These Bats Buzz Like Hornets to Scare Off Predators

When you’re not dangerous, it can be lifesaving to pretend you’re something that is.

There’s a behavior called Batesian mimicry, where a harmless species mimics a more dangerous one in order to try to ward off predators. Some butterflies and snakes look like their poisonous counterparts so they won’t be eaten.

Researchers have just discovered the first time that mammals have used this imitation defense acoustically when they found bats making a buzzing hornet-like sound to keep owls from feasting on them.

They discovered the greater mouse-eared bat (Myotis myotis) creates a distress call that sounds like stinging bees or wasps to deter flying predators.

Study author Danilo Russo of Università degli Studi di Napoli Federico II in Portici, Italy, says he first had the idea to study mimicry about two decades ago while doing his Ph.D. work.

“I happened to mist net those bats for other reasons and noticed that when we handled the bats to take them out of the net or process them, they buzzed like wasps or hornets,” Russo tells Treehugger. “At that time, I thought it might be a way to deter predators, but then I had to wait for the right research group, including first author Leonardo Ancillotto, to test this hypothesis.”

In their work, they looked at how similar the buzzing sounds made by bats were to the stinging sounds of insects. Then they played those sounds to eight barn owls and eight tawny owls to see their reactions. They used four captive-raised owls and four wild owls of each species. They believed wild owls could be experienced with the sounds of bats and insects, while the captive owls likely have never been exposed before.

Each owl was exposed to the buzz of the bats, honeybees, hornets, and a non-buzzing bat sound, which acted as a control. Researchers recorded the bats’ behaviors before and after each sound to see how their responses changed.

The owls acted in the same way, moving farther away from the speaker when hearing the insect and bat buzzing sounds. They got closer when they heard the non-buzzing bat sounds which could signify potential prey.

They also found that the buzzes made by hornets and bats appeared the most similar when researchers excluded frequencies that owls can’t hear. So the sounds were most alike when they were heard in the ways that owls hear them.

Researchers say the results offer the first example of mimicry between mammals and insects as well as one of only a handful of examples of acoustic mimicry. The findings were published in the journal Current Biology.

Why Buzzing Helps

The bats typically make a buzzing sound when they are disturbed or handled.

“Imagine a predator seizing the bat,” Russo says. “It will get scared by the buzz for the fraction of a second the bat needs to fly away and save its life.”

Researchers aren’t sure if the owls get scared because they’ve been stung before, but that’s likely the case. They point out that birds of all types will usually avoid nest boxes or tree cavities if hornets have moved into them in an effort to stay away from potentially dangerous insects.

Researchers also aren’t sure how well the buzzing sound works in protecting the bats from predators.

“We don't know because we do not have yet any evidence from the wild, but presumably, the adaptation must work at least in some cases, which is why it was selected by natural selection,” Russo says.

Acoustic Batesian mimicry is rarer than visual Batesian mimicry like this, and this is the first time a mammal is known to imitate an insect.

“It was an exciting discovery. Here you have an evolutionary interaction involving animal species that are phylogenetically far from one another … insects, birds, and bats! Besides, it is fascinating that the similarity between the bat call and a hornet buzz only appears when frequencies not heard by owls are cut out,” Russo says.

“Those sounds are not ‘simply’ similar, they are especially so when an owl hears them. When we think of Batesian mimicry, the first thing that comes to our mind is color, but in this case, it is sound that plays a crucial role. Acoustic Batesian mimicry is way less common in nature, and I am not aware of any other mammal mimicking insect sound.”