Bats buzz like hornets to scare off owl predators

To owls, the greater mouse-eared bat’s distress call sounds like the buzzing of hornets.Credit: F. Deschandol and P. Sabine/Biosphoto/Minden Pictures

Some bats can mimic the sound of buzzing hornets to scare owls away, researchers say. The discovery is the first documented case of a mammal mimicking an insect to deter predators.

Many animals copy other creatures in an effort to make themselves less palatable to predators. Most of these imitations are visual. Non-venomous North American Scarlet Queensnake (Lampropeltis elapsoides), for example, has evolved to be color-coded similar to the decidedly more dangerous eastern coral snake (Micrurus fulvius).

Now, a study comparing the behavior of owls exposed to insect and bat sounds suggests that greater mouse-eared bats (myotis myotis) may be among the few animals to have weaponized the sound of another species, says co-author Danilo Russo, animal ecologist at the University of Naples Federico II in Italy.

“When you think of mimicry, the first thing that comes to mind is color, but in this case it’s sound that plays a crucial role,” he adds. The research was published May 9 in Current biology1.

buzzing bee

Because they are nocturnal and have poor eyesight, most bats rely on echolocation to locate themselves and communicate using a wide range of other noises. Russo first noticed that the greater mouse-eared bat’s distress call sounded like the buzzing of bees or hornets as he caught the bats for a different research project.

To determine if other animals might make the same connection, Russo and his colleagues compared the sound structure of the European hornet’s buzz (Vespa crabro) to that of the bat’s distress call. At most frequencies the two sounds were not radically similar, but they were when the bat’s call was reduced to include only frequencies that owls – one of the top predators of the animal – are able to hear. This suggests that the distress call heard by owls strongly resembles the hum of a hornet, Russo says, so it could fool predators.

To test this idea, the researchers played bat and insect noises to owls living in captivity. They found that the birds tended to approach the loudspeakers when playing recordings of bat social calls, as if looking for prey. But a recording of buzzing hornets usually caused the owls to wander away from the speakers.

Many owls also moved away from the speakers when they heard the bats’ distress call. This supports the idea that the buzzing of bats could confuse owls into thinking a hornet is nearby, Russo says.

Wasps and other stinging insects have common warning signs – such as black and yellow stripes – that other animals are known to mimic to trick predators into leaving them alone. But the warning coloration is less obvious at night. “It makes perfect sense to me that bats, with their remarkable vocal abilities, use acoustic means to deceive predators,” says Mirjam Knörnschild, animal behavior ecologist at the Berlin Museum of Natural History.

Owls avoid hornets in the wild, says Johanna Mappes, an evolutionary ecologist at the University of Helsinki, so it’s no surprise that they distrust anything that reminds them of the buzzing of insects.

Russo says this research could help scientists spot other sound mimics that may have so far gone under the radar.

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