The mission of the Agriculture Department's Wildlife Service is to mitigate conflict between humans and wildlife. But critics say some of its activities are cruel to animals and that it should be more transparent.

The USDA's inspector general is conducting an audit of the agency. Results are expected later this year.

Wildlife Services has been around in some form since 1895. In a video on its website, a Wildlife Services biologist demonstrates one of its biggest jobs, chasing birds from airports. In this case the biologist uses pyrotechnics to scare them.

USDA Administrator Kevin Shea says Wildlife Services' mandate is pretty simple.

"Our role is to help when people and wildlife come into conflict," Shea says, "try to mitigate the damage while not endangering any species or the land."

Those conflicts between people and wildlife have become increasingly common. Wildlife Services traps and kills invasive species like nutria, a possum-like rodent that tears up the wetlands around the Chesapeake Bay, and feral pigs, which are rapidly spreading across the U.S.

Out West, Wildlife Services is engaged in its most controversial activities.

"What Wildlife Services does is run around the country killing things like bears and mountain lions and coyotes and wolves and millions and millions of birds and other animals," says Andrew Wetzler, director of wildlife conservation for the Natural Resources Defense Council.

The NRDC, along with other environmental groups, is a fierce critic of Wildlife Services. Wetzler says the agency is essentially an exterminating service for private ranchers, using tax dollars to kill predators.

"We know that they've killed 100,000 native carnivores every year," Wetzler says. "We know that they use poisons, they use aerial gunning from helicopters and airplanes, they use traps and snares, and they even club animals to death in their dens. But we don't know how much they use on each method or where the methods are used."

Another critic of the agency is Oregon Democrat Rep. Peter DeFazio. DeFazio says he's tried to get answers from Wildlife Services officials about their activities, but without much luck.

"It is probably one of the most opaque, unaccountable agencies in the federal government," DeFazio says. "I've served on Homeland Security for a number of years, and I can safely say that the doings of Wildlife Services are much more obscure."

DeFazio says it's unclear how the agency spends its budget of about $87 million. He says ranchers and farmers have a right to kill predators that attack their livestock, but he doesn't think the government should be picking up the tab. He also questions some of the methods Wildlife Services employs, including cyanide and explosive traps.

"They use a shot shell that shoots cyanide after you pull on a bait, and so dogs frequently will pull on the bait and they will die a very horrible death," he says. "Humans have attempted to run over to their dogs and gotten secondary cyanide poisoning. That's happened in my district and elsewhere around the country."

Shea, the USDA administrator, says his agency collects fees from ranchers to pay for its work. He says lethal methods are used sparingly, and as a last resort.

"Sometimes the predators are in remote places where it's best handled through aerial hunting," he says. "Sometimes it's best handled by traps, and sometimes we can use very specific deterrents — for example, a livestock protection collar on sheep. Literally, only the predator who bites on that collar is ever going to be harmed by that poison."

Shea says Wildlife Services is working to become more transparent. He says every lethal encounter is now posted on its website, and he notes the agency's mission has been repeatedly reauthorized and funded by Congress.

A request by Rep. DeFazio and his Republican colleague John Camp of California led to the USDA's audit.

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