By Nadia Drake of Nature magazine

Every year, thousands of undocumented migrants make the dangerous crossing from Mexico to Arizona in the United States through the Sonoran Desert. One anthropologist is hoping to demystify these clandestine crossings by collecting discarded belongings and mapping rest stops, and analyzing these using scientific methods.

In the United States, debate about illegal immigration is colored by myth, misconception and a paucity of scientific data, says Jason De León, an anthropologist at the University of Michigan in Ann Arbor.

"We've talked about migration quite a bit in academia, but it's mostly sort of sociological or reliant on survey data after the fact," says De León. He estimates that around 200 people die near the border between Arizona and Mexico each year.

Just trying to do research in such an environment hints at the hazards of migration. "I've gotten out there, gotten in trouble, just borderline about to have sunstroke or something like that. You get a sense of how difficult it is," he says.

Since 2008, he has analyzed around 100 sites used by migrants for rest stops in a roughly 50-kilometre stretch of desert between Nogales, Mexico, and Arivaca in Arizona. Working with students, he maps each site, notes what it was used for - whether people have made beds, for example - and records all the discarded objects. He has collected more than 6 tons of items, including backpacks, shoes, first-aid kits, clothes and water bottles.

Such artifacts help De León identify trends in migration and estimate the number of people making the journey. The presence of women's and children's shoes, for example, shows that it's not just adult men crossing the desert.

Nearer to Arivaca, sites become larger and clothing and backpacks replace food packaging in the litter. "Their guide will say, 'Ok now you gotta clean up. You look like you've just walked through the desert.' So you change your clothes, brush your teeth, wash your face - that's when you get a lot of this stuff left behind," De León explains. He presented his findings at the Society for American Archaeology's annual meeting in Sacramento, California, on 1 April.

Blood, sweat and tears

De León has also spent months in a migrant shelter in the Mexican border town of Nogales, interviewing those about to begin the journey through the desert and those recently deported back to Mexico.

In total, his data show that migrants circumvent stricter border controls -- such as increased patrols or fences -- by using routes that are more remote and dangerous. "Enforcement strategies that create suffering and death are clearly no match for the hunger and poverty that drive migrants to the United States," he says.

"This is a groundbreaking type of research. De León is pushing the archaeological envelope," says archaeologist Ran Boytner of the University of Southern California in Los Angeles. "His research will have a very strong impact, both in and out of the discipline. It takes a lot of guts to do what he's doing."

De León now anticipates expanding his survey areas in Arizona, and possibly including sites in California, Texas and New Mexico.

Studying these objects humanizes undocumented migration, says José Antonio Lucero, a political scientist at the University of Washington in Seattle. Most people don't understand what drives a person to leave his or her home and embark on a risky journey.

"Jason can say a lot about the whole experience through the artifacts and the folks he meets," he says. "It's a world that we don't know very well. I hope the project leads to a more enlightened conversation about immigration."

This article is reproduced with permission from the magazine Nature. The article was first published on April 11, 2011."