Historically low numbers of people are crossing the border illegally into Southern Arizona this year, but they're still dying at historically high rates.

In the 10 months through July 31, remains of 161 suspected illegal immigrants have been found in Southern Arizona from New Mexico to the Yuma County line.

That puts this year's death toll on pace to end up at about the annual average for the last decade - 197 - even though that period includes years when there were three to four times as many attempted crossings.

That means the rate of border deaths so far this year - the number of deaths per 100,000 apprehensions - is at about the record high set last year, 154. Illegally crossing the border into Arizona is riskier than it's ever been.

Experts point to a few factors keeping the death rate up.

With the border harder to cross, "smugglers will guide illegal aliens through more remote, harsh terrain to avoid detection by law enforcement, which increases risk of death," U.S. Border Patrol spokesman Brent Cagen said in a written response to questions.

Another possible factor: Central Americans seem to be a growing proportion of those crossing the border illegally. They may arrive at the U.S. border already in greater distress than Mexicans who are just leaving their home country, said Geoff Boyce, spokesman for No More Deaths, a group that patrols areas southwest of Tucson to help migrants.

Also, not every set of remains may be from a recently deceased person.

Joe Adams and his crew have found at least two sets of remains in the last couple of months. Adams, a St. Louis private investigator who leads a border-watch team in the area south of Three Points, reported a woman's decomposing body in early May.

Mariana Chaverri Piña had died in the previous few days. But they also found the bones of at least one person in July, and it was unclear how long that body had been there.

"In 2011, nearly half of all discoveries of deceased individuals were those of skeletal remains," wrote Cagen of the Border Patrol.

frantic phone call

Just last week, a family in Waukegan, Ill., was urgently calling authorities in Arizona, begging them to search for their lost loved one. It's a phenomenon that happens here all summer as the heat takes crossers down.

Jaime Pasillas, 42, a father of four American-citizen children, had returned to Mexico earlier this summer to renew a 10-year visa, his family said through announcements from the League of United Latin American Citizens. But his renewal was rejected, and he decided to return illegally.

On July 30, Pasillas called his family to tell them he was crossing from Sonora into Arizona with a "coyote," or smuggler, and would arrive in three to five days, but then they heard nothing. On Aug. 9, family members spoke with the last person known to have seen Pasillas alive.

The picture he painted was painful: Pasillas' feet were wounded in the crossing, and he was lagging behind the group. On Aug. 6, the guides left Pasillas in the desert around Santa Rosa in the northern Tohono O'odham Nation, with a gallon of water. The high temperature that day in Ajo and Tucson was 106 degrees.

Family members came to Southern Arizona to try to help find him, and Julie Contreras of LULAC urged tribal authorities and the Border Patrol to search. The patrol did prepare to launch a search early Aug. 13, but then they found out the O'odham police had found a body three days before.

While final identification has not occurred, the family has identified Pasillas by a tattoo. Now they are working to get his body returned to Waukegan.

At border, in distress

Some crossers are arriving at the border already in medical distress.

Tucson-based Humane Borders is setting up water stations in Mexico, in cooperation with Mexican authorities, because some migrants have walked so far before even crossing the border into the U.S.

"Many people that are trying to cross are going to points extremely far east or west of the main crossing areas while still on Mexican soil," said Bob Feinman, a board member of Humane Borders. "By foot these can be a couple or three days."

Indeed, agents in the Border Patrol's Tucson Sector are on pace to carry out about 13 percent more rescues this year than last, when they recorded 500.

No More Deaths members, who work in the broad area around Arivaca, have seen the same trend, Boyce said. Migrants walk west from Nogales for a day or two to get into the better-hidden canyons and washes before cutting north into the United States.

"By the time people get to where we're going to see them in our work," he said, "it adds that much more strain and environmental exposure."

On StarNet: Search the Border Death database at azstarnet.com/borderdeaths for the names of those who have died attempting to cross the border from Mexico.

Rate of death rises

The number of people trying to cross the border into Southern Arizona illegally has been plummeting, but the number of people dying in the process is not. The reason: It's more risky to cross. This chart shows the number of bodies found in the Tucson Sector per 100,000 Border Patrol apprehensions. While apprehensions aren't a direct measure of crossings, other measures have also shown migration is extremely low.

Year Number of deaths per 100,000 apprehensions

2004 39

2005 52

2006 46

2007 59

2008 57

2009 88

2010 119

2011 154

2012* 153

* Through July 31

Contact reporter Tim Steller at 807-8427 or tsteller@azstarnet.com