At stadiums across the U.S., public enemy No. 1 is a small, feathery flying machine that weighs about 13 ounces and seems to drop that much in payloads every hour.

The common pigeon is a mad bomber, uncommonly adept at becoming a nuisance.

And, in concert with a squadron of his buddies, he can ruin a day at the ballpark, raining natural bombs from rafters high above and forcing fans to cover their heads and shield food and drinks.

In multimillion-dollar venues with high-priced seats and star-quality athletes, pigeons can steal the show, as they did at a recent Broncos game in Denver.

“It was horrible,” said Allison Harden, who was the target of pigeon poop in the Broncos’ season opener at Sports Authority Field in Denver. “It took all the enjoyment out of the game for me.”

While sitting in her father-in-law’s $250 seats with her husband, Jeff, and other family and friends in Section 306, Harden spent as much time worrying about the next attack as she did trying to watch quarterback Peyton Manning in his Broncos debut. Her mother-in-law, sitting next to her, was hit four times.

“There was a pigeon that was propped up in the rafters above us that didn’t move the entire game,” she recalled. “And my husband was the one who discovered there was a plastic owl up there trying to deter the pigeon, which wasn’t working.

“The people behind us got hit. The woman behind me had a paper bag over her drink.”

The Broncos have vowed to address the problem but, as stadium managers around the nation admit, it’s not easy.

• • •

What happened in Denver is no isolated incident.

In sports venues from Atlanta to Seattle, Cincinnati to Gainesville, Fla., and College Station, Texas, to San Francisco, pigeons and their airborne accomplices -- seagulls, starlings, grackles and bats -- can make life miserable for fans and those responsible for maintaining facilities.

When Great American Ballpark opened in Cincinnati in 2003, pigeons immediately started dumping on customers outside main gates and concourses. At the University of Florida, the school had to build a special bat house to lure bats from several sports stadiums. The Tampa Bay Rays also built a bat house to draw bats from its spring-training stadium, which was being covered in bat feces (guano).

Flocks of seagulls have descended on Comerica Park in Detroit and AT&T Park in San Francisco. Football stadiums at Texas A&M and Georgia have long-standing issues with bats. In 2007, the Cincinnati Bengals, fighting a pigeon problem at Paul Brown Stadium, drew the ire of PETA by suggesting they be allowed to shoot the birds with pellet guns (the city denied the request). At Wrigley Field in Chicago, netting was put up to solve a problem with pigeons.

And, the problem isn’t just limited to the U.S. The Leeds United soccer club in England and Nelson Mandela Bay Stadium in South Africa have solved pigeon problems only through the use of hawks and falcons.

The problem is, stadiums are generally open-air venues and giant invitations for sports and nature to collide -- especially with popcorn, peanuts and unused food littering the aisles.

It’s a free buffet.

“It’s an outdoor facility,” said Charles Whittemore, assistant director of athletics/facilities for the University of Georgia, and the man responsible for keeping pigeons and bats under control at Sanford Stadium. “It’s not sitting in your living room watching the game. That’s part of the challenge. Everybody wants it to be like sitting in your living room watching a game on TV, but it’s an outdoor facility. There’s no way to eradicate it. There’s no way.”

Especially when simply killing the pests isn’t a solution because (A) it’s frowned upon, (B) some species are government-protected and (C) new birds and bats can simply move in to replace the ones killed.

Sports venues will always be attractive to birds and bats, says Whittemore, because the facilities are perfect “condominium living,” he said, laughing.

The animals can get out of the wind and rain, find protected warm nooks and crannies to roost and get plenty of food.

“They’re not coming to see the football game,” Whittemore said of the pigeons at Sanford Stadium. “They’re coming because there’s a food source for them. ... Nature is going to look for the easiest food source, and this is an easy food source.”

• • •

The birds: When the pigeons swooped in on Great American Ballpark, the Cinncinati Reds at first sent out cleaning crews and put up fake owls to scare the birds away.

“That didn’t work,” said Declan Mullin, vice president of ballpark operations. “They sort of laughed at it.”

So the Reds had special netting put up in the problem areas to keep the birds out of spots where their droppings would create problems. Fortunately, said Mullin, it resolved the issue.

At Sanford Stadium, pigeons weren’t roosting in one particular area, but all over a 90,000-seat structure. Whittemore said it has taken diligence to get the upper hand on the birds.

Whittemore and his staff have put up metal spikes to take away roosting areas, they’ve trapped birds and moved them, they’ve scared birds out of areas above seats and walkways and they’ve used electronic hawk and owl calls to scare the creatures out of the scoreboard that provides a cozy hideaway.

The efforts have worked, with the pigeon flock gradually decreasing. Whittemore takes a scouting trek through the facility before every game, and before the most recent one saw about 10 birds. There have been as many as 300 in times past.

Still, the birds are relentless. The “condo” is attractive.

As Whittemore relates, a couple of years ago the staff put up TVs in the sky suites.

“We put the TVs up on a Thursday,” he says. “On Friday afternoon I walked through the stadium and a dove had made a nest on the top of a TV and had already laid an egg.”

In San Francisco, where AT&T Park is next to San Francisco Bay, the Giants have some trouble with pigeons but face a larger problem with seagulls.

