In the dusky late afternoon sun, 1.5 million Mexican free-tailed bats take flight from underneath the Congress Avenue Bridge during Austin’s spring and summer months. Austinites will celebrate the natural phenomenon at Austin Bat Fest on Sept. 6, an annual tradition featuring live music, local cuisine and crafts.

“You know the bats are there, but you don’t ever take the time out to go see them,” said French Smith, the founder of Austin Bat Fest. “When there’s a festival going on, … there’s a little more to do besides just seeing the bats.”

The celebration, now in its 19th year, will take place from 3 p.m. to 11:45 p.m. and feature an array of live music, including Silversun Pickups, Giovannie & The Hired Guns and Waka Flocka Flame.

“We try to keep current with what the kids are listening to, and I think we’ve done a good job on that this year,” artist booker Adam Brewer said. 

Brewer said one highlight of this year’s lineup is Zak Loy, a local musician who has been performing in Austin since age 13.

“He’s a hometown hero,” Brewer said. “I’m just so excited to have him premiere his solo act. He’s done so much for the Austin music scene, and now he’s a globetrotting superstar touring with the band Live.”

The guitarist will return to play his debut solo album, Dinero, at Bat Fest at 4:20 p.m. after playing across the country with bands such as Damesviolet, Alpha Rev and Mother’s Anthem.

“Austin is a special place for me,” Loy said. “I grew up playing music in Austin, so I have a different level of attachment. It’s a homecoming for me. … Some fans have been watching my career over the last 30 years. 

During performances, audiences can look to the skyline to see the bats take flight. Smith said the idea for the festival first came to him when he saw a music festival on the First Street Bridge in 2003. Later on, he realized how many people came to the area to see the bats.

“They’re here in the biggest numbers in the summer because this is when they reproduce,” Smith said. “By August and September, the young bats are also flying out to catch a meal with the adult bats, so you have the largest numbers coming out this time of year. It’s the best time for viewing the bats.”

Smith said the bats emerge from under the bridge and fly out in a close-knit stream formation.

“We want people to see that bats are all right,” Smith said. “They do a lot of good. (It’s a) reminder that they fly out from that bridge and go to agricultural areas. All night long, they’re feeding on things that feed on our crops.”