Super-toxic rat poisons mysteriously seep into our world

By December 12, 2010October 31st, 20182 Comments

Part 1 of 2

VANCOUVER, British Columbia – With the spooky glow of his headlamp illuminating an antenna in his hand, Paul Levesque stalks one of Canada’s last remaining barn owls.

“Are you getting anything?” research team leader Sofi Hindmarch asks over a walkie-talkie.

“I got it!” Levesque responds. Then a few seconds later, dejected, he radios back: “No. I lost the signal.”

Working in darkness, with the quarter-moon obscured by clouds, these two scientists are trying to figure out what an elusive, radio-collared owl is eating along this country road just beyond the suburbs that ring Vancouver. Their mission is to determine whether the decline of Canada’s barn owl is tied, in part, to super-toxic rat poisons.

Scientists know that at least some owls are dying under gruesome circumstances, bleeding to death from stomach hemorrhages in an agonizing and days-long decline. The culprit: An extra-potent class of rat poisons that has flooded the market in recent decades, designed to more effectively kill rats, a food source for the owls.

Scientist Paul Levesque tries to locate a radio-collared barn owl.
Photo by Paul Joseph Brown, www.ecosystemphoto.com

Six of 164 dead barn owls, barred owls and great horned owls in a 2009 western Canada study had rodenticide levels high enough to kill them outright, causing the fatal stomach hemorrhages. Pesticide readings in 15 percent to 30 percent of the others appeared toxic and seem likely to handicap owls in a variety of ways, scientists say.

The 2009 study is the latest evidence amassed by researchers that poses an unsettling question: Are we willing to poison owls and a variety of other wild animals in order to fight rats?

“We’re finding this stuff all over the place,” said John Elliott, an Environment Canada scientist who co-authored the owl study published last year. “There’s a lot more rodenticide in the food chain than we would have ever thought. We’re surprised that there’s that much of the stuff kicking around.”

Studies in Canada, the United States and Europe show that this newer generation of rat poisons is killing a variety of wild animals, including mountain lions, bobcats, coyotes, foxes, skunks, deer, squirrels, possums and raccoons, along with bald eagles, golden eagles, owls, hawks and vultures.

Hundreds of wildlife poisoning deaths have been documented. In the United States, the pesticides have been found in hundreds of animals, according to a 2006 memo by U.S. Environmental Protection Agency biologist Bill Erickson. Two years earlier, he documented more than 300 incidents of wild animals suspected to have been killed by the chemicals.

“Clearly, more information is urgently needed on the potential impacts such exposure may be having on populations” of raptors and other wild animals, Erickson wrote.

Erickson’s memo was part of a years-long process at EPA that resulted in 2008 in new rules to better control the rat poisons. In June of 2011 those rules go into effect, although they did not go as far as desired by some wildlife advocates, including the U.S. Fish and Wildlife Service.

Researcher Sofi Hindmarch of Simon Fraser University is working to understand the decline of barn owls in British Columbia. Here she bands a baby owl in a barn on the outskirts of Vancouver.
Photo by Paul Joseph Brown, www.ecosystemphoto.com

The chemicals in question are known as anti-coagulants because they prevent an animal’s blood from clotting, or coagulating. The first of these, synthesized in the 1940s, is known as warfarin – the same chemical sold in miniscule concentrations to people as Coumadin, a prescription blood thinner.

The new strain of rat poisons came along in the 1970s. The reason: Warfarin and its cousins required the rats to return to feed on the pesticide over the course of several days. With the newer versions, only a single dose is needed, although it might take five days or more to do the job. Brand names include Havoc, Talon, Contrac, Maki, Ratimus and d-CON Mouse Pruf II.

Some animals are ingesting the pesticides by eating poisoned rats as the rats stagger about, dazed but not yet dead. This goes on for days before the rats succumb, in the meantime making them easy targets for owls and other predators.

But there’s a mysterious wrinkle in this picture. How are plant eaters like deer and sheep ingesting rat poison? Grain eaters like squirrels? What about hawks that subsist almost exclusively on songbirds – songbirds that probably aren’t eating rats?

Scientists wonder: Just how far into the food web have these poisons penetrated?

Canada’s vanishing barn owls

On a balmy but cloudy night, Hindmarch is trying to capture a barn owl, one of three owl species that ingested the rat poisons in the 2009 study. The hunt this night is in a gritty industrial outpost in Vancouver, where rats scamper boldly between the defunct lumber yard where they live and the bustling grain terminal where they sneak their dinner. The barn owls in and around Vancouver are among the last remaining barn owls in Canada. Two weeks ago, they were declared a “threatened” species by the Committee on the Status of Endangered Wildlife in Canada. A smaller population, classified as “endangered,” lives in eastern Canada.

