You can forget your swifts, your peregrine falcons, and your grey-headed albatrosses. They may be fast, but when it comes to level flight, it’s not a bird, but a mammal that holds the record.
Brazilian free-tailed bats (Tadarida brasiliensis) are nimble, sleight mammals, that weigh about the same as a walnut. They are known for their enormous roosts, in North, Central, South America and the Caribbean, and the dizzying spectacle they create when the females emerge at dusk. Millions of bats spiral into the darkening sky, as they head out to hunt.
It looks stunning, but for a long time, scientists underestimated bats. Bat flight was thought to be slower and less efficient than that of birds. Bats, the story goes, are less good at generating lift, and aerodynamically flawed because their sticky-out ears and weird noses (features specialized for echolocation) stymie the flow of air over their bodies.
This dogma was challenged in 2016, when a group of scientists from the US and Germany set out to measure bats on the wing. They concentrated their efforts on a 10 million-strong colony of Brazilian free-tailed bats roosting at the Frio Bat Cave in Texas.
Every night for a week at twilight, one scientist stood outside the mouth of the cave, and gently netted a single female. He then attached a tiny radio transmitter to her back and released her back into the column of emerging bats.
Twenty miles away, a second scientist was on standby in a Cessna 172 plane fitted with radio antennae. With the bat in flight, the plane took off. It then followed the bat for hours, recording data as it went.
The scientists learned many cool things. Just like birds and insects, the bats adjusted their flight speeds in response to the wind. When wind support increased, the bats flew more slowly. When there were crosswinds, they sped up. At faster speeds, bats were also more likely to pause between wing beats, suggesting they had switched to gliding.
Most impressive of all, however, were the speeds they reached. The peregrine falcon may well achieve speeds of 200 miles per hour, but it does that ‘downhill’, assisted by gravity, when it plunges from the sky. When they are flying horizontally, their maximum speed is closer to 70 miles per hour. Swifts and albatrosses can cruise at similar speeds, but Brazilian free-tailed bats leave them in the dust.
In short busts, the agile mammals can reach speeds of up to 100 miles per hour. This makes Brazilian free-tailed bats, not just the fastest flying mammal, but the fastest living, flying anything in level flight. As the scientists said themselves, when they wrote up their findings for Royal Society Open Science, the “flight performance in bats has been underappreciated.”
Top image: dizfunkshinal, CC BY 2.0 https://creativecommons.org/licenses/by/2.0, via Wikimedia Commons
