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Bat Field Trip

Writer's picture: Joseph ConnorsJoseph Connors

Did you know that the Mexican Free Tailed Bat (Tadarida brasiliensis) is the State Flying Mammal of Texas since 1995? They are most common bat found throughout Texas. I also recently learned that their average speed is over 60 mph and researchers measured their top speed at just below 100 miles per hour.


Bats Emerging (photo by Joseph Connors)

Not all bats live in caves. Bats also live in trees, palm trees, and man made structures. Last night we had a chapter field trip to watch the Mission Bats colony emerge at the Conway Avenue & Expressway 83 overpass. While we waited, we had a great discussion of bats and the new monitoring technology our chapter is using as part of a Texas Parks and Wildlife citizen science project. When the first plume was spotted in the distance, most figured it was a flock of birds. Soon the excitement grew as we were sure it was the bats emerging. They started flying about 8:50 pm, shortly after sunset (8:30 pm). We didn't see the huge number of bats that sometimes emerge, but I wouldn't be surprised if we saw over 1000 bats. When the groups closest to us took off, the bat detector was going crazy. A constant stream of bat calls flashed across the screen.



According to our handheld bat detector (Echo Meter from Wildlife Acoustics), I recorded possibly 8 different species during this field trip. The detector use software to compare frequencies and patterns of the bat's echolocation to suggest a species. To verify the species, the audio spectrogram need to be manually reviewed, but I haven't studied bats enough to do that. By far, the most common species call identified last night were Hoary Bats (Lasiurus cinereus). Northern Yellow Bats (Lasiurus intermedius) and Mexican Free-tailed Bats (Tadarida brasiliensis) were the next most common according to the app. The rest were represented by just a few possible recordings. Recordings taken at this location don't make the best for study because there are so many bats calling at the same time in addition to the traffic noise.


I was educated about those issues when posting some of my bat audio recordings on iNatutralist in the past. Currently there are 141 observations for bats in the RGV on iNaturalist. Only 36% of the bats observed have been verified to reach Research Grade, representing just 9 species. That includes 22 of my audio recordings. From what I have been told, we can expect around half the 32 bat species in Texas here in the Valley. Our hand held bat detector suggests I have recorded a few species that aren't known to be here. Of course, the IDs could be wrong or my list may be incomplete. Soon, the TPWD project our chapter is participating in with the professional recording equipment, software, and training will help better document what species are found here and elsewhere in Texas that haven't been studied well yet.


Looking at historical weather records for Mission, the weather on Saturday was nearly the same as our unsuccessful attempt to see the emergence last June. The high yesterday was 97 and it was around 90 at sunset with 13 mile per hour winds. I wonder what made last time different. You can read about that experience in my Batless Field Trip blog post from last year. In that post, I go into more detail on our handheld bat detector and looking at the bat spectrograms.


If you want to see what time the bats are emerging to see them yourself, check out Mission Bats on Facebook which frequently reports the times bats have been seen leaving their bridge roost near sunset. You can see a post in the group with more of Luciano's photos from our trip and a video of the detector in action.


You may also be interested in watching our meeting presentation by Anita on Gardening for Bats from last year. She talks about what you can do to improve your yard to attract nocturnal wildlife.

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