美国国家公共电台 NPR Scientists Get Down And Dirty With DNA To Track Wild Pigs（在线收听）

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So biologists have invented a new way to track wild animals. They pick up on traces of their DNA. It's kind of like wildlife CSI. NPR's Rae Ellen Bichell tells us that this is helping some states track down a destructive invader.

RAE ELLEN BICHELL, BYLINE: In the foothills of Colorado's Rocky Mountains, a gravel road leads to a 10-foot-tall metal fence. Type in a key code and one gate scrapes open. Behind that, another. The residents of this facility are wild pigs.

(SOUNDBITE OF PIG GRUNTING)

BICHELL: They're playing in the snow and asking for someone to scratch the bristles on their ridged backs. Biologist Morgan Wehtje studies these pigs, which were raised in captivity and now live at the National Wildlife Research Center in Fort Collins.

MORGAN WEHTJE: These are nice animals. They've been handled since they were piglets.

BICHELL: But make no mistake, these beasts can do real damage. The pig next to Wehtje weighs as much as an NFL tight end.

WEHTJE: Which is why if they were to run at you, they'd take you out.

BICHELL: Out in the wild, their less cuddly counterparts are an invasive species destroying the landscape in much of the U.S. They will eat anything from rows of corn to baby deer and goats. They've also been known to eat human corpses on occasion. In Texas, they're tearing up yards in the suburbs. In Louisiana, they damaged levees by digging for food.

WEHTJE: They just rototill the landscape and consume kind of everything in their path.

BICHELL: Though pigs arrived on this continent 500 years ago with early explorers, for some unknown reason, their populations have really exploded in the last 30 years or so. There are now at least 6 million pigs across the country. And they're hard to get rid of despite the money that state and federal legislators have funneled into controlling these animals. But wild pigs may have met their match - Kelly Williams. She's a genetics researcher with the National Center for Wildlife Research. And she and her colleagues have found the Achilles heel of hogs.

KELLY WILLIAMS: So pigs are attracted to intermittent, stagnant, turbid water bodies.

BICHELL: Also known as mud and dirty water. When pigs drink, roll or wallow in it, they leave bits of themselves behind - drool, hair, skin cells, a wildlife crime scene of sorts. Williams figured out a way to pull the DNA from that evidence sometimes up to a month after a pig has visited a site. All she needs is a scoop of dirty water, like this one from Texas.

WILLIAMS: There's a lot of, like, junk floating around in there. Sometimes they look like chocolate milk, sometimes it looks like lemonade.

BICHELL: She spins down all the solids, isolates the DNA inside and compares it to pig DNA. At the end, she has an answer - yes, pigs were here or, no, they weren't and passes it along to people like Brian Archuleta. He's a wildlife biologist with the U.S. Department of Agriculture in New Mexico. And he has a goal for the New Year - pig annihilation.

BRIAN ARCHULETA: Total elimination by the last day of September of this year.

BICHELL: That is a big goal given the fact that he covers eastern New Mexico, thousands of square miles of desert, mountains and sand dunes right next to Texas, which is teeming with pigs.

ARCHULETA: Eastern side of New Mexico is a big place, lots of country. We are looking for a needle in a haystack.

BICHELL: Recently, he sent a few people to collect water and then shipped it to Kelly Williams. With her results, he was able to narrow the search down to about ten square miles. So Archuleta booked a helicopter, hired some sharpshooters and flew over the areas where pig DNA had been found. They shot eight hogs in one place, 13 in another. That, he says, is progress. Rae Ellen Bichell, NPR News.