We had to privilege to experience some amazing Mexican free-tailed bat emergences in Austin over the Memorial Day weekend. The bat colony under the Congress Ave. bridge just south of downtown Austin is well known. Hundreds of people show up to watch every night, and on busy nights, that can be thousands. You will see every age, sex, culture and race there to see the bats. They have become a popular destination for folks coming to Austin. Over two million bats live in that bridge, the largest urban bat colony in the world.
We were there on a busy Saturday night – the park and lake below the bridge were filled with people. At this time of year when female bats typically have young, the Mexican free-tails often emerge earlier than sunset so they can get out and start feeding. There had been a lot of heavy rain in the area in the days before, so the bats would not have gone out much to feed, if at all.
But they did not start coming out until nearly 9 pm, about 30 minutes after sunset. It was definitely night and dark.
The bats became very hard to see. I had to use a flash to get anything, and only when the image showed on my LCD did I really see the bats. The local folks said that a hawk had been hanging around the bridge of late and that probably caused the bats to delay emerging until it was dark.
A friend who lives in the area, Ted Keller, had suggested we check out the I-35 bridge over McNeil Rd. in Round Rock (just north of Austin). He said that bridge also had millions of bats using it as a bat “house.” We went there on Sunday night. The evening was sunny with hardly a cloud. The bats started coming out a little before official sunset and this was an amazing nature experience. My wife loves nature, but does not have the love of bats I do, but she was in awe and loved it. The bats swirled under the bridge, then came out in large groups out of the southeast end of the bridge.
The groups went into the sky and you could watch them go. The mass of bats and their group flight in the air reminded me of the starling flights going to roost in England (I have only seen videos of them). There were not many people there to watch, but they all just stood and watched with great attention as these bats came out in waves over the next half hour (they actually kept going longer, but when it was dark and getting hard to see them, the people left).
Next day, Monday, sunset came. No bats. The bats did not start coming out until nearly 9 pm, like the Congress Ave. bats. I had seen a hawk fly through the flying bats on Sunday night, and it seemed like it caught a bat, though it was hard to tell at the distance.
I get it. These little bats are very vulnerable when it is light, so they delay emergence to make it harder for hawks to get them, even though that means going out for food later (bats have a very high metabolism, especially with young to feed, so that does matter).
Still, it was fun and I learned a lot.