountain lions are believed to have crossed over the past 15 years, at least one of whom brought new genes into the population west of the freeway. A study is underway to develop possible wildlife crossings in the area to help ensure the long-term viability of lions in the Santa Ana Mountains. Photo courtesy of the UC Davis Wildlife Health Center.

  • This mountain lion, known as P-45, is one of three lions to have crossed the 101 freeway into the Santa Monica Mountains, bringing fresh genes. Photo courtesy of the National Park Service.

  • The mountain lion known as P-22, shown here dining on a deer carcass, was born in the Santa Monica Mountains and crossed the the 101 and 405 freeways to make an unlikely home in Griffith Park. Photo courtesy of the National Park Service.

  • A mother mountain lion, known as F92, keeps watch as her kittens, F126 and F127, dine on a deer in the Santa Ana Mountains in 2014. All three cats are the offspring of M86, the only known cougar to cross Interstate 15 and mate on the west side of the freeway since at least 2001. He brought much needed fresh genes into a dangerously inbred population. Photo courtesy of the UC Davis Wildlife Health Center.

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A $60-million wildlife bridge over 10 lanes of Freeway 101 at Liberty Canyon in Los Angeles has been designed, but it’s far from ready for groundbreaking. Fundraising for the Santa Monica Mountains project, begun in 2015, has been steady but slow, with $7.7 million raised, according to the #SAVELACOUGARS coalition raising the money.

To help the lions in the Santa Ana Mountains, students and faculty at Cal Poly Pomona developing alternative plans for a crossing of Interstate 15, in Temecula, with proposals to be unveiled in late April or early May. The Nature Conservancy spent $1.7 million to buy 73 acres next to the freeway for use as part of a crossing, but there is no fundraising yet for construction.

Famous cats

The Santa Monica mountain lions live in a habitat island of about 230 acres bordered by freeways and the Pacific Ocean. There are an estimated seven adult lions there — five females and two males — along with eight kittens and subadults, according to the study.

The small population makes the lions slightly more at risk of extinction than those in the larger Santa Ana Mountain range, which straddles the Orange, Riverside and San Diego county lines. That habitat island is nearly 600 acres with an estimated 16 adult lions — 11 females and five males — plus 13 kittens and subadults.

The most famous of the region’s mountain lions — which are also called cougars, pumas and panthers — are the few who’ve successfully crossed freeways. At the top of the list is the male known as P-22, born in the Santa Monica Mountains in 2009.

Males are more territorial than females, often killing rivals — particularly younger males — and require more turf. That leads younger males to seek out land of their own.

“Subadult males are more likely to disperse and to undertake longer and riskier dispersal events than females,” the study says.

In the case of P-22, he crossed both the 405 and 101 freeways to make his home in Griffith Park — where he’s the only cougar and isn’t breeding. Nonetheless, the Hollywood bachelor has been featured in national publications and has his own Twitter, Facebook and Instagram pages.

More significant biologically are P-12 and P-45, in the Santa Monica Mountains, and three cougars in the Santa Ana Mountains. Those are the five cats who in the past 15 years have successfully crossed freeways to bring fresh genes into those ranges.

  • P-12 crossed the 101 freeway from the north at Liberty Canyon in 2009 and has fathered at least eight litters. That initially helped diversify the gene pool, but now his genes have become part of the limited diversity and he’s begun mating with his own offspring, twice with a daughter and twice with a granddaughter.
  • P-45 crossed in the same area and was first identified in the Santa Monica Mountains in 2015. It’s unclear whether he’s alive or has offspring.
  • In the Santa Ana Mountains, M86 made it across Interstate 15 from the east, around 2011. He was found dead in 2015 and is believed to have sired 11 kittens, including a litter with one of his daughters.
  • M119 made the trip across Interstate 15 and was first identified west of the freeway in 2013. There hasn’t been a confirmed sighting of him since 2016. It’s not known if he is alive or has offspring.
  • M151 is believed to have also made the trip over the Interstate 15. He was killed by permit in 2016 after attacking domestic animals south of the Ortega highway. It’s not known if he has offspring.

While lions cross smaller roads, they rarely attempt to cross major freeways — and when they do, it can be fatal.

UC Davis veterinarian Winston Vickers, who specializes in the Santa Ana mountain lions and contributed to Benson’s study, said that records are incomplete regarding cats killed on Interstate 15, but there were four confirmed deaths from 2013 to 2018.

“Most lions we’ve tracked have just approached (Interstate 15) and not even tried it,” Vickers said. “They just turned back.”

In addition to research and coordinating work on possible crossings, Vickers has directed a series of seven-minute videos available on Youtube called “California Mountain Lions.” They include live footage of cats in the Santa Ana Mountains.

Extinction odds

Inbreeding and the lack of fresh genes is “the greatest long-term threat” to the Santa Ana and Santa Monica mountain lions, according to the study. Eventually, the loss of genetic diversity can lead to reduced birth and survival rates, a phenomenon dubbed “inbreeding depression.” That phenomenon was identified in Florida panthers in the early 1990s, as their population dwindled to 20 or 30 cats.

It was determined that the Florida panthers — the same species as mountain lions — would die off completely if nothing was done to boost the gene pool. Eight females were brought from Texas in 1995 and the population is now estimated to be 200.

There are currently no signs of inbreeding depression in the Santa Ana and Santa Monica mountain lions. However, study models predict with the current low rate of immigration, they eventually will reach a lack of genetic diversity similar to the Florida panthers when they were identified with inbreeding depression.

The Santa Ana Mountains models showed a 100-percent probability of extinction within 50 years once identified as having inbreeding depression, with the median time until extinction 12 years. The Santa Monica Mountains, with inbreeding depression, were at nearly 100-probability of extinction within 50 years, with a median time of 15 years.

But because the populations are so small — with an estimate of just two males in the Santa Monica Mountains, for instance — the death knell could come before inbreeding depression.

“Our model predicts that there is a moderate probability of extinction in these two populations over the next 50 years even before we considered genetics,” Benson said.

Benson and fellow researchers ran 5,000 scenarios for the lions in each range. Among factors taken into account were various levels of immigration, ranging from zero to one new lion annually, and mortality rates. Males killing other males is the chief cause of death in the Santa Monica range while vehicles kill the most Santa Ana mountain lions, typically on Orange County roads or on Interstate 15.

The study determined that without inbreeding depression, the lions of the Santa Ana Mountains had a 16 percent to 21 percent chance of going extinct unless immigration was increased. In the Santa Monica Mountains, largely because of the smaller population, the odds were put at 16 percent to 28 percent.

Saving the lions

While the Santa Ana and Santa Monica mountains are both believed to be at their capacity for lion populations, those capacities are small and vulnerable.

A wilderness bridge over the 101 freeway and a similar passage either over or under Interstate 15 would open those hemmed-in habitats to vaster ranges with more diverse gene pools, allowing ongoing intermingling of the two populations.

But importing mountain lions has worked in Florida in part because they had a wildlife area of 3,800 square miles to expand the population. Biologists say a similar tack is less viable for the Santa Ana and Santa Monica ranges because of the limited size of the habitats. While it would temporarily bolster the gene pool, the new genes would quickly become part of the limited gene pool — as seen in the case of P-12 — and more new lions would need to be brought in.

Mountain lions, as a species, are not endangered outside of these two areas, but the study notes the role large predators can play in ecosystems. It makes the case for connecting the lions with broader habitats nearby.

“If achieved over the long terms, this would be an important step towards maintaining intact, functioning ecosystems in these mountain ranges that lie within one of the most human-impacted landscapes in the world,” the study says.