Crystal Kitty is correct. There are more bats under the IH35 bridge over McNeil Rd than downtown under the Ann Richards Congress Ave. Bridge. But that doesn't mean you won't see them there. There are still a lot of them. They will be around until at least November. Then it's off to Mexico. (They are, afterall, Mexican Freetail bats.)
The McNeil bridge has a lot less traffic near it. There is a store or crafts shop on the NE corner you can park in. Decent place to watch.
The bats were coming out very early, before dusk, when the heat was on. Lately they have been coming out right about dusk. I saw them fly last week, downtown.
Originally Posted by NipLover
The bats fly out of there heading to the east. They mostly come out on the south end of the bridge. The store is a NAPA auto parts store. You can park at the auto parts store, and then walk down to the south end of the bridge. It's best to stay outside the NB frontage road to watch. Expect the ammonia stench of bat droppings.
There are actually bats there year round, but fewer in the winter.
Don't do anything stupid like stand on the railroad track or wander into the frontage road, or touch any grounded bats. (It sounds stupid, but people do it, and be especially careful with kids who might be distracted by the bats.)
The last time I saw them, they were about a half hour before sundown, but I don't know how consistent this is. Flight time might vary with the moon phase, temperature, etc.
I don't know how the number of bats at that bridge compares to Congress avenue.
There are also bat colonies at the Mays Street bridge over the railroad track in Round Rock, and under the northmost bridge over Lamar at 183. There's also a colony at Kyle on I-35 over Bunton Branch sort of behind the Lowe's store.