As the fence on the Arizona-Mexico border comes into view, Curtis Heim jumps out of an SUV to follow some footprints into a mesquite tree grove.
Weaving among squat cactus and desert scrub, he pulls down a thorny branch. Dangling from it is a nearly invisible fiber from a sugar sack a favorite receptacle of drug smugglers, who cut shoulder straps in the bags and turn them into backpacks.
"No matter how careful they are, there's always something left behind," he says, examining the fiber.
Mr. Heim is a member of the Shadow Wolves, a US Customs patrol that's all native American and that's gained a reputation as having the finest trackers in the nation.
The patrol, which Congress created in the early 1970s, uses traditional native American tracking skills as it takes a frontline position in the war on drugs. Although the Wolves number only 21, they are responsible for about 70 percent of the 40,000 to 60,000 pounds of drugs seized each year by this Customs section an area that includes more than 60 miles of Arizona-Mexico border, as well as the Tohono O'odham Reservation, birthplace of many of the Wolves.
Their skills are so valued that they've been dispatched to several former Soviet states and the Baltics, where they train officers to track weapons smugglers. But they don't need to go halfway around the world to help change the way things work. On the Tohono O'odham Reservation, they've forged links of trust with their fellow native Americans, making some more likely to share information than they would be with Anglo officers.
"It's easier for the local community to share information with someone they know and have a trusting relationship with," says Lawrence Seligman, chief of the Tohono O'odham Police Department. "The reality is, it's always positive to have local members of the community regardless of the culture be a part of the group that's involved in law enforcement."
The Shadow Wolves adopted their name to describe their relentless, round-the-clock pursuit of smugglers. The patrol includes members from a number of tribes, including Navajo, Chicasaw, Sioux, and Lakota, as well as O'odham.
Marvin Eleando, a 26-year Shadow Wolves veteran, is an O'odham born and raised on this reservation. "Growing up, we learned how to track, what to look for when we'd go hunting," he says. His grandfather would wake him before sunrise, and "teach me how to listen, to hear things out in the desert."
The Shadow Wolves augment such traditional skills with state-of-the-art equipment, from ATVs and night scopes to global positioning devices.
Combining the Wolves' home-grown talent with high technology is very effective, says René Andreu, an Anglo, and resident agent in charge for the Customs office in Sells, a scruffy town that's also home to the O'odham tribal government. This mix "is one of the reasons they do so well."
Still, when the Wolves catch their prey, things can get dicey. Heim a Sacafox from Iowa recently sustained bruises when a Ford Excursion struck him during a major drug bust not far from here.
Indeed, a gray feather on the patrol's distinctive shoulder patches symbolizes the death of Shadow Wolf Glenn Miles, who was killed in a shootout with smugglers in 1985. The patch has "become a morale booster, and created a stronger bond between all of us," says its designer, Bryan Nez, a Navajo tracker.
Mr. Seligman notes that bonds have also been strengthened between his police department and the Wolves. "This is a fairly isolated and becoming much more dangerous arena to be a cop," he says. "That's what brings us together."
Those ties are undoubtedly an advantage as both groups deal with the community. Stricken by poverty, the O'odham themselves sometimes turn to smuggling. When those suspects are brought in, "I can usually tell you what family and what village they belong to," says Mr. Eleando.
But working for the federal government isn't always viewed favorably by some tribal members, who still nurse resentment for years of repression.
Ed Cline, an Omaha Indian from Nebraska and Heim's partner, has seen that more than a few times. "A lot of people in our own tribes do resent it," he says. "But I tell them, we're doing what we do for everybody's kids."
Cline is in the driver's seat of the SUV, raising a thick cloud of tawny dust as he slides into gear. But he shudders to a stop when Heim spots another flurry of tracks crossing the hard, rocky flats.
Reading the ground, Heim quickly realizes that these prints are left by illegal immigrants, not by drug smugglers. "You can tell the ones that belong to the drug smugglers they're deeper" because they're carrying a load, he says. Smugglers often try to hide their tracks by strapping pieces of carpet to their shoes, or brushing away footprints.
This inch-by-inch work of the Shadow Wolves may very well be carried on by some of the youths on Tohono O'odham Reservation, who have learned about the top-notch unit at school presentations.
"The kids were impressed that they went to Russia and South America," says Sandy Gutierrez, a career counselor at Baboquivari High School on the reservation. "It's important for the children to know that there are careers that will allow them to come back to the reservation, to work with their people, and to help them."