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News: 08/15/2018

Fox killed by rat poison demonstrates law of unintended consequences

Three grey foxes
Three grey foxes cavort on Tom Richards’ patio furniture at his house on Warm Springs Road. Photoy by Tom Richards

A few weeks ago, two Warm Springs Road neighbors found a female grey fox dead by Sonoma Creek. Both had seen their longtime wild resident fox stumbling and disoriented in the previous few days. Information from Marin County’s Wildcare suggested the fox was very likely poisoned from ingesting a gopher or rat killed by rodenticides.

“Unfortunately, this type poisoning of our native wildlife (and our domestic pets and even our children) is on the rise due to the use of rodenticide poisons as a way of dealing with a rodent problem,” said Tom Richards, one of the neighbors who found the fox. Richards has been a creekside resident for 15 years.

Richards has gathered a good deal of information on how rat and gopher poisons affect wildlife, and the Marin-based Wildcare website is loaded with information about how to deal with unwanted rodents.

Whatever the steps taken to curb infestations, poisoning is one of the very worst solutions. Richard’s dead fox is a case in point. That fox, in a healthy life, would have destroyed and consumed literally thousands of the pests. Now, the poison used to kill one or two rodents has eliminated one very efficient rat and gopher killer.

The same holds true for owls, dogs, cats, and other natural predators.

Some eye-opening facts were developed through concentrated studies back in 2013 by the Wildcare group.

“Of the 138 samples sent to the California Animal Health and Food Safety Laboratory (CAHFS) at U.C. Davis in 2013, an astonishing 76.8 percent of tested [wildlife] patients show some exposure to these toxic poisons.” The findings referred to rodenticides, a specific class of poisons aimed at mice, rats, gophers, moles and other small pests.

“Foxes are nocturnal – they sleep during the day and hunt at night,” Richards wrote in a communication. “Their primary food source is small rodents such as mice, voles, moles, gophers, and rats, all of which are nocturnal as well. As such, they are far better at rodent control than the domestic cat, which is not nocturnal. In fact, in the UK smart gardeners are encouraged to have a ‘garden fox’ to control these pests. Our neighborhood along Warm Springs Road near the creek had a severe rat problem before the foxes came. Now, no rat problem!”

Richards also researched some of the prevailing myths about foxes.

Foxes don’t attack people or most domesticated animals, though they may turn if cornered or threatened. They do like a chicken now and then. They are rarely rabid — there was not a single reported instance in California of a rabid fox in 2015, according to California’s Department of Public Health (report, Oct. 2016).

The Coumadin-based pill that many people take to prevent blood clots was originally developed as a rat poison, one of a group of poisons called anticoagulants. These poisons keep blood from clotting and eventually cause the animal to bleed to death internally. In the concentrations used for rat poisons, they have come under increasing scrutiny and regulation. One of these anti-coagulants, brodicacoum, a “second-generation” anticoagulant rodenticide (SGAR) was found to have adverse impacts on wildlife.

“Brodifacoum delivers a delayed lethal dose to the target rodent with the first feeding that does not kill the rodent immediately. After multiple feedings a rodent may have a significant ‘body burden’ of this persistent pesticide at death and may lead to non-target wildlife exposures through contact with the dead or dying rodents.” (Department of Pesticide Regulation, CA Notice 2014-09, 2014). These substances can only be sold by licensed dealers and used by certified applicators.

However, the first-generation anticoagulants, acute toxicants, and some fumigating gas used on burrows, mostly developed in the 1940s, are still available to consumers. The California Department of Pesticide Regulation (DPR) is continuing to monitor wildlife deaths and may take more steps if necessary.

A big problem with poison, according to DPR, is that “rodenticides do not eradicate rodents and may not reduce their numbers for long. If there’s an area-wide population, rodents from the edges move into the available space vacated by the poisoned rodents. … The best way to reduce rodent populations is to eliminate factors that allow rodents to reproduce and thrive.” This is quoted from a fact sheet published by the department online.

Rodents are a problem in the city and the country, but can be truly exasperating in country property near water – creeks, ponds, rivers, marshlands – all the features that make Sonoma County and Sonoma Valley a beautiful place to live.

The DPR says the safest and most effective ways to solve rodent problems are through exclusion and sanitation. For example, seal off any rodent entrances to your home, remove debris from your yard, and make pet food inaccessible to rodents. Traps can also help reduce rodent numbers. When you use rodent bait in a bait station, follow label directions carefully and immediately dispose of any rodent carcasses.

Kenwood and Glen Ellen are both in an Endangered Species special zone that applies to anyone with property within 100 feet of a creek – Sonoma Creek for example. The second-generation poisons may not be used by anyone unlicensed, have to be placed in Tier One traps, and placed within 10 feet of the home or building being protected. A Tier One trap keeps the trapped animal inside until it dies.

California law is specific about trapping wildlife: you either let it go or kill it on the spot. You are not allowed to transport the mouse or any other wildlife anywhere else. There’s too great a chance it can take disease and unwanted bacteria, viruses and other contamination with it.

Barn owls are one of the best rodent predators on the planet, along with coyotes and wild cats – bobcats and mountain lions. Yes, the big cats love a tasty mouse when it pops up. Find out how to get a barn owl box at Sonoma County Wildlife Rescue.

If you would like more information, visit Marin Wildcare, the Sonoma Ecology Center, and the Sonoma County Agricultural Commissioner’s webpages.

Meanwhile, think again about setting out poison to kill mice. They may just crawl into a wall space and really stink up the place for months.


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