Bobcats face deadly diseases, weakened immune systems from exposure to household rat poison
New study in Whittier-Puente Hills looks at mange deaths of healthy wildcats
Caught between the green lawns and the brown hills of Southern California is the North American bobcat, Lynx rufus.While not technically endangered, scientists as recently as June have watched healthy bobcats die of severe mange, a common skin disease caused by parasitic mites normally afflicting canines. Local scientists believe the tuft-eared wildcats are being poisoned by eating gophers or ground squirrels that have ingested rat poison left in yards by homeowners or near dams and other government structures. The rodenticide, an anticoagulant, enters the bobcat's digestive system as a prolonged secondary exposure, making them unable to fight off common diseases such as mange.
"We feel, what might be going on, which at this point is still a theory, is the rodenticide is compromising their immune system in some way and that is may be associated with them getting mange disease," explained Joanne Moriarty, research ecologist with the U.S. National Park Service in Thousand Oaks who has been studying bobcats there since 2004. Moriarty is the first scientist to connect dead bobcats to prey that ingested rat poison. "We saw a statistical correlation between the anticoagulant (rat poisons) and mange disease," she said Tuesday.
Indeed, necropsies done on bobcats since the NPS study began in 1996 produced this astounding statistic: 92 percent of the dead bobcats analyzed tested positive for rodenticides, she reported. "Some are trace, but some are high levels," she said. This deadly connection at first was confined to the Simi Hills, Thousand Oaks, Agoura Hills and Oak Park, where the collared bobcat population dropped by 50 percent from 2003 to 2006. Since then, mange has overtaken vehicle collisions as the No. 1 cause of death for bobcats in Southern California, the NPS reported.
A familiar pattern
Ecologists discovered a similar connection between bobcats and severe mange just last month in eastern Los Angeles County, giving credence to Moriarty's theory and casting a shadow over bobcats' survival in the urban interface. In January, local scientists with the U.S. Geological Survey collared two bobcats as part of a $469,000 study started last fall in the Whittier-Puente Hills. After watching the healthy couple for months, suddenly the female cat, WIN, died of severe mange and her partner, ZEK, a male, a short time later also contracted severe mange and nearly died.USGS ecologists acted quickly by re-capturing ZEK a few weeks ago and speeding him to treatment. Today, he's recuperating at an Orange County veterinarian clinic -- its exact location is a secret.
biologists studying Bobcat travel routes through highway culverts
Will ZEK survive? "Possibly," said Erin Boydston, USGS research ecologist working on the Whittier-Puente Hills bobcat study. "He is eating. But we don't have the full picture on his health status," she said Tuesday, while downloading memory cards from remote cameras her team has placed on Powder Canyon Trail in Rowland Heights. "It is still a little early to know his longer-term prognosis," she added by email Friday.
When her team monitoring the collared bobcats noticed a healthy ZEK had begun to look sickly, they remotely released his transmitting collar, re-captured him and brought him to a veterinarian. "His health has been compromised. The only thing we can see outwardly is he has patterns fitting mange and the debilitation that accompanies the severe mange," Boydston said.
Boydston's team has volumes of data on ZEK, his whereabouts and his contacts with female bobcats that they hope will help the NPS scientists solve the riddle of why bobcats are getting mange and, also, why they can't seem to fight it off. So far, the pattern keeps repeating itself. Boydston also worked between 2007-2010 on a bobcat study near the 71 and 91 freeways in western San Bernardino County, near Los Angeles, Riverside and Orange counties. There her team collared 15 bobcats and 12 coyotes. They also did necropsies on bobcats run over by cars."We collected liver tissue from bobcats found dead in Orange County, and most livers tested positive for one or more anticoagulant compounds. What we found is consistent with what the Park Service has already found and published, that bobcats in general in this region seem widely exposed to anticoagulants," Boydston said.Moriarty said the correlation only exists where humans are close by. "It is always associated with urban areas," she said.
Study being cut short
The Puente Hills Habitat Preservation Authority watches over 3,860 acres of open space from the 605 Freeway to Harbor Boulevard in La Habra Heights, and itself owns about 1,878 acres. It is responsible for contracting with the USGS for the bobcat study, even though it is being paid for by Matrix Oil Corp.
Matrix is partnering with the city of Whittier to drill for oil on a 7-acre portion of the preserve that would affect about 20 acres. However, a court ruled in June that the project cannot go forward because the land was purchased for perpetual open space using Proposition A monies raised by taxpayers throughout Los Angeles County.
As a result of the court ruling and the oil company withholding further payment, the USGS study will be placed on hold around Aug. 1, said Bob Henderson, chairman of the Habitat Authority board and a Whittier City Council member. So far, the company has spent about $300,000 on the study, Henderson estimated.
The court may view the study as benign and allow the USGS to continue. Or, the Habitat Authority is considering hiring the crew back. But whether or not the study resumes, the data collected from 33 remote cameras and the two collared bobcats during the past 11 months will be analyzed by the USGS scientists
.
Ban rat poison?
The fate of the bobcats -- elusive creatures who rarely interact with humans -- may hang in the balance.
"The question is: Are we losing them? And if so, can we do some management type things?," Henderson said. One idea being tested by the city of Malibu is to ban the sale, purchase and use of rodenticides that lead to the deaths of pets and wild animals.
The proposed ordinance, suggested by Council members Lou La Monte and John Sibert, will be discussed by the Malibu City Council on Monday. City Manager Jim Thorsen's report says residents are concerned about the deaths of pets and wild animals such as hawks, owls, foxes and coyotes either from direct exposure or indirect exposure to rodenticides.
If adopted, the city would stop using these products in their parks as well. One alternative is to use traps, according to the city report.Henderson said the Hacienda Golf Club, a private golf course in La Habra Heights near the Whittier wildlife preserve where the bobcats roam, has already agreed to use only physical traps to eradicate gophers.
The killing of wildlife from secondary exposure to rodenticides is similar to the deaths of bald eagles by DDT in the 1960s before it was banned. Since then, the bald eagle population has rebounded.
The California Department of Fish and Wildlife warns particularly against over-the-counter rodenticides such as d-Con containing the active ingredients brodifacoum, bromadiolone or difethialone which are strictly to be used indoors and are illegal to use in open areas or fields. Products containing chlorphacinone and diphacinone are less toxic to mammals and these chemicals are eliminated more quickly from an animals's body, according to the CDFW.
There is some good news.
The bobcat population in the Santa Monica Mountains is beginning a comeback from the mange episodes, Moriarty said. She's extremely interested in what Boydston and the USGS come up with in the eastern part of Los Angeles County."Even though the population is coming back, we don't know if another wave will hit," she said.
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Bobcats by the numbers
72,000
estimate of the number in California
309
bobcats collared by NPS ecologists in Santa Monica Mountains area since 1996
2
bobcats collared by USGS ecologists in Whittier-Puente Hills study
92
percent of bobcat necropsies in which rodenticide was found
33
movement-triggered cameras placed in Whittier-Puente Hills for USGS study
1 million
photos taken by USGS cameras in Whittier-Puente Hills so far
1,300
average range in acres of a typical male bobcat
$469,000
cost of USGS study in the Whittier-Puente Hills
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