Biologist Karen Krebbs used to study bats in Organ Pipe Cactus National Monument on the Arizona-Mexico border. Then, she got tired of dodging drug smugglers all night.
"I use night-vision goggles, and you could see them very clearly" — caravans of men with guns and huge backpacks full of drugs, trudging through the desert, Krebbs said. After her 10th or 11th time hiding in bushes and behind rocks, she abandoned her research.
"I'm just not willing to risk my neck anymore," she said.
Across the southwestern U.S. border and in northern Mexico, scientists such as Krebbs say their work is increasingly threatened by smugglers as tighter border security pushes trafficking into the most remote areas where botanists, zoologists and geologists do their research.
"In the last year, it's gotten much worse," said Jack Childs, who uses infrared cameras to study endangered jaguars in eastern Arizona. He loses one or two of the cameras every month to smugglers.
Scientists, especially those working on the Mexican side of the border, have long shared the wilderness with marijuana growers and immigrants trying to enter the United States illegally. But tension is rising because of crackdowns on smugglers by the Mexican military, increased vigilance in the Caribbean Sea, new border fences, air patrols, a buildup of U.S. Border Patrol agents and a turf war between cartels.
Smugglers are increasingly jealous of their smuggling routes and less tolerant of scientists poking around, researchers say.
Organ Pipe Cactus National Monument stopped granting most new research permits in January because of increasing smuggling activity. Scientists must sign a statement acknowledging that the National Park Service cannot guarantee their safety from "potentially dangerous persons entering the park from Mexico."
"It's a kind of arms race, and biologists are stuck in the middle," said Jim Malusa, who specializes in mapping desert vegetation. "There's been a chilling effect on researchers."
Scientists say things have gotten more uncomfortable since 2001, when the United States began fortifying its border after the Sept. 11 terrorist attacks. In 2006, the Border Patrol embarked on a hiring spree, with plans to raise its personnel from 12,000 to 18,000 by the end of 2008.
Smugglers have responded with violence. Assaults on Border Patrol agents are occurring at a record pace, with 250 attacks reported from Oct. 1 to Dec. 16, an increase of 38 percent over 2006.
As crossing the border gets more difficult, the fees that smugglers charge to guide illegal immigrants through the desert has doubled in recent years, to as much as $3,000 per person, migrants say. At the same time, Mexico has been stepping up highway checkpoints and port inspections, forcing drug smugglers into the wilderness and onto remote beaches.
To avoid the checkpoints, Mexican drug cartels are moving their marijuana farms northward, from traditional growing areas in Michoacan, Nayarit and Guerrero states to more remote areas in Sonora and Sinaloa states, according to the U.S. government's 2008 National Drug Threat Assessment.
Marijuana smugglers, whose cargo is smellier and bulkier than cocaine, are increasingly abandoning the urban border ports of Texas and California in favor of the Arizona-Sonora corridor, the U.S. Drug Enforcement Administration says. U.S. authorities seized 616,534 pounds of marijuana in the Tucson Sector alone in 2006, up from 233,807 pounds in 2001.
Smugglers also are increasingly relying on boats moving through the Pacific Ocean, the U.S. Coast Guard said this month. The Coast Guard seized a record 356,000 pounds of cocaine this year, most of it in the Pacific.
Scientists, who once had the ocean and desert all to themselves, say they are increasingly rubbing elbows with bad guys.
"They used to take the easier routes through washes and old river beds, but now, they're moving into the rougher country," said Randy Gimblett, a University of Arizona professor who studies human impacts on ecology. "There's a lot at stake because there's a lot of money tied up in drugs. We're not confronting those folks, but we're seeing more of that activity."
There are no statistics on attacks or threats against scientists, said Mark Frankel, director of the scientific-freedom program at the American Association for the Advancement of Science. But among researchers, drug stories abound.
Michael Wilson, a botanist and director of research at the Drylands Institute in Tucson, said he avoids some parts of Mexico's Sonora state since seeing opium poppies, which are not native to Mexico, and mules carrying loads of marijuana down from the mountains. Opium resin is used to make heroin.
Wilson said he has noticed an increase of marijuana cultivation in recent years and more people watching over the fields. Some of his colleagues now carry guns, he said.
"There are a lot of researchers who have ducked out of doing research in Mexico," Wilson said.
David Yetman, a social scientist and host of the PBS series "The Desert Speaks," said he had to stand in a marijuana field in eastern Sonora to get pictures during the filming of a 2004 segment on rural liquor-making. He hired off-duty policemen with automatic weapons to protect his film crew during a piece in southern Sonora, an area known for drug trafficking.
Richard Felger, another botanist, said he stays away from remote mountains in Sonora since being robbed and threatened on research trips.
"I got kind of allergic to pistols being held to my forehead," Felger said.
Gimblett, who relies on buried pressure sensors for his research on park users, said smugglers routinely cut his cables. Childs has tried leaving notes and pictures of saints — even Jesus Malverde, the unofficial saint of drug traffickers — to try to persuade smugglers to spare his jaguar cameras, but to no avail.
Huge swaths of northeastern Mexico are now off-limits to science, said Andres Burquez, a professor at the National Autonomous University of Mexico.
"(Residents) will say 'You can go to A, B and C place, but not D,"' Burquez said. "And it turns out that's the place that interests you most."