Wednesday, May 9, 2012

Wednesday Search Challenge (5/9/12): Bats over Austin--where do they go?

This week I’m in Austin, Texas attending a conference on Computer-Human Interaction, a place where we speak to each other in learned tones while trying to work out where the future of computers and people will go.  

And while that’s interesting, something else has grabbed my attention this week. 

As you probably know, Austin has a remarkable bat colony that lives under one of the bridges in the middle of town.  Every evening at dusk, these bats pour out of the bridge substructure and into the sky to begin searching for insects.  They go on insect search-and-consume missions, collectively eating something like 10 tons of bugs each night.  

In talking with people at the bridge, a couple of questions kept coming up.  Can you answer these search challenges and help us understand a bit more about these bats?

1.  What kind of bats are we seeing? 
2.  What kind of bat is the most common bat in Texas? 
3.  When these bats migrate, where do they go?  (We know they go somewhere south into Mexico, but can you tell me which states they visit for the winter?) 
Searching with my echolocation…


  1. 1. Mexican free-tailed bats
    2. Same (also called Brazilian free-tailed bats)
    3. Jalisco, Sinaloa and Sonora

    About five minutes searching for "austin bats".

    1. Mexican free-tailed bat (aka Brazilian free-tail bat), Tadarida brasiliensis
    2. Mexican free-tailed bat (aka Brazilian free-tail bat), Tadarida brasiliensis
    3. Texas and Great Plains free-tailed bats migrate to Eastern and South-Central Mexico, which includes the following Mexican states: Hidalgo, Puebla, Tlaxcala, Veracruz, Morelos and México.

    Question #1: [austin texas bridge bats]

    Question #2: [most common bat in texas]
    Both pages state that Mexican free-tailed bats are the most common bat in Texas.

    Question #3: [Mexican free-tailed bats migration]
    States that Mexican free-tailed bats from Texas migrate to Eastern Mexico.

    Question #3: [where do congress avenue mexican free tailed bat go in winter?]
    States that Mexican free-tailed bats from the Great Plains typically migrate to Eastern Mexico and South-Central Mexico.

    Finally, I consulted the Wikipedia pages for "Eastern Mexico" and "South-Central Mexico" to get a list of Mexican states in those areas.

    Questions #1 & #2 were trivial; 1 minute.

    On Question #3, I found "Eastern Mexico" and "South-Central Mexico" within another 3 minutes. However, I spent an additional 10 minutes or so trying to find mentions of the specific Mexican states to which the Congress Avenue Bridge bats migrate. I finally gave up and found the states associated with the regions of Mexico previously identified.

  3. Hopefully I can answer part of it. You're most likely seeing Brazilian Free-Tailed bats. They have colonies all over Texas, with populations in the millions. My research in college was analyzing IR videos of the bats emerging from caves at dusk. Check out Dr. Kunz's work (Boston University). You'll learn all you want to know about these guys!

  4. Google Mapped "Austin Texas" and checked out the bridges in the area.

    Then searched for "bats bridge austin texas" and came up with the following:

    1. In Austin, Texas, a colony of Mexican Free-tailed Bats summers (they winter in Mexico) under the Congress Avenue Bridge ten blocks south of the state capitol. It is the largest urban colony in North America with an estimated 1,500,000 bats. (From Wikipedia)

    2. Most common bat in Texas: Mexican free-tailed bat (Tadarida brasiliensis), also known as the Brazilian free-tailed bat (also from Wikipedia and confirmed on several Texas Parks and Wildlife sites:

    3. Migration Patterns: Mexican free-tailed bats in southeastern Nevada, southwestern Utah, western Arizona and southeastern California will migrate westward and southward into southern California and Baja California, as a unit.[6] Bats in southeastern Utah, southwestern Colorado, western New Mexico and eastern Arizona migrate along the western side of the Sierra Madre Oriental into Jalisco, Sinaloa and Sonora. Some bats that summer in Kansas, Oklahoma, eastern New Mexico and Texas will migrate southward to southern Texas and into Mexico. (More Wikipedia confirmed by TPAW

  5. I believe they are Mexican free-tail bats. The colony in Austin is one of the few remaining in the US. I am not sure what states they visit in winter, though.


  7. I don't know when those bats colonized the Congress Ave. bridge, but they have been there forever. My mother, born 1926, saw them in her childhood. I recall a colony that lived in an abandoned movie theater on or about 6th Street and Congress Ave. circa 1965.

  8. All is right in wikipedia...

  9. 1.
    Congress Ave. Bridge is where a nest of Mexican Free Tailed bats are found

    2. common type of bat in Texas is the Mexican Free Tailed Bat

    Bats winter in Nueve Leon, Tamaulipas and Michoacan

  10. I'm a biologist here in Austin with the non-profit Bat Conservation, International. People look like they've gotten it mostly correct. These are Mexican/Brazilian free-tailed bats. They are migratory and do spend the winter months in Mexico. However, on a nightly basis, they leave the bridge, fly southeast, up to 60 miles in one direction, to feed over the agricultural fields. They do a number on the cotton boll worm.
    Batgirl is way off, though. There are many, many free-tailed colonies throughout the US. There's at least a dozen in the Dallas-Austin-San Antonio area.