On the night of March 25, 2019, it happened again. The fans looked at the sky in horror. A wall of white pierced the pitch black night. There was nowhere to hide.

The seagulls had returned to Oracle Park.

That's when the clapping began. Loud, incessant clapping. A chant spurred them on: "Everybody clap your hands." The park filled with the undeniable sounds of DJ Casper AKA Mr. C The Slide Man's anthem "The Cha Cha Slide." Clap-clap-clap-clap-clap-clap-clap-clap. Nearly at once, in formation, the birds flew east past McCovey Cove, disappearing into the darkness, gently into the night.

Upon witnessing this scene, KNBR wondered: "Are the Giants using the Cha-Cha slide to scare seagulls away from Oracle Park?"

The answer, SFGATE can happily report, is yes.

"We use the audio prompts (to deter the seagulls)," said Alfonso Felder, the Giants vice president of administration. "These prompts, combined with crowd noise, can be effective in dispersing the seagulls in moments when they become highly visible."

The birds are a familiar sight for those who have attended a professional baseball game in the Bay Area. As a Giants or A's game winds to a close, a coterie of gulls might swarm the park. They hunt for fries. They hover above the stands. When a particularly menacing squadron flocks near your seats, you have a clear choice: stay in our seats and risk a bird poop bath, or run for cover. Millions of paying individuals — ostensibly there for merriment — must make the choice for themselves each year.

Felder, along with Jorge Costa, leads the Giants' gull deterrence efforts. He remembers 2013 as a tipping point. The Giants were hosting the sport's preeminent international tournament, the World Baseball Classic. Felder remembers an unusually large number of birds in the stadium and a number of comments from fans.

So they began conducting research. They spoke with "bird abatement" companies. One option that wasn't available for eliminating the birds: shooting them. Federal law says it's not allowed.

"There are all kinds of approaches that people take, ranging from physical devices that involve light or sound, to more natural approaches that involve predatory birds," Felder says. "All of them have ups or downs, and I think we've been fairly careful about what advice we've taken. We want to make sure whatever we do is both safe from the perspective of people and birds, and also humane."

At first, Felder could not understand why the birds seemed to gather with greater force while the Giants were pitching. The outfielders, he said, were distracted.

"I'm afraid of them dropping something, using the bathroom on top of me," outfielder Denard Span told the Associated Press in 2017. "Or maybe them dropping some food near me and then all of them just freaking swarming me."

"We quickly came to the realization that it had to with noise," Felder says. "When we were at-bat, obviously, every announcement of a batter, every positive play on the field, when the home team is at-bat generates significant applause, and so as a result, it was clear that the difference in terms of sound within the building was what was causing that dynamic."

Enter, then, the Cha-Cha slide, a humane and hilarious solution to a mildly annoying problem. (Felder notes that the bird issue is not "significant" in the team's eyes.)

Across the Bay, the A's employ their own innovative strategy. In 2017, vice president of stadium operations Dave Rinetti noticed that the stadium was seeing an increasingly large share of birds during day games. Rinetti spoke to a local company and paid a "few hundred dollars" for a falcon-shaped kite, which the team named Falcon McFalconface. They hung it high in the bleachers and saw initial success, so they bought another one. Falcon McFalconface and his pal, Scott Hattibird, still fly high above Oakland-Alameda County Coliseum.

Why do the birds seem to know when the game is ending? It's a question without a clear answer. KQED spoke with a number of experts in 2011, who landed on a number of explanations. One cited the lights. Another thought it had something to do with the crowds leaving early. But all seemed to agree: These birds are pretty smart.

"They seem to have a sense of how long games normally go," Dan Murphy, a volunteer with Golden Gate Audubon, told KQED in 2011. "It's likely that a few birds are always watching and as soon as a few birds go in, others will follow. They're really good at what they do. They find food sources and use them to the max."

Felder and the Giants, then, are dealing with a sophisticated nemesis here. But with the Cha-Cha Slide, they seem to have found that Goldilocks solution: cheap, effective, and humane. It's working — for now. We'll see how the seagulls counter.

Michael Rosen is an SFGATE homepage editor. Email: michael.rosen@sfgate.com.