TUCSON, Ariz. (AP) -- Illegal border crossings have dwindled so much in southwestern Arizona that Marine Corps pilots rarely have to abort practice bombing runs any more on their vast desert target range.
Illegal immigrants hiking through the desert have long created problems for military air operations on the 2,700-square-mile Barry M. Goldwater Range, which butts up against the U.S.-Mexico border in some areas.
In the past, intruders have forced Marine pilots to divert their AV-8B Harrier jets to other target areas or to land without completing their missions.
But enforcement and technology mean intrusions have virtually ceased on the westernmost part of the range used by the Marines.
"It's borderline nonexistent," said Ron Pearce, the Corps' range management officer. "I would say there have been zero flights canceled this year," with only slight delays.
The isolated range has been a crossing point for years for illegal immigrants seeking to avoid more heavily patrolled stretches of the U.S.-Mexico border. There have been no reports of immigrants being struck by military ordnance.
The Border Patrol doesn't keep apprehension statistics for just the Goldwater Range area, but figures for the region that includes it show apprehensions have been dropping. Federal authorities attribute that in part to more stringent enforcement and to fences and other barriers erected in southwestern Arizona in recent years.
Dan Stein, president of the Federation for American Immigration Reform, which favors tougher immigration enforcement, said ramped up interior enforcement and the abysmal job market are major reasons for the drop-off.
"But certainly these are promising trends," Stein said. "Surely this facility was set up to provide training for military personnel, not a highway for illegal aliens."
Stein said interruptions in military training and efforts to track down illegal immigrants have been "a huge drain on taxpayer resources ... It's overall a very promising development, the fact that it's trending down."
Trespassing on the range had started becoming an issue in 2003 and 2004, said Pete Loughlin, the Marines' mission assurance director.
The Corps didn't start tracking the effects on training until April 2005. During the following six months, 166 two-plane training flights were affected, or 3.8 percent of a total of 8,739 individual flights.
The Marines responding by installing a ground-based radar system, and the Border Patrol installed 37 miles of border fencing and vehicle barriers.
The Marines also established a range operations center that helped them track where missions were being flown so the entire bombing range didn't have to be shut down while Border Patrol agents were conducting a search.
"By the end of fiscal 2007, we had solved our problem ... we stopped reporting, because our particular challenge was solved," Loughlin said.
The same isn't true for the Air Force, which uses 1,600 square miles on the eastern side of the same range to train pilots flying F-16s out of Luke Air Force Base in Glendale, Ariz., and A-10s out of Davis-Monthan Air Force in Tucson.
Figures show migrants affected more sorties for more hours last fiscal year on the Air Force side of the range than earlier. But the increase hasn't been significant, said Kevin O'Berry, the Air Force's intergovernmental liaison for the Goldwater range.
"Even though the numbers show an increase, in the big scheme of things it's just a fairly steady state of disruptions," he said.
Even search-and-rescue efforts "have less of an impact than weather," O'Berry said. "And we have great weather."