Talk tackles future of local mountain lions in Santa Monica Mountains

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The population of mountain lions in the Santa Monica Mountains is on the decline due to loss of habitat. Photo courtesy of the National Park Service

Nearly 200 people came to King Gillette Ranch Saturday to hear scientist Seth Riley speak about the increasing challenges faced by mountain lions, bobcats and coyotes due to urbanization. 

Among the topics covered were habitat fragmentation due to roads and highways and the lethal impact of rat poison on local carnivores as the Santa Monica Mountains grow increasingly populated. 

Riley, in association with the National Park Service and UCLA, has been studying local populations of wild coyotes, bobcats and mountain lions for nearly 15 years. National Geographic magazine is doing a major article on research Riley has been conducting on mountain lions, which is expected to be published by the end of 2013. 

“I’m interested in the challenge of preserving wildlife in urban areas,” Riley said. Urban carnivores are a particular conundrum, he said, “because they need a huge amount of space and would be the most affected by urbanization and fragmentation.” 

Asked for a show of hands, nearly everyone in the audience Saturday indicated they had seen last week’s photo of a mountain lion dragging a deer it had killed off Mulholland Highway and into the woods as a cyclist unwittingly rode by. 

The photo captured a key problem facing carnivores in the Santa Monica Mountains: the large territories they require, which are now divided by roads. 

“The first male we studied used the entire Santa Monica Mountains as his home range— 400 square kilometers,” Riley said. “The females have smaller ranges, maybe 100 square kilometers.” 

Among the 31 mountain lions the National Park Service has tracked with collars, only one has successfully crossed the 101 freeway in the past 15 years. The 101 and 405 freeways are barriers to their movement, along with farming and development all around the edges of the mountains, making the area essentially an island for the big cats. 

This barrier has given way to a major problem of inbreeding due to isolation. 

“There are fewer than 10 mountain lions in the Santa Monica Mountains, which is not enough for a genetically diverse population,” Riley said. “They have the lowest genetic diversity of any mountain lion population in the state.” 

The creation of a wildlife corridor between the Santa Monica Mountains and the Simi Hills that would allow mountain lions and other wildlife to safely cross the freeways has been a dream of Riley and his fellow researchers. However, despite identifying the exit at 101 and Liberty Canyon Rd. as a good spot to build a wildlife crossing due to it being one of the rare highway interchanges with natural areas on both sides of the freeway, a recent Caltrans estimate showed that building a tunnel would cost a prohibitive $10 million. 

Residents in the Liberty Canyon area who attended the talk suggested closing the Liberty Canyon interchange altogether, which drew wide applause from the audience. 

One of Riley’s most significant findings during his research is that the use of anticoagulant rodenticides, commonly known as rat poison, has had far reaching impacts on the local populations of urban carnivores. 

Rather than dying immediately, rodents that ingest poison put out by homeowners and pest control companies simply slow down first, Riley said. In the meantime they become easy prey for coyotes and other predators, which may eat a number of infected rodents before the level of toxins finally becomes lethal. 

Of 60 coyotes collared and studied, 12 died from rat poison, which causes them to bleed to death internally, Riley said. Riley displayed gruesome photos of dead coyotes lying in pools of their own blood after eating too many rodents that had ingested the poison.

Cats react somewhat differently to rat poison. Researchers conducted blood and liver tests showing that 90 percent of the bobcats tested had been exposed to more than one rodenticide. The poison or “toxicant” tends to lower their resistance to disease, which can result in a form of mange. 

“They have a crusty face and head, and become emaciated,” Riley said. “A significant number of mortalities and declines in population have been noted in bobcats” in the Malibu area because of rat poison, he said. Two of the 31 mountain lions studied so far had died directly from rat poison, both of which had killed and eaten coyotes in the previous month. 

Riley mentioned Malibu’s recent successes in getting local merchants to stop selling rodenticides, and said the city of Calabasas is also looking into it. 

Riley’s talk took place at the new visitor’s center of the King Gillette Ranch. For more information on upcoming events at the visitor’s center, call 818.878.0866 ext. 228.