Bats buzz like hornets to scare off owl predators

A greater mouse-eared Bat flying at night

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

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

Many animals copy other creatures in a bid to make themselves seem less palatable to predators. Most of these imitations are visual. North America’s non-venomous scarlet kingsnake (Lampropeltis elapsoides), for instance, has evolved to have similar colour-coding to the decidedly more dangerous eastern coral snake (Micrurus fulvius).

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

“When we think of mimicry, the first thing that comes to mind is colour, but in this case, it is sound that plays a crucial role,” he adds. The research was published on 9 May in Current Biologyone.

Bee-like buzzing

Because they are nocturnal and have poor eyesight, most bats rely on echolocation to find their way around, and communicate using a wide array of other noises. Russo first noticed that the distress call of the greater mouse-eared bat sounded like the buzzing of bees or hornets while he was catching the bats for a different research project.

To investigate whether other animals might make the same connection, Russo and his colleagues compared the sound structure of buzzing by the European hornet (Vespa crabro) to that of the bat’s distress call. At most frequencies, the two sounds were not dramatically similar, but they were when the bat’s call was stripped down to include only frequencies that owls — one of the animal’s main predators — are able to hear. This suggests that the distress call as heard by owls strongly resembles the buzzing 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 speakers when playing recordings of social bat calls, as if looking for prey. But a recording of hornets buzzing usually caused owls to distance themselves from the speakers.

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

Wasps and other stinging insects have common warning signs — such as black and yellow stripes — that other animals have been known to imitate trick predators into leaving them alone. But warning coloration is less obvious at night. “It makes total sense to me that bats, with their remarkable vocal abilities, would resort to acoustic means to fool predators,” says Mirjam Knörnschild, an animal-behaviour ecologist at the Museum for Natural History in Berlin.

Owls avoid hornets in the wild, says Johanna Mappes, an evolutionary ecologist at the University of Helsinki, so it isn’t surprising that they would be wary of anything that reminded them of the insects’ buzzing.

Russo says that this research could help scientists to spot other sound-based mimicry that might have so far flown under the radar.

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