“…and today we’re talking about a friendly sky rat. But more on that later.”
Picture a dusk-drenched desert sky where the horizon starts to move. A clear evening gives way to a tornado. But it’s not the weather, it’s a living, breathing, leathery blizzard pouring out of caverns deep within the rocky substrate. That’s right, it’s bats. Specifically, the Brazilian Free-Tailed Bats living in Southern Texas. When they get together, they really get together. It’s an airborne synchronized performance with innumerable dancers. But sticking together is one of the best ways to survive here in Life, Death, and Taxonomy.
Description
They have short, velvety fur that’s typically reddish-brown, dark brown, or grayish, sometimes with lighter patches.
The most distinctive feature is their free tail — the tail extends well beyond the uropatagium (the membrane connecting the legs and tail), often making up nearly half their total body length — which gives the species its name.
They have broad, rounded ears that are forward-pointing, wrinkled lips, long narrow wings suited for fast flight, and a somewhat flattened skull.
Measure Up
Welcome to the beloved Measure Up segment. The official listener’s favorite part of the show! The part of the show when we present the animal’s size and dimension in relatable terms through a quiz that’s fun for the whole family. It’s also the part of the show that’s introduced by you when you send in audio of yourself saying, singing, or chittering the words Measure Up into ldtaxonomy at gmail dot com.
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These bats are small, weighing about 11–15 grams (roughly the weight of a couple of quarters).
A baru nut from the Cerrado tree are protein-rich, nutrient-dense, and low calorie nuts native to Brazil. True or false–a baru nut is the same weight as a Brazilian Free-Tailed Bat.
Answer: Baru nuts are 10-20g varieties.
Wingspan of 30–35 cm (12–14 inches).
The toco toucan is Brazil’s iconic large toucan species found in the Cerrado, Pantanal, and parts of the Amazon. True or False–the toco toucan’s bill is the same length as the bat’s wingspan.
Answer: The Toco’s bill is 7–9 inches.
Fast Facts
They are native to North, Central, and South America, plus the Caribbean, ranging from the southern United States through Mexico, Central America, and into northern South America (including Brazil, which is why one common name references it).
In the U.S., they’re especially common in the southern and southwestern states, often in dry, lower-elevation areas up to around 10,000 feet in some mountains.
They roost in large colonies in caves, abandoned mines, bridges, culverts, buildings, attics, and other structures. Some massive colonies number in the millions.
Brazilian free-tailed bats are insectivores, feeding mostly on flying insects caught in mid-air using echolocation.
Their diet includes moths, beetles, flies, and ants. They forage at high altitudes and over large areas, emerging at dusk in spectacular swarms.
Are they the fastest fliers?
These bats are excellent fliers, with long, narrow wings built for speed and endurance. They may hold the record for the fastest horizontal flight speed of any mammal…
A 2016 scientific paper claimed the Brazilian free-tailed bat can reach horizontal flight speeds up to 160 km/h (about 100 mph), potentially making it the fastest animal in powered, level flight.
Researchers tracked seven bats using an airplane-based radio tracking… with a transmitter on the bat’s back and receivers on a Cessna flying overhead… they recorded most bats at ~110 km/h but one peak at 160 km/h. They also recorded another outlier at 200 km/h that discarded.
Skepticism…
Tracking positions were taken every 2–5 minutes with positional errors of 50–100 m — a big leap relative to the bat’s ~9 cm body length. Some distance estimates between points were smaller than the error margin itself, raising red flags about accuracy.
The “fastest” accolade is based in a single extreme data point: The 160 km/h came from just one instance; most speeds were lower.
For a more detailed breakdown of the study, this is a good video.
They should test it again!
Data was collected back in 2009, with transmitters ~5% of the bat’s ~12 g body weight — respectable for the era, but modern tech could improve precision.
The original study:
McCracken, G. F., Safi, K., Kunz, T. H., Dechmann, D. K. N., Swartz, S. M., & Wikelski, M. (2016). Airplane tracking documents the fastest flight speeds recorded for bats. Royal Society Open Science, 3(11), 160398. DOI: 10.1098/rsos.160398
Major Fact: Batcon: The Largest Gathering of Mammals on Earth
- Certain caves in Texas host colonies numbering in the millions—we’re talking bat metropolises, not bat Airbnbs.
- The most famous example is Bracken Cave, where upward of 15–20 million individuals roost together. That’s million with an “m”.
- Every summer evening, they spiral out of caves in a vortex formation that reduces predation risk—safety in swirling numbers.
- This mass emergence can last for hours, creating radar-visible plumes that look like storm systems.
- By gathering in colossal colonies, they maximize mating opportunities and information sharing about feeding grounds.
- The heat generated by millions of bodies helps maintain optimal temperatures for raising pups. Built-in bat HVAC.
- These bats consume hundreds of tons of insects nightly, including agricultural pests like moths and beetles—natural pest control on a biblical scale.
- Their appetite saves U.S. agriculture millions of dollars annually in crop protection and reduced pesticide use.
- The sheer density of individuals makes caves ecological powerhouses, with guano supporting entire micro-ecosystems.
- It stands as the largest known aggregation of mammals on Earth—no wildebeest migration, no caribou caravan, no human music festival comes close in raw, wriggling numbers.
Ending
So cozy up in a nice cave, cake the ground in guano, and get together in the zillions like the brazilian free-tailed bats