WASHINGTON » Anything that hops, burrows, buzzes, crawls or grazes near a nuclear weapons plant might be capable of setting off a Geiger counter. And at the Hanford nuclear reservation, one of the dirtiest of them all, its droppings alone might be enough to trigger alarms.

A government contractor at Hanford, in south-central Washington state, just spent a week mapping radioactive rabbit feces with detectors mounted on a helicopter flying 50 feet over the desert scrub. An onboard computer used GPS technology to record each location so workers could return later to scoop up the droppings for disposal as low-level radioactive waste.

The Hanford site, overseen by the U.S. Department of Energy, produced roughly two-thirds of the plutonium used in the nation's nuclear weapons arsenal, beginning in World War II and ending in the 1980s. Today it is the focus of the nation's largest environmental cleanup, an effort that has cost tens of billions of dollars and is expected to continue for decades.

Yet the helicopter flights, which covered 13.7 square miles and were paid for with $300,000 in federal stimulus money, took place in an area that had never been used by the bomb makers.

The area had, however, been used by rabbits that had also burrowed into other areas that were contaminated. Many of the contaminants were in the form of salts, which attract wildlife. The rabbits carried strontium and cesium, which emit gamma rays, back out of the area in their digestive tracts.

The flights were far less expensive than other strategies, said Dee Millikin, a spokeswoman for the contractor, a subsidiary of the engineering and environmental consulting company CH2M Hill.

Walking through the area with radiation detectors would have taken eight months longer and cost $1 million, she said.

The flights were first reported by The Tri-City Herald newspaper of Kennewick, Wash.

The rabbits themselves are not a target of the operation: The area from which they picked up the contamination was paved over years ago, so the source was sealed off, Millikin said.

Rabbits were not the only biological vectors contaminated by the nuclear residue. Mice and badgers also picked it up, she said, and coyotes feed on the contaminated smaller animals. “;It's basically a circle-of-life situation,”; she said, adding that researchers have also found traces of radioactive materials in fish of the adjacent Columbia River.

Yet roaming rabbits appear to account for the overwhelming bulk of the radioactive excrement located in the flights, Millikin said.

Technicians have monitored rodents and waterfowl at Hanford for radiation since 1947, and have identified about 5,400 incidents of “;biological intrusion.”; It is not only animals; tumbleweeds have roots deep enough to pull up radioactive material and then carry it as they blow away, said John Price, who monitors conditions at Hanford for the Washington state Department of Ecology.

Marylia Kelley, the executive director of a California group called Tri-Valley Communities Against a Radioactive Environment, said the rabbit cleanup was “;kind of funny, in a sick way.”;

Hanford is not the only reactor site that has prompted concern about contamination spreading to animals, Kelley said. For environmentalists focusing on the Lawrence Livermore Nuclear Laboratory in California, for example, she said, the priority is to keep endangered or threatened species like the California tiger salamander and the red-legged frog out of contaminated areas.

At that site, she said, contamination has been somewhat harder to track because it is mostly plutonium, whose main emission is alpha particles that travel only a few inches in air, unlike the gamma rays from cesium and strontium at Hanford.

Radiation is also a concern at the Savannah River nuclear site in South Carolina, where neighbors can enter a lottery every year to be allowed to hunt deer. “;All harvested animals are tagged and brought to our check station, where they are monitored for cesium-137,”; the site's Web site advises.

“;If they find something that was above the limit, they take out that part of the carcass and allow the guy to go on his merry way with the rest of it,”; said Robert Alvarez, an environmental expert and former Energy Department official.

In the 1980s, researchers found turtles contaminated with radioactive materials on a hog farm near the Savannah River plant. The discovery briefly prompted concern that the radioactivity could move into the human food chain, although such a pattern was not detected.

As the federal government pursues cleanups at various nuclear sites, experts have deliberately contaminated a species to further their efforts: honeybees. The Environmental Protection Agency says honeybees have been used to map radioactive materials on five federal nuclear reservations, including Hanford, as well as heavy metal pollutants.

Workers position a hive at a suspect area and wait to see what the bees come back with. Researchers can measure the radioactive content of the bees' honey or wax, but “;the recommended sample is the bee itself,”; the agency said.