Between the wail of trains on tracks perhaps 30 yards away, Hindmarch and Levesque fiddle with their owl traps, preparing for their 9-5 shift – 9 p.m. until 5 a.m., that is.

“Can you grab one of the girls?” Hindmarch asks Levesque, referring to the mice that they hope will lure an owl to their traps.

The scientists have to carefully put the mice inside cages that will protect the mice when an owl swoops down, attracted by the rodents noisily munching on the crackers that Hindmarch is unwrapping. Hindmarch, of Simon Fraser University, doesn’t want the mice to be hurt.

“It’s working time,” Hindmarch says as she grabs the first mouse in its transport cage and scoots it through the open door of a small cage that’s part of the owl trap. “You’ll get crackers soon.”

Levesque, a freelance contract scientist, takes the cage and searches for just the right spot to put it down in tall grass beside a nearby drainage ditch. He slips in some crackers and steals back to wait inside his truck. Under the tall grass, the noisy snacking attracts barn owls, which are then caught in the trap.

Levesque places a mouse in the trap.
Photo by Paul Joseph Brown, www.ecosystemphoto.com.

Hindmarch’s objective is twofold: to collect the owls’ blood so it can be tested for rat poisons; and to fit the owls with a radio transmitter so she can track them and figure out where they are feeding. She wants to know whether urban owls are eating more poisoned rats than their country cousins.

“This our first time trying to get this guy,” Hindmarch says as she surveys the decrepit lumber yard. “I’d love to get this owl because it’s so urbanized that it’d be neat to see where he’s going and even if he has a nest or has a mate. We have no idea at this point.”

Her work is a follow up to the study analyzing owls found dead in British Columbia and the Yukon Territory, which showed that nearly three-quarters of the birds had rodenticides in their livers. The Canadian findings follow earlier studies in Europe, New Zealand, New York and elsewhere that documented the poisons spreading to wild animals.

The barn owls in and around Vancouver make up the last remaining population of barn owls in western Canada. Although plenty remain alive in the United States, Hindmarch and her colleagues are eager to find out what role rat poisons may be having in the Canadian owls’ decline. The findings will have implications in the United States too.

Taken together, the research suggests that these improved rat-killers are imposing a toxic load on the environment that no one bargained for. It seems clear that some rats are being eaten by owls and other wild animals after they have ingested extraordinarily high doses of poison, researchers say.

“The rats are really little toxic packages running around before they die,” said Michael Fry, a wildlife toxicologist and pesticides expert with the American Bird Conservancy. “If the rat is carrying 10 or 15 times a lethal dose, the animal that consumes it is at a much higher risk of consuming a lethal dose.”

In some cases, the dose isn’t lethal, but “maybe it’s affecting their flying ability and they’re getting hit more by cars,” said Kirstin Webster, a colleague of Hindmarch’s at Simon Fraser University in Vancouver, citing a fairly common way for owls to die.

Owls that aren’t killed outright by the poisons also can easily bleed to death because their blood fails to clot. Wild animals get hurt on a regular basis, scientists say; what otherwise would have been just a painful cut could spell death.

Webster’s work to find a way to test birds’ blood for exposure to rat poisons involved dosing quail with a second-generation rodenticide called brodifacoum.  Some of the quail given the highest doses bled internally, mostly in the abdomen but also in other places where blood can pool. [Editor’s Note: Correction added 12/16/2010 to remove that owls were dosed and that blood came from eyes.]

 Hindmarch checks on baby barn owls in a nest specially built by municipal officials to help preserve the dwindling population around Vancouver, B.C., which was recently labeled “threatened” under the Species At Risk Act. Photo by Paul Joseph Brown, www.ecosystemphoto.com

Once an owl or other animal eats a poisoned rat, the pesticides stay around in the predator’s system for a very long time. It takes six months or longer for just half the dose to be eliminated from some animals’ bodies.

Imagine you’re a barn owl like the one Hindmarch is trying to catch by the grain depot.

“If you’re just getting one dose on top of another, you get this constant exposure,” said Nancy Golden, a U.S. Fish and Wildlife Service toxicologist. “It’s one thing to have enough to kill you outright.

“But what about the ones that are just carrying this body burden? What effect does that have on their fitness? That’s what worries me.”

These “sublethal” effects are difficult to gauge, but research suggests they are real. For example, a study at McGill University in Montreal allowed a sparrow to perch on a pesticide-laden surface. The bird absorbed pesticide through its feet. Then researchers put the sparrow into a big cage along with three undosed sparrows and a kestrel, a small type of falcon that eats sparrows.

Although the scientists could not see any differences in the behavior of the pesticide-dosed sparrows, the kestrel apparently could. In 12 of the 15 instances in which the kestrel preyed on one of the sparrows, it picked the one that had absorbed the pesticide. (That study did not involve rat poisons but it shows that animals not visibly affected may be extremely vulnerable, Environment Canada’s Elliott said.)