The gulls love the free food, and know to show up about three hours after the first pitch to come get it. Sometimes they get overly aggressive and dive toward the seats to pick up food from the ground or pluck it from fans.

“The gulls are generally only an issue postgame because they know the park is a food source,” said Jorge Costa, the Giants’ VP of ballpark operations. “Otherwise they aren’t around. Sometimes if the games run long they get impatient and start flying around.”

He said the gulls are “fast food guys” who get in and get out “and leave the calling cards behind.”

The Giants have used bird distress calls over the public-address system to chase away the gulls, but also got an assist this year from a young red-tailed hawk that moved into the park last November and has stuck around for appearances in 2012. The Giants dubbed him Bruce Lee for the way he attacked pigeons and chased away gulls.

“The hawk comes and goes,” Costa said. “When he’s around the pigeons aren’t.” The gulls will fly at the hawk, hoping to make him go away, but the hawk isn’t fazed.

“If we could get the hawk to take up permanent residence here we would be thrilled,” Costa said. “But when it is here he keeps the animal kingdom in line, for sure.”

• • •

The bats: For many years, Texas A&M’s Kyle Field has been home to hundreds of thousands of Mexican free-tailed bats. They stop on their northern and southern migrations, and many decide to stay.

At times the bat population at Kyle can be enormous. How big? No one knows for sure, but estimates are anywhere from hundreds of thousands to a million, and numerous YouTube videos posted of the bats leaving the stadium at dusk are impressive.

“It looks just like a river is flowing out from underneath the stadium,” said Kevin Hurley, the school’s associate athletic director for facilities.

The bats also just happen to be the state’s official flying mammal, so they’re protected. All the school can do is put up bat netting to restrict certain areas, do extensive cleaning and seal up cracks and crevices.

But with so many bats, winning the war is impossible. Progress comes only in small steps.

“That’s the thing,” Hurley said. “It’s like trying to spoon the ocean out with a teaspoon.”

“You can’t go kill them, you can’t go poison them, you can’t do anything like that, so you literally have to prevent the bats from roosting, nesting, living in the area where you’ve got fans,” he added. “It’s been a true mammoth effort to clean. After the fact you clean, you just try to get as much refuse out as you can, you hose things down, you spray things that kill the smell and kill the bacteria that creates the smell.”

Hurley said it’s a constant fight. Bats move into an area, mess it up and bother the fans, then the staff cleans it, puts up netting and waits for the bats to pop up elsewhere.

“All we’re doing is pushing the problem to different areas of the stadium in the short term,” he sid.

The only good thing?

“We don’t have a mosquito problem,” he said. “They take care of a lot of insects.”

Bats are a particular problem in the South, as Whittemore at Georgia can attest. The three types of bats at Sanford Stadium will roost over seating areas, dropping guano, and will create a stink by squeezing through cracks into open spaces behind walls. So, just as at Texas A&M, the staff at Sanford has to seal off roosting areas.

“These little suckers can get through any kind of crack and get behind a concrete block wall,” Whittemore said. “I mean, that is penthouse living right there. ... That’s perfect. It’s going to be nice and warm, it’s out of the weather, they don’t have to worry about any creatures coming to get them. ...

“But they still go to the bathroom in there and the smell is pretty bad. We’ve actually had as much problem with the smell of bats that you can smell when you walk by this block wall.”

• • •

The problem-solvers: For about 15 years, Bird-B-Gone, a company in Orange County, Calif., has been helping schools and teams control flying pests. They provided the bird netting at Wrigley Field, have spikes on potential pigeon perches at Yankee Stadium and handled a bat problem at Ole Miss, among many others.

Pigeons and seagulls are first and second on the list of avian troublemakers they’re hired to deal with, but they also provide netting to control bats.

Most of their work involves fixing problems that crop up at existing venues, but increasingly new facilities are including bird and bat control into their planning, said Zander Brown, the company’s director of marketing.

Brown said there are only three proven items to thwart birds: netting, spikes and electric tracks (strips that provide a mild electric shock).

Netting is the best long-term solution, he said.

“It’s the most expensive route to go, but it lasts the longest and it’s total exclusion,” he said.

The issue, particularly with pigeons, won’t ever go away.

“Stadiums are in urban areas,” he said. “That’s the common issue.”

• • •

When Harden experienced the bombardment at the Broncos’ opener, she remembers thinking it was so uncomfortable she might never want to come back to another game.

She was dissatisfied that the Broncos wouldn’t address the problem that night, and angry enough to go to the media to air her story.

Since then, however, she said team president Joe Ellis called her to apologize and assured her the team would fix the pigeon problem in Section 306. Her father-in-law was also told the team would put up netting to keep the birds away. The team also released a statement saying it takes the safety and comfort of its fans seriously.

This week, Harden said she hopes the fact she spoke up will allow them to “be a part of the solution.”

But when it comes to birds and ballparks, it’s never an easy marriage.

“I know people say, ‘You’ve got to do something,’” Georgia’s Whittemore said. “But it’s an outdoor facility. It’s nature. There’s a lot of things we can do, but we can’t get rid of them all.”