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.

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 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.

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.

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