SANTA RITA MOUNTAINS, Arizona (Reuters) - Jaguar biologist Emil McCain stoops over a remote-sensing camera attached to a tree in these rugged mountains a few miles to the north of the Arizona-Mexico border.

The researcher is checking for images of a handful of extremely rare jaguars that prowl up from Mexico over mountain trails in some of the wildest country in the southwest, although they are now under threat.

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 U.S. government to curb it: building fences.

In this election year, Washington hopes to complete 670 miles

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 border, despite opposition from some landowners and environmentalists.

“The low flat valleys are effectively walled off to wildlife. As a result everything is funneled 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 funneling

of people into the last remaining habitats. Jaguars are very solitary animals, they can’t move freely where there are a lot of people.”

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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.

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Childs, his wife Anna Mary and McCain subsequently founded the Borderlands Jaguar Detection Project, a nonprofit 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 U.S. southwest.

“Because there are no females and no reproduction, jaguars in the United States are totally dependent on cross-border movement,” Said McCain. “That connectivity with Mexico is absolutely crucial.”

UNCERTAIN FUTURE

As the construction of barriers continued to pressure that connectivity, the U.S. government decided at the start of the year to abandon the recovery of jaguar populations as a federal goal, further calling into question the future of the animals.

McCain says he is concerned that there is no conservation plan to protect the big cats and their core habitat in the United States, which, he says, leaves them increasingly vulnerable should any decision be taken in the future to secure remaining areas of the border with fencing.

“After the Border Patrol finishes securing the lowland areas they will be forced to extend those walls out across the mountain ranges and totally seal off any hopes of jaguars crossing back and forth,” he says.

While jaguars would not die out as a species -- fewer than one percent of their total number live in the United States -- losing this elusive predator would signal a retreat on protecting this fragile borderland wilderness for posterity.

“The jaguar is a great emblem of wildness and an example of a healthy ecosystem,” McCain said.

“It really inspires people and creates a sense of wonder at the natural world. And in today’s world, we really need that.”