Where Have All The Bobcats Gone?

New research points to rat poison as a culprit in the animals’ decline

2010-08-26
By RENNIE CHAMBERLAIN

Special to the Palisadian-Post

Laurel Klein, wildlife biologist and UCLA graduate student, carries a tranquilized bobcat captured in the Santa Monica Mountains for study. Assisting her is Tiffany Teng, former UCLA undergraduate in biology. Photo courtesy Laurel Klein

For the past dozen years, the National Park Service has been tracking mountain lions, coyotes and bobcats in the Santa Monica Mountains to study how these animals are adapting to the urban environment, gathering data on genetics, diet, movement patterns, number of kittens, size of home ranges, and mortality rates.

??Laurel Klein, a wildlife biologist and UCLA graduate student, is at the forefront helping the Park Service with its study of bobcats.

??In 1997 the bobcat survival rate was about 84 percent.’ In 2002, there was a sharp decline, and by 2003 the survival rate had dropped to 28 percent.

??Klein wants to know why the bobcat population is declining and why the cats are behaving so erratically, wandering onto freeways and into backyards in broad daylight.

??Klein and the Park Service believe the culprit is a special kind of mange, an ectoparasitic disease called notoedric mange. Oddly, notoedric mange does not usually attack wild cats. And mange alone does not kill normal animals.

??Heading out to Thousand Oaks where the NPS has trapped a bobcat, my friend Terry Matkins and I listen as Klein discusses the recent decline in bobcat numbers. On our way we pass a dead coyote on the road, and Laurel hopes it will be there when we return. Not only can she use the coyote fur in her traps, but she will also check the coyote’s liver for anticoagulants.’

??Anticoagulants, a main component in rat poison, have become a big problem in the area, especially for carnivores. The substance is everywhere, around homes, public parks, public buildings, golf courses, landfills, farms and gardens.’

??Since 1996 the Park Service has gathered blood and tissue samples from more than 190 cats that have died.

??Before 2000, there were no bobcat deaths due to mange, and the population was holding steady.’ Then in 2001, one bobcat was found dead from mange. In 2002 it was eight, and in 2003 it was 10.’ The Park Service began doing necropsies on the dead cats and found that in 90 percent of the cats with mange, there were also high levels of anticoagulants in the liver. This was also true for coyotes and mountain lions.

??But why this sudden increase in anticoagulants?’

??The answer is simple. By 2002, a new generation of rat poisons was on the market.’ Before that, Warfarin was the main ingredient in rat poisons, but eventually the rats developed a genetic resistance to it. Companies then began creating compounds known as second-generation anticoagulants that were longer lasting and more potent.’

??These new anticoagulants have become a problem for wildlife because the poisons are stronger. Unfortunately, they are advertised as safe to use outside the home and people use them and they do the job.

??Although there are few studies to document how non-target wildlife is affected by the anticoagulants, it is known that the poison moves up the food chain: the bobcat eats the poisoned rat, or the mountain lion eats the dead coyote that has eaten the poisoned rats. ‘

??One might think that as the poison travels from one animal to the next it would become diluted, but the opposite is true.’ The potency of the poison increases because the poison doesn’t act immediately. The first dose is lethal, but because it takes several days to act, the rat has plenty of time to ingest more poison. It’s the same with the coyotes and bobcats.’ The more rats they eat, the weaker they become, thus the more rats they continue to eat because the poisoned rats are easy prey for a weakened carnivore.’

??On the whole, bobcats appear to be quite tolerant of anticoagulants. Necropsies performed on dead bobcats show that the cats have been exposed multiple times to multiple anticoagulants before they end up dying from a secondary cause, usually mange.

??These multiple exposures mean the cats are getting one brand of poison from around a home and a different brand of poison from a golf course. And because the animals are now living in an urban environment where their home range has become extremely restricted, they continue to hunt in a very small area, typically a golf course or along edges of wilderness between housing developments, where they continue to ingest the poisons.’

But what do all these new anticoagulants have to do with bobcats dying of notoedric mange?

??Of the 19 bobcats that died of mange between 2001 and 2003, all of them were exposed to anticoagulants and 17 of them were exposed to levels as low as .05 parts per million. This small amount is all it takes to compromise a bobcat’s immune system, making it weak and susceptible to mange, as well as affecting its behavior.

??One cat that was strong and had lived in the area for a long time, three or four years, became exposed to anticoagulants and began changing his activity patterns. Ultimately, he became so disoriented he wandered onto the 101 Freeway and was killed.’ By that time he was emaciated and had a severe case of notoedric mange. ‘

??Although there’s still much to learn, scientists have pinpointed many contributing factors to the bobcat population decline: loss of habitat; the fragmentation of home ranges; increasing urban developments; and shrinking genetic pools. As for the mountain lions and coyotes, the anticoagulants have been a direct source of mortality instead of a secondary source such as mange.

??As Klein drops us back at Topanga Park and heads off to take her samples to UCLA for processing, I find myself wondering what is it going to take to make people realize that their desire for the cheap, easy fix can have devastating results? The irony, of course, is that in our insistence on using convenient poisons we are killing the very predators that help keep the rodent population in check, as well as endangering our own health and the health of our pets.’

??Bobcats are solitary animals and their dying happens in secret. Few of us even know it is happening.’ But if we need a clearer picture of what our desire for the cheap, easy fix is doing to our wildlife and our environment, we need look no further than the oil spill in the Gulf of Mexico.

??For more information, visit urbancarnivores.com

(Rennie Chamberlain serves on the advisory board and Terry Matkins is the wildlife photographer for The Nature of Wildworks, a Wildlife Care and Education Center in Topanga. Both are Pacific Palisades residents.)

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