The toll of six owls killed outright by rat poisons in the Canadian study almost certainly underestimates the actual rate at which owls are dying from rat poison, Elliott said. Animals that feel sick are likely to secret themselves away to protect themselves against predators.

The birds’ bodies are routinely scavenged by other wild animals, further spreading the poison into the food chain. The chemicals have the “potential to cause additional mortality that may not be sustainable in populations already experiencing critical limitations,” biologists from the United Kingdom’s University of Leicester reported in 2005.

California’s threatened San Joaquin kit fox is an example. Scientists collected carcasses of the big-eared, long-legged fox that died from various causes in Bakersfield and in an area 30 miles out in the country. Nearly all the dead foxes from Bakersfield had residues of the long-lived second-generation rodenticides, while none from the outlying desert did.

How are these rat poisons getting into plant eaters low on the food chain? There is no sure answer for now. Scientists wonder, though, if carcasses of poisoned animals are being scavenged by creatures low on the food chain. Or perhaps insects are crawling inside the bait stations. But there could be other ways, too. Elliott, the Environment Canada researcher, notes that scientists have seen voles and birds hopping inside the holes on the side of bait stations that approximate the size of the openings to their burrows or homes inside trees.

And as for deer? The seven that tested positive for rat poison in New York “apparently were exposed due to misuse and careless bait application,” Erickson of the EPA reported. Elliott noted that big blue blocks of the poisoned bait are sometimes thrown out into the wild – blue blocks that look a whole lot like the salt licks that deer are known to frequent.

Cracking down on rat poisons

Pushed by environmentalists who successfully sued in federal court, the EPA in 2008 issued rules for these rat poisons that largely take them out of the consumer market.

Pesticide manufacturers say EPA’s action was overkill, but should eliminate any doubts about the products’ safety for wildlife.

“There was not strong evidence to compel (EPA) to put into place the (new rules). However, they did so,” said Karen Reardon, director of communications at Responsible Industry for a Sound Environment, which represents pesticide manufacturers. “We have now even further added protections for secondary wildlife exposure.”

Dale Kemery, an EPA spokesman, said the agency does not track the amount of pesticides manufactured or applied. But New York state does tote up the applications. New York State Department of Conservation records requested by the Natural Resources Defense Council for use in a lawsuit to limit the rodenticides’ use showed more than 20 tons a year were applied in eight New York City Zip codes in 2002. The pesticide manufacturer Syngenta International in 2004 revealed that some 10 million pounds of first- and second-generation rat poisons were sold annually in California. And in British Columbia, scientists obtained records showing large increases in their use during the 1990s.

The western Canadian study documented a 100 percent increase in sales of one of the rat poisons, brodifacoum, and a 24 percent increase in another, bromadiolone, in British Columbia between 1991 and 2003.

Canada in 2006 changed the rodenticides’ labels to require that they be used in dog- and child-proof bait stations that allow only rats access to the poison, or that the bait be limited to where kids and animals don’t have access.

Then, in 2009, six months before release of the study of the owl poisonings, Health Canada issued stricter regulations. Their inspiration came from a contentious rule approved south of the border.

In the United States, the EPA knew by the early 1980s that the pesticides that emerged the decade before were affecting non-targeted wildlife. But it was 1999 before the agency’s scientists launched a comprehensive risk analysis of the pesticides’ effects on wildlife.

George W. Bush was president by the time an EPA document outlining the environmental risks of the rat poisons was ready to go out for public comment. EPA sent a draft of the document to the pesticide industry in September 2001 for what was supposed to be a 30-day technical review. The stated purpose was to allow industry officials to make technical corrections.

Instead, the agency held a series of closed-door meetings with industry officials, environmentalists charged. “There has been excessive undue influence from industry on the entire process,” said the group Beyond Pesticides. “There has been little to no opportunity for any other stakeholder to provide input or even attend any of these meetings with EPA.”

Levesque assembles an owl trap.
Photo by Paul Joseph Brown, www.ecosystemphoto.com

Reardon of the pesticide industry group said it’s clear the pesticide industry didn’t get special treatment from EPA because the industry opposed what the agency ended up requiring. “EPA has added additional safeguards on top of what was already required. One must conclude that EPA’s actions satisfied what they believed was additional risk,” she said.

In January of 2003, the agency released preliminary results for public comment. This came more than three years after the risk analysis began. It took EPA five more years, until May of 2008, to complete a regulatory review.

And then, a quarter-century after the poisoning of wildlife became well known, the agency decreed that rules to protect wildlife would go into effect more than three years later, in June 2011.

Under the new rules, use of the second-generation rat poisons by consumers will be curtailed. The sale of loose rat baits will be banned in “big box” stores like Home Depot as well as other retail outlets. However, consumers can purchase up to one pound of bait in bait “stations” that are designed to keep out kids and dogs.

