It’s officially time to see bats starting their nightly hunts in Austin

One quintessential Austin experience is watching the sun set over the lapping waters of Lady Bird Lake while listening to the high-pitched, yet subtle, chirps of the tiny bats that call the Congress Avenue Bridge home.

It’s that time of year again when the urban colony of about 1.5 million Mexican free-tailed bats comes home to roost underneath the downtown-adjacent bridge, and people in Austin are able to start watching them leave for their nightly hunts. Lee Mackenzie, Austin Bat Refuge manager, told MySA the majority of the bats migrated back to Austin from Mexico the third week of February, but about 60,000 stayed in Austin over the winter.

“At this point, it seems that the summer colony’s probably all back by now. My understanding is that some mating goes on in Mexico, but another round of mating happens around Congress Avenue Bridge during March,” Mackenzie said. “So, March is kind of like a big party time at Congress Avenue Bridge.”

Mackenzie said March and April are some of his favorite times to watch the roughly 750,000 bats fly out of the bridge at night to hunt for insects. Because they usually fly out in mass close to dusk, the furry creatures can be easily seen against the backlight of buildings across the water. The colony usually flies out later at night in May and June, but this time of year has less bats because the babies haven’t been born yet.

“If they fly less than 15 minutes after sunset, you’ll get a good view from the top of the bridge. But any later than that, you’re probably just going to see dark bats against dark water,” Mackenzie said. “So we recommend the South Lawn on the southeast side of the bridge going under the bridge. You can always see bats down there, and you won’t get skunked. Going under the bridge is the best view.” 

During their mating season, all the female bats will give birth to one baby, with the average date of birth being around June 10. Those pups will nurse for six weeks until they’re strong enough to try stretching their wings out on their own, which usually happens by late July. 

“Late July, the babies … start stretching their wings and doing little push-ups to try and get their wings nice and strong,” Mackenzie said. “Eventually the time comes where … they just got to fly. That first drop out of the bridge is pretty momentous for them, and they’ve got 40 feet to figure out how to fly. They’ve got that next hour or two to figure out where to go, follow their moms out to hunt, not get eaten by a hawk or owl.” 

That time of year is not the most recommended to see the bats leave for their hunt because the parents are very protective of their young, meaning they’ll wait until it’s darker to leave so they have less chances of being attacked by a predator. There’s also a greater abundance of insects in the summer months, so the bats get a little lazier about leaving early, Mackenzie said.

“They can just sleep late and wait till after dark and then fly out when it’s safe and still fill their bellies and eat almost their body weight in insects every night when they’re lactating,” Mackenzie said. “These bats here are doing a huge ecosystem service for us by knocking down huge numbers of crop pests, saving us billions of dollars in pesticides we don’t have to buy and crops that won’t get ruined by the pests. They’re just a vital part of the balance of nature. And we get to watch them.”  

The busiest time of year for bat viewing in Austin is usually August to September, when a lack of regular rainfall means that there are less insects hatching, so the full colony of bats will hunt earlier because they have to fly further and for longer periods of time to find adequate food. 

Eventually, the majority of our flying friends will migrate south to Mexico around October and November. But don’t worry, they’ll be back.