Scrolling through images of bobcats and deer snapped by the camera, he explains how the habitat for one of the United States' most elusive predators is being pressured by illegal immigration from Mexico and the controversial remedies sought by the US government to curb it: building fences.

In this election year, Washington hopes to complete 670 miles (1,070 kilometres) of pedestrian fencing and vehicle barriers in a bid to seal off some of the most heavily crossed areas of the nearly 2,000-mile (3,200 km) border, despite opposition from some landowners and environmentalists.

"The low flat valleys are effectively walled off to wildlife. As a result everything is funnelled up through the high mountain ranges that span the border" McCain said, standing by the camera box in an area spotted with trash tossed by illegal immigrants.

"The border barriers are directly linked with the funnelling of people into the last remaining habitats. Jaguars are very solitary animals, they can't move freely where there are a lot of people."

SOLITARY HUNTERS

Jaguars are powerful, solitary hunters that were revered by ancient cultures including the Aztecs and the Maya who believed they had supernatural powers. They roam over a vast habitat ranging from northern Argentina in the south to the rugged, borderland wildernesses of Arizona and New Mexico, although they are rarely seen.

The sturdy, spotted cats -- which are the only roaring felines in the Americas -- were believed to have become extinct in the United States until an Arizona rancher photographed one he encountered while hunting mountain lions in the far southwest corner of New Mexico in 1996.

"It was unforgettable, probably the most exciting day I have had in my life," Warner Glenn said of his brush with the burly, roaring male jaguar, which his hounds briefly brought to bay on a pillar of rock in the Peloncillo Mountains.

Proof positive of their presence in the United States was gained six months later when another Arizona cougar hunter, Jack Childs, treed and photographed a second jaguar in the distant reaches of the Baboquivari Mountains southwest of Tucson.

"They were on the brink of extirpation and to find out they were still here was a really great thing," Childs said of the animal, another male, which his hounds chased up into an alligator juniper tree.

"It was indescribable, a life-changing experience. We tipped our hats to it, thanked it for the experience and it went on its way."

NO BREEDING POPULATION

Neither jaguars were harmed. The photographs taken by Glenn and Childs helped win federal protection for the animals as an endangered species the following year and stirred interest from researchers eager to find out about their population and movements.

Childs, his wife Anna Mary and McCain subsequently founded the Borderlands Jaguar Detection Project, a non-profit which set up some 40 to 50 cameras to photograph jaguars roaming through a highland wildlife corridor in the southwest known as the "Sky Islands."

The mountainous archipelago linking Arizona with the Sierra Madre Mountains in northwest Mexico is a unique zone where temperate species like the wolf and black bear mingle with Neotropical animals such as the jaguar and coatimundi, a sociable raccoon-like animal sometimes mistaken for a monkey.

Over the past seven years researchers repeatedly photographed four or five jaguars. They found that all were males straying north from breeding populations in Mexico, a discovery with considerable implications for their survival in the US southwest.