The live training exercises that take place on the nearly two-million-acre bombing range near the border here are as realistic as can be. Jets swoop down to take out enemy tanks. They strike mock airports or terrorist training camps. The terrain, with its vast expanse of desert scrub ringed by rugged mountains, could be a far-away hostile place, as veterans of American conflicts in the Middle East who have used the range can attest.

“Having flown over Iraq during the first gulf war, the range very much resembles what I saw,” said Jim Uken, a retired Air Force colonel and fighter pilot who is now the range director.

But there are things about this battle zone that set it apart. Take the Sonoran pronghorn, for instance, an endangered animal that wanders into the bombing zone from time to time and forces pilots to hold their fire. Or the illegal immigrants and drug smugglers who also sometimes interrupt operations by ignoring the warning signs posted on the periphery of the range and crossing through this most dangerous stretch of land on their way north.

Such incursions are declining, though, meaning that more often than not, it’s bombs away.

Every morning at sunrise, biologists peer across the range with binoculars to search for pronghorn. Their coordinates are radioed in to headquarters at Luke Air Force Base, and if any animals are observed within a kilometer of a target, exercises are called off or shifted to another range. Disruptions are down, mostly because the military had previously considered an antelope anywhere within three kilometers of a target to be in danger.

“Aircraft are much more accurate today,” Mr. Uken said of the policy change, noting that pronghorn populations have increased from less than a few dozen a decade ago to nearly 200 now, divided between the wild and a captive breeding program at the adjacent Cabeza Prieta National Wildlife Refuge.

Fewer migrants are being spotted on the range, as well. In the 2011 fiscal year, which ended Sept. 30, there were 21 human incursions on the Air Force’s part of the base, which caused operations to be suspended for a total of 55 hours. That is down considerably from 2008, when 40 incursions resulted in 202 hours of delays. The numbers were even higher in the mid-2000s, said Mr. Uken, who has overseen the range since 2000.

Those numbers coincide with declines on the Marine side of the base, which abuts the Mexican border, and the overall picture in Arizona, federal officials say. Customs and Border Protection officials recently reported that the number of illegal border crossers arrested in Arizona was at the lowest level in 17 years. The Border Patrol’s 129,118 apprehensions in Arizona in the 2011 fiscal year represented a 41 percent drop from the year before, officials said.

Crossing over the border even in those parts of the state not controlled by the military carries a plethora of risks — from rattlesnakes slithering on the desert floor to hostile temperatures that can swing from blisteringly hot to bone-chillingly cold. But the dangers here, which can take the form of 2,000-pound bombs dropping from the sky, are on a whole different scale.

“Some of these coyotes are pretty unscrupulous,” Mr. Uken said of the smugglers who lead migrants north. “They will take a group across and then slip away, leaving them. They will say that Interstate 8, which is everyone’s goal, is just over that ridgeline. They won’t mention what’s in between.”

In some areas, fighter pilot trainees use dummy bombs to test their accuracy. In some tactical areas, like the one used by Britain’s Prince Harry during his recent Apache helicopter training at the Goldwater Range, live explosives are shot from the sky.

Like Hollywood set designers, technicians work on the ground to create targets that resemble those found on real battlefields. There are mock airstrips with planes parked nearby, mock industrial yards and surface-to-air missile sites. Wrecked cars, tanks, buses and other vehicles are placed in the desert, like an out-of-the-way parking lot.

Related posts:

1. Texas Mayors Differ on Using War-Zone Equipment Along Border The Send Equipment for National Defense Act, written by...
2. The Battle Over Aviation Emissions Much is at stake for Europe, which has sought...
3. Orlando Bosch, Cuban Exile Acquitted in Jet Bombing, Dies at 84 MIAMI — Orlando Bosch, a prominent Cuban exile who...