77: Brazilian Free-Tailed Bat (aka the Mexican Free-Tailed Bat)

I write to you from Arapahoe, Ute, and Cheyenne land. I am interested in learning about the different animals that live in the place where I was born. Before we start with today’s animal, I want to emphasize that biological classification as understood by western society has its roots in racism, sexism, and transphobia – here’s a good explainer about why.

If I asked you who one of the most abundant mammals in North America was, would you guess a bat? I mean right now you probably would because you are reading a newsletter whose title involves a bat, specifically the Brazilian Free-Tailed Bat (aka the Mexican Free-Tailed Bat) (Tadarida brasiliensis). But still. There are millions of bats within each colony of bats – one in Texas is estimated to have 20,000,000 members! Compare that to, say, wolves – there are around 200,000 to 250,000 wolves on earth. How about a more abundant species – deer – scientists estimate there are around 30,000,000 white tailed deer in the world. So – that’s a lot of bats!*

Way back in newsletter #30, we discussed the Big Free-Tailed Bat, and I noted that free-tailed bats are some of the speediest animals on earth. The Brazilian Free-Tailed Bat may very well be the fastest horizontal mover of any animal, reaching speeds of up to 100 mph (though measuring this is difficult and has not been independently verified). Personally I would not mind sitting outside a bat colony with a radar gun. Perhaps I could sit by the Orient Mine of the San Luis Valley in south central Colorado, where a colony of more than 100,000 of these bats started living around 1900. The Brazilian Free-Tailed Bat is very good at moving into manmade spaces, with a special preference for mines. Luckily for them, lots of miners spent the late 1800s and early 1900s digging up every part of Colorado that they even dreamed might have precious resources to be extracted.

The Orient Mine colony is the largest bachelor colony that we know of – those large roosts I mentioned above are largely occupied by female bats and their young. Male bats occupy it and other parts of southern Colorado during the summer; in the winter, they migrate along with female bats of their species south to Mexico and Central America. This is a pretty great video to learn more about the Orient Mine colony. I particularly love the caption, “Colorado is home to Brazilian Free-Tailed Bats. WE love our bats and do everything we can to take care of them.”

A few other quick Brazilian free-tailed bat facts:

-          The Colorado colonies consume literal tons of insects, with the bats hunting at night, sometimes flying as far as 40 miles away from their roosts to forage.

-          They have a special Z-shaped molar specifically used for grinding insects.

-          These bats seem to prefer human structures for their roosts!

-          From Wikipedia: “On 6 November 2014, Aaron Corcoran, a biologist at Wake Forest University, North Carolina, reported online in Science that his team and he had detected Mexican free-tailed bats emitting ultrasonic vocalizations that had the effect of jamming the echolocation calls of a rival bat species hunting moths. The ‘jamming’ call led to an increased chance of the rival missing its prey, which the Mexican free-tailed bat was then able to eat itself.”

*As for most abundant winged vertebrate, well, there’s chickens. Somewhere around 30-60 BILLION chickens. Trying to visualize the quantity of chickens on earth freaks me out.