Members of Águilas del Desierto — Eagles of the Desert — gathered before dawn one July morning in San Diego for a foray along the Mexican border. Their mission: to find the bodies of immigrants, hundreds of whom die in the desert each year.

Illegal crossings are down sharply on the southwest border, but the number of people dying is climbing. At least 412 migrants were found dead in 2017, up from 398 the previous year. Exposure to extreme heat or drowning in irrigation canals causes many of the deaths. With the expansion of the Border Patrol pushing immigrants further into remote territory, forensic researchers say the number of deaths may be much higher. As the search began, temperatures were approaching 100 degrees, and wildfires scorched the desert nearby.

The Águilas scoured a stretch of federal land that was both desolate and futuristic; huge wind turbines towered above the brittlebush. Normally, the group searches in remote parts of Arizona, but this quest was only an hour from San Diego.

“I know the agony of losing a loved one to the desert,” Eli Ortiz, the group’s leader, said. He found the bodies of his brother and cousin in 2009.

Most Águilas are immigrants themselves. They find purpose in providing closure for families haunted by missing relatives. They’ve undertaken this gruesome task once a month for six years.

The desert around the Carrizo Gorge Wilderness is vast and forbidding, the group’s planning was meticulous. They used satellite images, GPS mapping and intelligence gleaned from Border Patrol agents and smuggling networks.

Occasionally, family members who contact Águilas on Facebook go along. Rafael Luna, 50, said his brother went missing two months ago after setting out from Jalisco in western Mexico. “He was left out here to die,” Luna said.

José Genis González, 33, is a Navy vet, and trained as an EMT. He crossed with his parents when he was 2. After another volunteer picked up the scent of a dead body, González rushed to what turned out to be a grisly scene.

There was a body decomposing in the desert. Careful to avoid disrupting the remains while authorities were called, volunteers used gloves to examine the scene.

Next to the body, they found a prayer card with the image of St. Peter, thought to protect migrants from harm, and a Mexican ID card bearing the name of Adrián Luna, Rafael’s brother.

Luna began shouting, “My brother, my brother!” before collapsing on the desert floor. His wails echoed across the empty hinterland.

Agents from the San Diego County medical examiner’s office recovered the body. Coroners sometimes carry out DNA testing to definitively identify remains.

Migrants perish in the desert from dehydration, hypothermia or heatstroke. Some are raped and killed by smugglers. Rafael Luna doesn’t know how his brother died, but people in Adrián’s group told him where the body could be found.

Volunteers placed a simple wooden cross where they found the body. “The desert is like a lion, stalking both the strong and the weak,” said Ortiz, the leader of the Águilas. “The desert could devour any of us.”