Professional exterminators as well as employees of farms, warehouses and other commercial installations may continue to use the more-toxic rat poisons, and loose baits. However, they are required to use above-ground bait stations if the bait is left outdoors or in any place accessible to children, pets or wildlife.

The rules represent a significant check on unsafe use of the products by consumers, said Rick Keigwin, director of EPA’s Pesticide Re-evaluation Division “We wanted people who are professionals in the field, who have the training, to use these products in the appropriate way,” he said.

The U.S. Fish and Wildlife Service and others pushed for EPA to disallow all outdoor uses of the rodenticides, with narrow exceptions.

EPA didn’t go that far, said Laura Parsons, an EPA biologist specializing in pesticides, because of pushback from some businesses. For example, she said, “restaurants and food-service facilities felt very strongly that they needed some kind of perimeter control.” The EPA’s position was backed by the U.S. Department of Housing and Urban Development and the federal Centers for Disease Control and Prevention.

Professional pesticide applicators support the new “common-sense” rules, said Bob Rosenberg, vice president of the National Pest Management Association, and opposed efforts to ban outdoor use of the more-toxic products.

“Rodents are serious problem for all the reasons you know about – public health reasons,” Rosenberg said. “It’s a lot better to get them outside rather than inside the structure. You want to get them before they get to the food.”

Meanwhile, the multinational Reckitt Benckiser, which markets d-CON rat baits, is challenging the EPA’s new rules in court in an effort to prevent them from going into effect.

The least-toxic answer, said Golden, the Fish and Wildlife Service toxicologist, is a system known as “integrated pest management.” It emphasizes use of non-toxic pest-control methods, which in the case of rats translates to trapping the rats inside the house and finding ways to keep any more from getting in.

Golden predicted that poisoning of wild animals will continue.

“I wouldn’t use anticoagulants in my back yard,” said Golden. “These things are pervasive and are turning up in places we did not expect. . . . They’re certainly not contained where we think they are.”

This story by InvestigateWest was commissioned by Environmental Health News, a non-profit journalism site that seeks advance the public’s understanding of environmental health issues.

Robert McClure

Robert McClure

Robert is co-founder and executive editor of InvestigateWest. At the Seattle Post-Intelligencer, Robert exposed a major weakness in the Endangered Species Act and deficiencies in Puget Sound restoration efforts. His reporting on hard-rock mining won the John B. Oakes Award for Distinguished Environmental Journalism. A Pulitzer Prize finalist, Robert is a longtime former board member of the Society of Environmental Journalists; he currently serves as chair of the editorial board of SEJournal. Seattle Magazine in 2013 chose him as one of Seattle's "most influential" people.


  • Sadie Anderson says:

    Thank you for this wonderful article. Please add any info that may help the public take action to get these rodenticides locked up better. Also adding any information to help protect owls would be great. I know they are also being harmed by higher and higher amounts of light pollution here in our beautiful Northwest.

  • Debra Burnett says:

    I rescue Barn Owls. They nest in haystacks here in the Columbia Basin of Central Washington and around March when the weather breaks, the haystacks get sold and last year I raised 30-hatched one myself! But the reason I am writing is because I am located in Manson, WA on Lake Chelan. Wineries are popping up all over the place, replacing the apple industry. In California a wine maker uses Barn Owls for rodent control. (Google tommy51). My goal was to get growers interested, throw some boxes up-maybe throw a video feed so people could watch (see Molly the barn owl) anyway, I got on the radio with all the Barn Owl’s statistics-the # of rodents they consume, don’t eat cat’s, they are found globally which gives us the opportunity to exchange information with other areas of the world. I was on that radio begging for mice money. At times in a young owls life they may eat as many as 8 mice a day. Do the math. Bottom line: These creatures are perhaps one of the if not THE most valuable on this planet simply because to the food it eats. And we ….no not me. THEY are poisoning them. I have a video of one of the owlets taking it’s last breath, dying from a poisoned mouse someone caught in a trap and saved for me. The moment I smelled the owlets’ breath I recognized it. I no longer accept any wild mice. I also know first hand, it doesn’t take long before a new generation of mouse comes along that is immune to the poison. I’ve seen it when I lived in Seattle.
    Everyone talks about going green. Growers claim bragging rights because they are certified organic. pfffft “Synthetic Organic Rodenticide” is the oxymoron that I keep hearing…really? .
    And now the wineries are adding “Water Features” to their properties, complete with koi. Well guess what? THere are more animals around here that will eat them than those that won’t. And they will keep coming back until every one is gone. I’m guessing the illegals will shoot whatever is bothering the “water feature” under the cover of darkness .They’ll do anything they are told.
    Im done.
    I just want to market the Barn Owl…in a good way. I need help. I can’t afford to continue and can’t bear knowing many will die without me.

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