To scare predators away, these bats mimic goat hamsters

Mimicry is a widespread practice among animals.

Some larvae can disguise themselves as poisonous snakes. The young of the ash aulia, an Amazon bird, may look like a poisonous larva. Syrphid flies, a species of fly, have evolved to resemble wasps, which are much more aggressive and dreaded.

All of these tricks are examples of batesim mimicry: an evolutionary trick that allows a relatively harmless animal to copy a more dangerous species to scare away potential predators.

As far as we know, this specific type of mimicry is almost forever visual in nature and is most often seen in insects, birds and reptiles.

But for the first time, a type of acoustic mimicry has recently been observed in mammals. A study published on May 9 in Current biology revealed that a common European bat species, the larger mouse-eared mouse-eared bat, appeared to mimic the sum of its horns, probably to avoid being eaten by owls.

“We found that a mammal imitated the sound of an insect to scare a bird of prey away,” says Danilo Russo, lead author of the paper and professor of ecology at the Università degli Studi di Napoli Federico II, Italy. . “This is an amazing evolutionary interaction that involves three species that are evolutionarily distant from each other.”

A SURPRISING DISCOVERY

Larger mouse-eared bats, or Myotis myotis, is a widespread European bat species that likes to feed on insects, especially beetles. They live in colonies in forests and forest edges and rest in underground caves most of the year or in buildings in the summer. These bats are often preyed upon by various birds, including barn owls (Tyto alba) and the tan owl (Strix aluco), especially when they leave or return to their sleeping place.

In 1999, Russo worked on building a library of European bat echolocation calls and collecting data on how different species communicate with each other. As he pulled a small murine out of a fog net and held it in his hands, the little animal began to shake and emit an intense and persistent buzz, says Russo, who admits to having been surprised by what he heard.

“My very first thought was … they look like chamois or wasps!”

At first, the researchers assumed that the buzz was just a common emergency call. But the sound so clearly resembled an insect that a hypothesis very quickly emerged, and years later they finally decided to check it: Could it be that these bats mimic goat hamsters or bees?

Earlier, Russo himself had collected discarded pellets of barn owls from the entrance to a cave where these bats rested. “Believe it or not, the bounce balls contained a lot of bat skulls,” he says. He therefore believed that it was not impossible that these bats “in their evolution” have ‘made’ a particularly extreme attempt to repel [les chouettes] and escape ”.

AN EXTRAORDINARY LIKE

In the current study, Russo and colleagues first compared bat hum with those from four different species of Hymenoptera, including European bees (Apis mellifera) and European goat hamsters (Vespa crabro). The team analyzed the sounds based on their wavelength, frequency, call duration and other parameters and found that their structures were very similar.

Owls hear a wider range of wavelengths than humans. By removing the louder sounds, the researchers changed the sound parameters to match what an owl would hear. They found that in the ears of these birds, the sounds of bats sounded even more like buzzing insects than on humans. “The similarity was particularly strong when variables not detected by owls … were removed,” Russo explains.

Next, the researchers played two buzzing insects using speakers. One was the buzzing sound of a bat, the other was a bat’s social appeal to captured, wild owls of two different species: barn owl and sun owl.

Although hearing bat footage caused the owls to move closer to the sound source, it mostly seemed to disturb them. They tried to escape or move away from the speaker, or at least inspect what was going on.

During the experiment, the wild owls, which may remember being bitten by flying insects, were more frightened and tried harder to escape than the captured owls. For Russo and his team, this could be explained by the fact that the captured individuals have never been in contact with a biting insect. However, at present there is little scientific data on whether owls are often stung by bees, goats and wasps, and whether they often encounter these insects.

“They probably know it’s a dangerous encounter,” Russo said. It is also for this reason that he confirms that this type of Batesian mimicry is undoubtedly a technique used by bats when they have been captured and want to buy time to be able to escape.

FUTURE RESEARCH

As is always the case with such findings, many questions remain.

Future work will have to replicate these findings in nature rather than in the laboratory and with a larger number of owls to confirm whether this is really a form of batesic mimicry, says Bruce Anderson, professor of entomology at the University of Stellenbosch, South Africa, who were not involved in the investigation. Also, check to see if owls are simply startled by the amount of bats buzzing, as they can be blown away by any other sudden loud noise. “We could investigate whether this is a case of mimicry or exploitation of a sensory bias,” Anderson says.

It remains unclear whether and to what extent owls fear buzzing insects, although the data seem to indicate that birds generally avoid nesting in cavities occupied by such insects. Researchers could also learn more about these buzzers and find out if they are unique to biting insects, or if other insects can produce them as well. It would also be interesting to see if owls that have been stung in the past react more fearfully than those that have not, according to David Pfennig, a professor of biology at the University of North Carolina at Chapel Hill who did not attend. examination.

Although facial expressions are common, and some cases of batesic facial expressions are well known, much of the phenomenon remains mysterious and startling, Pfennig adds. For him, that is why such discoveries are important. “Batesian mimicry provides some of our best examples of how natural selection can enable remarkable adaptation, including between groups of organisms that are very distant from each other,” he explains. There are other examples of acoustic mimicry between different species: for example, the burrowing owl emits hisses similar to those of rattlesnakes, but what appears to be the first is a mammal copying an insect.

In the future, researchers would like to refine and expand their research.

“While it is always helpful to validate observations in the field, our results were crystal clear,” Russo says. “It would be interesting to observe similar strategies in other species. With more than 1,400 species of bats, plus a handful of non-bat vertebrate species that also buzz when disturbed, Russo believes that species other than the one they studied could use the same trick.

According to Anastasia Helen Dalziell, an ornithology researcher at the University of Wollongong, Australia, who was not involved in the study, this strategy of cavity-living animals mimicking scary sounds to avoid predators could actually be widespread.

“Most of our knowledge of facial expressions has been gained through studies of visual facial expressions, but in principle, facial expressions could work for anyone. [type] meaningful, ”says Dalziell. “It’s really great to have another example of acoustic mimicry … to help encourage a broader study of mimicry.”

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