Deaths of two mountain lions blamed on use of rodent poison

Dead cougars were found in Simi Hills

News Home Page                Home Page

Source of this article - Thousand Oaks Acorn, February 10, 2005.

By Daniel Wolowicz, Special to The Acorn

Within the past three months, two mountain lions were found dead in the Simi Hills.

The two carnivores—a female known as P4 and a male called P3 —were among the wildlife tracked by National Park Service naturalist Seth Riley in a recent study. His research found that suburban development and pest control substances cause problems for wild animals in the local habitat.

Riley, a wildlife ecologist for the Santa Monica Mountains National Recreations Area, recently addressed a standing-room-only crowd at the National Park Service Visitor Center in Thousand Oaks.

In his lecture "Carnivores on the Fringe," he presented the results of his nine years of field research on the impact of urbanization on large carnivores.

Hosted by the NPS, the lecture was part of a series that lets the public speak directly with scientists, said Park Ranger Sheila Braden, the event's coordinator.

Riley's talk focused on bobcats, coyotes and mountain lions. His fieldwork on bobcats and coyotes was done primarily in the Simi Hills, while he tracked the mountain lions throughout the Santa Monica Mountains, the Simi Hills and the Santa Susana Mountains.

Specifically, Riley noted how major freeways and roadways, as well as toxic anticoagulants used in most major rodent poisons, have hurt the large carnivore population.

"The main reason for this lecture is to show people how their everyday lives affect the local wildlife," Riley said. "The simple usage of rat poison can have a complex affect on the total ecosystem, even on large cats such as mountain lions."

Using radio collars and motion sensor cameras hidden in the brush along known wildlife trails, Riley tracked animals throughout Ventura County and into the Santa Monica Mountains.

"On the coyotes and bobcats, we use basic VHF tracking collars," Riley said. "But on the mountain lions, we can use VHF collars with global positioning capability, which uploads the animal's location to a satellite on a regular basis. We can then download the information and better understand the lions' patterns."

Riley noted that the relatively new GPS technology has added a means to collect data that scientists couldn't previously have acquired.

Riley based his findings on the tracking of more than 100 coyotes, 15 to 20 bobcats, four adult mountain lions and four mountain lion cubs recently found in the Simi Hills.

The increase in urban development has brought a marked decrease in the animals' daytime movement, Riley said. In addition to the fact that these animals are primarily nocturnal, Riley thinks they curb their daytime movement to avoid human contact.

Scientists estimate 1,400 acres of natural habitat are destroyed annually to make room for urban development in the 350-square-mile Santa Monica Mountains, according to the Los Angeles Times.

"In some cases, these animals end up living in habitats totally surrounded by developed land," Riley said.

Because large predators require an enormous amount of space to find food and mates—an adult male mountain lion prowls about 300 square miles—Riley said many of the animals cross busy roads or freeways on a regular basis.

However, highways aren't the primary reason so many large carnivores die prematurely, according to Riley.

Within a group of tracked bobcats, 28 died. Of those deaths, vehicles killed only six. There were 18 tracked coyote deaths, and only five were a result of road fatalities.

"The deaths by car are pretty low, considering how many animals we track," Riley said. "It was the anticoagulants that had a much more devastating effect on the lives of the animals."

Anticoagulants are toxins used in major rodent poisons like d-Con, which is available at hardware stores. Often used by schools, parks, golf courses, housing developments, even the National Park Service, anticoagulants are eaten by rodents and cause the blood to thin, resulting in death from massive internal bleeding. The two most common anticoagulants are bromadiolone and brodifacoum.

Rodents have developed greater resistance to the chemicals. Higher and higher doses of the poisons are required to kill rodents, which, in turn, are eaten by coyotes and bobcats. If an average-sized coyote, about 30 to 40 pounds, ingests three or four rodents over a short period of time, there's a good chance these anticoagulants will pass from the infected rodent to the coyote, killing him.

Although most felines have high resistance to the toxin, Riley said toxicology reports showed 80 percent of bobcats tested in the area had some levels of anticoagulants, and 23 of 31 studied bobcats were carrying more than one toxin.

Riley's study took a dramatic turn in the spring of 2002. A disproportionate number of bobcats were dying from what scientists thought was a form of mange, a typically non-lethal strain of the skin disease that's found primarily in cats.

A previously recorded 77 percent chance of survival from year-to-year for bobcats dropped to 50 percent in 2002 and then to only 20 percent in 2003.

Scientists realized bobcats that died of mange also had high levels of anticoagulants in their systems. Together, these two factors caused a nearly 50 percent drop in survival rates for local bobcats in a two-year period.

"We're working very hard to get this information published," Riley said. Then, he said, they'll try to let the public know "how they can make a difference."

Anticoagulants also affect the largest of the local cats—the mountain lions. Scientists suspect cougars acquire toxins from coyotes, which are one of their primary food sources.

Toxicology reports conducted by scientists from UC Davis concluded that the mountain lions P4 and P3 had high levels of anticoagulants.

Riley estimates that the Santa Monica Mountains and the Simi Hills provide enough habitat to support about eight adult mountain lions. Before the deaths ofP4 and P3, Riley's team tracked four adult lions and four mountain lion cubs. So when two of the four known adult lions died in a relatively short amount of time, Riley and his team took special note because their deaths were preventable.

Riley, who received his doctorate degree in ecology from UC Davis and is an adjunct professor at UCLA, believes there's hope for these animals.

The recent discovery of the four lion cubs heartens the ecologist.

"It's great that (the cubs) are out there," he said. "Right now, they're about 5 months old. We're really interested in tracking them after they've grown up so we can better understand where they go. That would be the next step in our study if we could find available funding."

Keeping the public informed, Riley said, coupled with efforts by Caltrans and other agencies to build animal-friendly bridges and tunnels for roadways will help maintain the wildlife population.