Mexican Free-Tailed Bats at Old Tunnel State Park


Over the weekend Chris and I went to the Texas Hill Country near Boerne to do some hiking and exploring of the area. We happened upon a rainy weekend, complete with some flooding in the San Antonio area. Because of this some of the areas we wanted to go to were closed. As I was planning our trip I found a small park on Google Earth called Old Tunnel State Park. So on Sunday night as we drove back from Fredericksburg to our motel in Comfort we took the Old San Antonio Road to the state park. I really wasn’t expecting a lot of people but boy, was I wrong! The place ended up being very packed by the time we were done with the bat emergence at nearly 9pm. We arrived at around 7pm and were very glad to have as it enabled us to get seating in the lower amphitheater area, thus providing us with perfect bat viewing!

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Chris and I walked down to the old tunnel, the first one in Texas, to scope out the area. We could see some bats flying around towards the back of the tunnel but none were emerging as we were over an hour early. Plus, no one is allowed that far down during the emergence—darn! We walked shortly down one of their hiking trails, but we weren’t in hiking clothes so we didn’t wander far.

A park ranger gave an excellent program discussing the local history, talking about the bats and why they have colonized the tunnel. It was interesting to hear that the pregnant mothers actually leave for a month or so to give birth in another cave. Apparently the tunnel with its two openings doesn’t allow the body heat of the bat mass to heat up the area warm enough for the bats to give birth and the pups to survive. The ranger said they needed 105* in the cave and that temperature wouldn’t be reached in the tunnel. The park and other bat researchers have tried to figure out which cave they are migrating to for birthing and they believe they’ve pinpointed a cave somewhere near Mason but aren’t for certain. Either way, the females and their pups come back about six weeks after birth to the tunnel, just about the time the males fly up from Mexico. Then, this is the peak mass of bat emergence with up to 3 million bats emerging at night!

There’s also another couple of thousand of cave myotis bats that also occupy the cave but are distinctly separate in their roosting habits. At least bats know how to share space!


Chris took this video, his is a little bit lighter than mine and he used a lens that cropped closer.


I should have upped my ISO but didn’t realize it was dark when I was looking at the screen on the camera. Anyway, this shows the bats emerging from the tunnel, rising up and then hanging a left through the trees, and then out and over the canopy. It would be really cool to see this from a mile or two down the road! When we left and proceeded to drive south we saw several bats flying low and high above the road so I think watching them from this direction would be really fun to see!

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This tiny state park is highly recommended and if you are in the area definitely stop in for the presentation and emergence! Get there at least an hour early to guarantee a seat down low. You can skip paying and stay at the very top, but Chris went up towards the end to see what he could see above the trees and the visibility was not good.

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One thought on “Mexican Free-Tailed Bats at Old Tunnel State Park

  1. Gayle Bicik says:

    Your videos are really cook – I thought it would be darker also. Cool. Glad y’all had such a good weekend.

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