June 2004

Rat kills bobcat

Bobcat deaths linked to anticoagulants from rodent poison

By Jennifer Lehr

A version of this story was first published in the Topanga Messenger

On Feb. 11, I received a message on my cell phone from my husband. A bobcat had made its way to our front porch. Its skin did not hide the bones that were jutting out everywhere. Its eyes were covered with a grayish film. It ran out to the street when it saw my husband and collapsed behind the trash cans. Although my husband stood only five feet away it did not move. He called the Agora Animal Shelter and then had to leave for work.

Shaken up by his call, I called the shelter. They told me that they had turned it over to the California Wildlife Center in Malibu, who would probably euthanize it, as it was in very bad shape.

The following Saturday the bobcat was still on my mind. I called the CWC. They told me that the bobcat was a female, that she was essentially a kitten, probably born last spring, and that she was still alive, but that they did not know if she would make it.

After talking to several people at the center, including the veterinarian, I found out some alarming news. A number of bobcats, perhaps 10 of them, had been taken to their animal hospital since the summer of 2003. They had a high level of rodenticide in their bodies and most had abnormal blood clotting. They all had come in in a state of extreme emaciation; they had skin lesions and a type of mite. Except for one, caught very early, they had all died. They had most likely eaten poisoned rats, and were thus being secondarily poisoned.

In rats, the poison works slowly. It bit by bit destroys the blood’s ability to clot. For up to 10 days the rats continue to run about, ticking time bombs and easy prey, as the poison creeps through their bodies.

Seth Riley, wildlife ecologist for the National Park Service (NPS), has been studying the impact of urbanization on carnivores in the L.A. area since 1996. Carnivores, such as bobcats and coyotes, are particularly vulnerable to habitat loss and fragmentation, as they need a lot of space to survive.

Riley first studied bobcats in the Agora Hills and Liberty Canyon areas to see how the freeway was impacting them. In 1998, NPS started to radio-collar the bobcats in the Thousand Oaks and Westlake Village areas because of the amount of habitat fragmentation there. The studies included mortality, rates of survival, and movement patterns. They also looked at specific mortality causes, such as road kill and anticoagulant poisoning (rat poison).

The first bobcat NPS found that died from secondary poisoning was in the fall of 2001. The cat looked strange so they had it autopsied. It was discovered that the cat had a high level of rodenticide in his body and also had notoendric mange.

That spring at least eight more bobcats died, mangy and emaciated. At first NPS thought it was the mite epidemic, but the mite is common and very treatable in domestic cats; they couldn’t understand why it was having such a devastating effect on the bobcats.

Riley and his team had seen coyotes suffer from secondary poisoning, but bobcats, which have a higher tolerance to anticoagulants than members of the dog family, had not been as affected. The rodenticide, NPS surmised, was weakening the bobcats’ immune systems, making it impossible for them to fight the mange.

By some estimates 19 cats have now died emaciated and with mange. Of course, these are the animals that have been found by people; others have probably died without being found. The only cat that survived was discovered by NPS officials as it was being radio-collared; they saw that it showed early signs of mange and were able to treat it with vitamin K (which helps the blood clot) and mange medicine. All but one of the 19 had a very high amount of anticoagulant poison in their bodies (determined through either a liver biopsy or a blood test).

Brodifacoum, the chemical in widely sold poisons D-Con, Talon, and Havoc, is designed to be used only inside a structure. However, these poisons are being put outside, not just by individual homeowners, but also at office parks, by homeowners associations at condo complexes, in soccer fields, etc. At one point the Calabasas landfill was using it, although they have since stopped. Even if used inside, the rats can leave the structure and wander about outside.

Brodifacoum is absorbed through the gut and inhibits vitamin K–dependant steps in the synthesis of multiple clotting factors. Death usually occurs through gastric hemorrhage. It is very toxic to mammals and birds.

Diphacinone is another common rodenticide. It is an ingredient in Diphacine, Ditrac, Gold Crest, Kill-Ko, P.C.Q., Promar, Ramik, Rat Killer, Rodent Cake, and Tomcat. It works by the inhibition of liver-synthesized coagulation proteins, leading to internal hemorrhaging.

For coyotes, death is similar to the rats. Their inner cavities fill up with blood. According to Molly Hogen, of Nature of Wildworks, hawks and owls, species that feed on rodents, also die of secondary poisoning. She described their deaths as horrible and slow. The poison would have a similar effect if eaten by domestic animals.

The little bobcat that my husband had found died the following Wednesday. Although she had started eating, her body temperature never stabilized.

The few times I have seen bobcats in Topanga have been amazing and magical. Walking up Observation Drive one day, my husband and I watched one for several minutes before it saw us and disappeared into the brush. That we have other creatures living in these mountains with us is one of the reasons I want to be here.

Even over the week between the bobcat’s death and starting this article, I saw several exterminator trucks in Topanga, one going up into the area the bobcat probably lived.
Please do not use rat poison. As we poison the rats, we are poisoning our world and killing one of our more amazing animals.

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