Robles moved out to the ranch when he was 27, with his wife and young son (they now have three kids), after studying agriculture at the University of Guadalajara. In 1987, he became the owner of his 10,000-acre portion. (Eduardo and a cousin also have 10,000 acres each.) He grew increasingly disenchanted with the impacts of grazing and recurring droughts. Even when ranching was profitable, he says, "You are only living the life of overgrazing." In 1991, he sold his cattle and started leasing his land for other ranchers' cattle, and in 2000, he began reducing the number of cattle in the leases -- dropping to 150 by 2008, 50 in 2010, and briefly -- in 2011 -- hitting zero. (To supplement the family's income, his wife runs a hotel in Magdalena, a 45-minute drive away, where Robles helps out when he has time.)

A U.S. conservationist encouraged Robles' venture into conservation ranching. At a 2000 meeting in Hermosillo, the capital of Sonora, Tom Wood, co-director of the Southeastern Arizona Bird Observatory, a nonprofit group that aims to "conserve the region's birdlife through research and public education," sought to educate Sonora's ranchers about the possibilities of ecotourism. None of the other ranchers were as intrigued as Robles, who came up to Wood afterward and asked, "How quickly can we do a bird inventory?"

Eduardo Limón, a freelance biologist and ornithologist in Hermosillo who also attended the meeting, visited the ranch soon afterward and was surprised by its good condition. Robles was already rotating cattle to keep any area from being grazed too long. That year, Robles also installed a couple of remote cameras on his ranch to photograph wildlife. Limón saw impressive habitat and counted about 140 bird species. He called the Sonoran Joint Venture, an organization of government agencies and nonprofits based in Tucson, whose mission is to conserve borderlands birds and their habitats. Since the Joint Venture shares an office building with the Tucson Audubon Society, word of mouth soon brought many U.S. birders to the ranch, along with a host of U.S. Fish and Wildlife Service fish, bird, reptile and mammal specialists.

"I went down a couple of years later (during a dry spell) and the headwaters of the stream was bubbling up out of the ground, and the stream was flowing well," says Wood, whose organization has sponsored eight ecotourism trips to Aribabi. "I was amazed."

During the mid-2000s, the Joint Venture, which is staffed by wildlife service biologists and governed by a board of researchers, bureaucrats and conservationists, included Robles' ranch in a study of important bird habitats. In 2003, it gave him a further boost by paying $30,000 to fence off Río Cocóspera from cattle. Even before that, Robles' riverfront vegetation was in the best shape of the 20 areas studied, recalls Robert Mesta, the Joint Venture's coordinator. "The other areas in Sonora that we studied were hammered. Other than large cottonwoods and willows, there was nothing left. His was still pretty lush ... despite the fact that it had been grazed," Mesta says.

Once the stream was fenced, the grasses and shrubs grew up to six feet high. The bird life increased to 180 species, says Limón, who conducted monthly surveys from 2000 to 2010. New arrivals included the summer tanager and the Sinaloan wren.

Robles had to jump through some hoops to get the Mexican government's permission to sell deer hunts. There is virtually no government regulation of ranching in the country, but Robles was an early participant in an innovative Mexican conservation program: Unidades para la Conservación, Manejo y Aprovechamiento Sustentable de la Vida Silvestre, better known as the UMA program. Created in the 1990s, it encourages ranchers to work with biologists to create plans for managing wildlife in sustainable ways that also make a profit, such as selling hunting opportunities. (Since the UMA program began, hunting is legal only on UMAs.) Robles won approval as an UMA in 1998 and began selling hunts.

Robles also benefitted from an extraordinary  relationship with the Sky Island Alliance, a Tucson group that seeks to restore and protect the biodiversity of mountain ranges on both sides of the border. It began when a Sky Island Alliance biologist, Sergio Avila, came to the ranch in 2006 while scouting for jaguar habitat, trying to track the origins of the jaguars that occasionally appeared in Arizona. Avila, a Mexico native, says that Robles "was already using phrases such as 'ecological processes' and 'conservation in perpetuity,' and I thought, 'Who is this guy?' Then he comes out with a folder containing a bunch of photos, of bobcats, mountain lions, black bear, deer and coati, and told me he had two or three remote cameras already."

In February 2007, Robles let Avila's group set up six more cameras on the ranch. (Eventually the total grew to 12.) The cameras have documented seven ocelots -- the northernmost known breeding population -- and two jaguars, as well as bobcats. Later that year, Robles signed an agreement with Sky Island Alliance in which he promised not to kill predators or poach wildlife on his land. In return, Sky Island agreed to promote the ranch -- in the media, in the group's writings and on its website -- and to collaborate with Robles in monitoring wildlife and to support restoration activities, such as water pumping for wildlife. Avila and other Sky Island staffers became the ranch's most enthusiastic U.S. advocates, leading more than 30 field trips and conducting wildlife tracking and restoration workshops. The group has also built rock dams along creeks to slow flows and encourage vegetation growth, and has helped conduct biological studies here.

Ornithologists, herpetologists, mammalogists, ecologists and other biologists from Mexico and the U.S. have come here to research many species, including the endangered Gila topminnow and Sonora chub, the lowland leopard frog, and the Tarahumara salamander (a population that Robles discovered). University of Sonora biology students visit to learn to use remote cameras and do other research. High school students and Boy Scouts from Sonora, along with a Border Studies group of students from Earlham College in Indiana, have done restoration work here, building at least 15 of the small rock dams that encourage wetlands.