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'Super-toxic' Rat Poisons Killing BC's Rare Barn Owls, Other Wildlife

Owls are bleeding to death slowly and agonizingly. The culprit: extra-potent rodenticides poisoning wild animal food chains. Part one of two.

By Robert McClure, 13 Dec 2010, Environmental Health News/InvestigateWest


Simon Fraser University researcher Sofi Hindmarch tagging a young barn owl in the loft of a historic barn in Surrey, B.C. Photo by Paul Joseph Brown,


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.

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 per cent to 30 per cent of the others appeared toxic and seem likely to handicap owls in a variety of ways, scientists say. Barn owls in particular could be hurt -- in Western Canada they no longer live anywhere outside the Lower Mainland, and two weeks ago the Committee on the Status of Endangered Wildlife in Canada recommended upgrading their protections under the Species At Risk Act, reclassifying them as "threatened" instead of merely being a "species of special concern." A smaller and more gravely imperiled population, classified as "endangered," lives in Eastern Canada.*

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?

New rules won't do it: US Fish and Wildlife

"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.

Easy, but deadly, prey

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.

Between the wail of trains on tracks perhaps 30 yards away, Hindmarch and Levesque fiddle with their owl traps, preparing for their 9 to 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.

Hindmarch's objective is twofold: to collect the owl's blood so it can be tested for rat poisons; and to fit the owls with radio transmitters 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 is 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.

'Little toxic packages'

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 brodificoum. Some of the quail given the highest doses bled internally, most commonly in the abdomen but also in other places where blood can pool inside the body.*

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.

Studying effects of 'constant exposure'

SFU researcher Sofi Hindmarch, Owl

Petri dishes with prey remains found in barn owl pellets in Sofi Hindmarch's lab at Simon Fraser University in Burnaby, B.C. Photo by Paul Joseph Brown,

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 un-dosed 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.

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