The vehicle Emil McCain is driving sounds like a golf cart, but this is no golf course. The windowless machine's oversized tires churn through the Arizona outback, lurching over melon-sized rocks. On a steep incline, it seems as if the contraption - a modified all-terrain vehicle - might flip backwards onto itself. For McCain, it's just another Sunday drive.

On this relatively cool July day, he's en route to check one of his jaguar traps. He doesn't expect to find a live jaguar. His traps consist of infrared cameras that are sensitive to heat in motion.

 McCain is a biologist for the Borderlands Jaguar Detection Project, which has rigged more than 40 cameras in the rugged terrain north of the U.S.-Mexico border. Much of McCain's time is spent making the rounds, a good deal of them on foot, recovering images from the cameras. In its six years of operation, the project has amassed in excess of 17,000 images of 25 different native species.

 Among them are some 75 images of jaguars, an endangered species once thought to have been wiped out inside the United States. That thinking changed in 1996, when mountain lion hunters photographed two male jaguars about 100 miles apart. One was sighted in the Baboquivari Mountains southwest of Tucson; the other in the Peloncillo Mountains, which straddle the Arizona-New Mexico border.

 One of those hunters was Jack Childs, a retired land surveyor who described his encounter with a treed male jaguar in broad daylight as "life-changing." Childs and his wife, Anna Mary, founded the borderlands jaguar project in 2001. McCain signed on in 2004.

 With the aid of a couple of volunteers, the Childses and McCain essentially comprise the jaguar detection effort. When they aren't crisscrossing this craggy expanse of the Coronado National Forest, they write research papers, give lectures and craft grant proposals. The quest for funding to keep their project alive is unending.

 Nearly all the jaguar images the project's cameras have recorded feature one specimen. He's known as Macho B, a 125- to 150-pound felid that has prowled these parts for more than a decade. He's been photographed 63 times over a range that exceeds 500 square miles, and he's triggered cameras 12 miles apart within a span of hours. In addition to the still images, the project's remote video cameras have recorded Macho B four times, including once when he was observed marking his territory by spraying his urine. McCain says the scent-marking is significant, because studies of other large felids suggest it signifies residency.

 When Macho B began to regularly trip the remote cameras, Childs and McCain noticed a unique spot on his right side. Jaguars' spots are called rosettes, and researchers use them to identify individuals. The rosette in question bore a distinct resemblance to a caricature of Pinocchio. They compared it to photos Childs had snapped of the jaguar his hounds had treed in 1996. The signature Pinocchio rosette confirmed it was the same animal.

 The project has images of a second male, Macho A, but he hasn't been photographed in three years. Macho A disappeared shortly after images of both cats turned up four hours apart on the same camera. Macho B, apparently, was right on Macho A's trail. Macho B is believed to be 13 or 14 years old, perhaps twice the age of Macho A. McCain thinks Macho B's territorial instincts led him to either kill his younger rival or chase him out of the study area. But Macho B has more to worry about, nowadays, than an interloping upstart. He has to deal with the Department of Homeland Security. Expanded barriers and fencing - under construction and planned on the international border - threaten to sever jaguar migration routes.

McCain parks his ATV and trudges down a trickling watercourse. His eyes are cast perpetually down, scouring the earth for a telltale jaguar sign. He's established himself among the carnivore cognoscenti as a gifted tracker. The crumbling adobe that serves as his field quarters, in fact, contains a clutter of plaster molds and transparencies of predator tracks, and he knows well the subtle differences between the tracks left by a jaguar and those of its much more common cousin, the puma.

 His fascination with nature began as he grew up in the small town of Gardner, Colo., where his father, Jim, is a wildlife sculptor. McCain considers his father to be as much a naturalist as an artist and says the tutelage he received informed a childhood of environmental examination, with a focus on fauna.

These days, the soft-spoken, 28-year-old McCain has particular affinities for elk steak grilled over mesquite, broad-brimmed hats and, especially, predators. He's into falconry (his bird is currently with a friend in Washington state). The Colorado College grad once spent a winter on snowshoes tracking wolves in the Upper Peninsula of Michigan. His study of jaguars has taken him to Costa Rica and Sonora, Mexico. He'd nearly completed his master's degree in wildlife management from Humboldt State University when he met Jack Childs. McCain's become so immersed in the quest to document jaguars that his thesis (on the relationship between pumas and their prey) remains incomplete. He's brought a contemporary ethic to BJDP, an academic yin to the yang of Childs, a drawling autodidact whose grasp of large cats has created a demand for his expertise as far away as Brazil.

 Along the stream, the juniper and scrub oak that dominate the exposed slopes are joined by Arizona ash, walnut, sycamore, thickets of wild grape. A plump Montezuma quail flits into view and vanishes into the brush. Intermittent pools of water, vestiges of yesterday's thunderstorm, teem with thousands of freshly laid frog eggs. They look like tiny crystal pearls.

 The streambed descends gently into a serpentine canyon, perhaps 75 yards from rim to rim and stretching at least as high. The sheer walls of volcanic rock are crowned with pustules and undulating spires - misplaced stalagmites.

 McCain's camera is mounted on a tree trunk under a thick canopy. It's aimed at a bench of flat ground that spreads away from the watercourse.

 "There's a lot of things you look at when you set up a camera," he explains. "Previous signs of jaguars. Other carnivores using the area. Visibility. A lot of it is the landscape, being able to predict how a carnivore is going to travel through. We've gotten quite good at predicting."

 This particular camera - a model marketed to help deer hunters scout for trophy bucks - is digital. He opens the camera case, removes the memory card and loads it into a handheld digital camera. He scrolls through the images and names the subjects that tripped the shutter: Coati, whitetail deer, mice, javelina, mountain lion.

 "It's unbelievable how much stuff is out here," McCain says. "It's a diverse and healthy ecosystem.

 "But no jaguar this time."

 Macho B, in fact, hasn't tripped any cameras since July 17. McCain says Macho B's routine changed early this year after the Department of Homeland Security, in a bid to reduce illegal immigration and drug-running, put up a lattice of retired railroad tracks to serve as vehicle barriers. The welded iron crosses were erected precisely where McCain had tracked Macho B crossing the border.

 McCain replaces the camera battery and snaps the case closed. He gets down on all fours and crawls into the camera's field. A red light blinks, indicating that the infrared sensor is working. Satisfied that the trap is properly set, McCain is ready to move on.

 First, however, he pauses near a bathtub-sized depression in the canyon wall. The alcove betrays the presence of other inhabitants of this country. Migrants have created a shrine, an ersatz diorama complete with a crucifix, a carved wooden bull, a deer antler and a colorful ceramic automobile. There's also a smooth river rock onto which someone has traced a big cat paw with a Sharpie.

 "Obviously left for the crazy jaguar guy," McCain says, chuckling.