Bat-esian mimicry: bats buzz like hornets to dissuade predators

Some organisms have evolved to mimic more dangerous things so that predators will avoid them: harmless snakes display venomous snakes’ colour patterns, and some flies look like bees.

This trick is called Batesian mimicry – and while most of the examples we know about are visual, it can be done with sound, scent, and other senses as well.

An international team of researchers has found a rare case of sound-based mimicry in bats. The bats buzz like hornets to drive away predatory owls. Bat-esian mimicry, if you will.

According to the researchers, who have described their findings in a paper in Current Biology, it’s the first-known example of acoustic mimicry in a mammal. It’s also the first time a mammal has been found to be imitating an insect.

The research centres around the greater mouse-eared bat (Myotis myotis), which is native to much of southern Europe and the Middle East – from Portugal, all the way to Turkey and Israel. These bats are predated on by a variety of owls.

Co-author Danilo Russo, a researcher at Università degli Studi di Napoli Federico II, Italy, says that years ago he noticed the bats’ mimicry while he was conducting field research using mist nets.

“When we handled the bats to take them out of the net or process them, they invariably buzzed like wasps,” says Russo.

The researchers thought it was a strange distress call and have only recently decided to investigate it properly.

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First, they compared sound recordings of the bats to recordings of four local wasps, bees and hornets (hymenopteran insects), and found several similarities. These similarities became more pronounced when the researchers considered sounds that are only detected in owls’ hearing ranges.

Then, they played the bat buzzes to 16 captive owls (eight barn owls and eight tawny owls) in turn, to see what they would do. Eight of the owls – four from each species – had been bred in captivity, while the other half were wild animals, and thus probably had “experience” of hymenopterans.

Each owl behaved differently, but they all consistently moved away from the speaker emitting the bat noises, and experienced owls moved slightly further. Conversely, when played a control noise that didn’t mimic hymenopterans, the owls approached the speaker to investigate it.

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Russo says that while they don’t have the data to prove that stinging insects attack owls, it’s likely they do. In general, he adds, birds avoid nesting in trees that are already occupied by bees, wasps or hornets.

In their paper, the researchers also point out that other bat species buzz too, so this might not be a unique tactic.

“It is somewhat surprising that owls represent the evolutionary pressure shaping acoustic behaviour in bats in response to unpleasant experiences owls have with stinging insects,” says Russo.

“It is just one of the endless examples of the beauty of evolutionary processes!”