SAN ANTONIO — The U.S. Army is turning to an unlikely weapon in a fight against sprawl in Texas: An endangered songbird.

Camp Bullis is where every medic in the U.S. military will report starting in 2011. It's also smack in the middle of one of the fastest-growing parts of San Antonio, where ranchland has given way to strip malls and pricey homes.

While families learn to live with loud practice fire and Arabic music blared during combat simulations, the Army must cope with brightly lit signs washing out night training and scaled-back artillery to keep neighbors happy. The encroachment has military officials worried that the mission of its 28,000-acre range is at risk.

Enter the endangered golden-cheek warbler: a land-hogging squatter on Bullis, but also an unlikely Army ally.

On Thursday, the San Antonio City Council unanimously passed an ordinance geared toward the little bird whose nesting grounds, the Army says, are being pushed farther onto the 28,000-acre base to make way for new stores and housing developments.

The new ordinance holds developers to greater scrutiny in proving they're not displacing endangered species. The Army says the bird renders potentially one-third of Camp Bullis' grounds as limited or unusable so as to not harm the federally protected warbler.

"He's a pain in the (butt), quite frankly, for us," Paul Dvorak, garrison manager at Bullis, said of the bird. "But he's been the only thing we've been able to put against developers and get them to slow down."

Developers have won virtually every recent standoff with the Army: Only two projects have agreed to submit environmental surveys when it was only at the military's request.

Builders opposed to the ordinance have told city and county leaders that they're following the rules. Warblers have called Bullis home for decades, and they would still be on the post even if development around Bullis ceased, said Michael Moore, past president of the Greater San Antonio Builders Association.

"I think the military needs to give it a rest," Moore said.

Nicknamed "Military City USA," San Antonio boasts Fort Sam Houston, Brooke Army Medical Center, two Air Force bases and nearly 50,000 military retirees. But critics argue the city isn't upholding its reputation when Bullis-area developers leave city meetings victorious.

City leaders say they're responding, pointing to the endangered species ordinance and recent dark-sky rules around Bullis to dull light pollution.

Both sides saw this problem coming. An Army study in the 1990s anticipated it, but plans to address the situation fell by the wayside.

"There's no question that this would have been better addressed in 1995 than in 2009," San Antonio Mayor Julian Castro said.

Camp Bullis trains about 151,000 soldiers each year. That number will grow as combat medics from all service branches report to Bullis in the coming years under the 2005 base realignment and closure process.

Development has literally backed up against Bullis. Satellite television dishes have been found mounted on their fences, and retired Army Col. Michael Ball said he's tossed wayward soccer balls and toys from the training ground over the fence like a backyard neighbor.

Along some edges of Bullis, only a barbed-wire fence divides the training ground and backyard swimming pools. In the 1990s, the area was so remote that only a waist-high ranch fence kept trespassers from wandering onto a post that fires 10 million rounds of live ammunition a year.

The Bullis area is now prime real estate, with the hilly rock outcroppings providing some of the most scenic views in the city. Retired NBA legend David Robinson and country star George Strait are among those who call the area home.

Dvorak said the Army could relocate its training if development continues to be a problem. Castro said that won't happen.

"It's an urban area, and an urban area tends to sprawl," Castro said. "There is a strong resolve to do whatever it takes to protect that mission."