Bats mimic hornets when owls are around

lN THE ANIMAL kingdom, impersonators are a dime a dozen. The stick insects appear as twigs. Hawk moth caterpillars resemble venomous snakes. Edible heliconic butterflies disguise themselves with the wing patterns of noxious butterflies, and noxious ones copy each other to make it easier for predators to learn what not to eat.

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However, all of these examples are visual. Auditory mimicry is rarer. But, as he describes in current biology, Danilo Russo of the University of Naples Federico II thinks he has found a new case of it. Some bats, he thinks, mimic angry bees, wasps and hornets to scare away owls they might otherwise eat.

dr. Russo first noticed the tendency of greater mouse-eared bats to buzz a few years ago when he collected them in mist nets to study their ecology. The sound struck him as being similar to the sound of hornets in the area of ​​southern Italy where he worked. That led him to wonder if bat buzzing was a form of mimicry that helped practitioners deter would-be predators.

To test this idea, he and Leonardo Ancillotto, a colleague at Federico II, first recorded the buzz that captive bats made when grabbed. Once they had donned appropriate protective gear, they began the more perilous task of soaking up the hum, en masse, by four different species of hymenoptera: European paper wasps; buffalo-tailed bumblebees; European hornets; and domestic honeybees. Computer analysis showed that the buzzes from chiroptera and hymenoptera were indeed similar.

For the next part of their experiment, Dr. Russo and Dr. Ancillotto services 16 captive owls – eight barn and eight tawny. Both species are known to prey on bats.

The researchers placed the owls one by one in a room equipped with branches to perch on, as well as two boxes with holes in them. The boxes resembled the types of hollows in trees that owls would explore in the wild in search of food. They placed a loudspeaker next to one of the boxes and, after the birds perched, it transmitted five seconds of continuous bat buzz and a similar amount of insects buzzing three times in a row for each sound. As a control, they similarly emit various non-buzzing sounds made by bats.

During the broadcasts (which happened in random order) and five minutes later, they filmed the owls. The videos were then analyzed by an independent observer, without using their soundtracks. The results were unequivocal. Hearing both the hum of the bat and the hum of the hornet, the owls moved as far away from the speakers as they could. In contrast, when the non-humming bat sounds were played, they crept closer.

dr. Russo and Dr. Ancillotto think this is the first reported case of a mammal using acoustic mimicry to scare away a predator. However, they strongly suspect that it is not unique. Anecdotes suggest that several birds, as well as small mammals, such as dormice — particularly those that live in trees and, like dormice, in rock cavities — make buzzing sounds when their hiding places are disturbed. This has not yet been formally documented as acoustic mimicry. But given the tendency of poisonous buzzing insects to inhabit those kinds of places as well, as well as the fear these insects generate in other species, including humans, Dr. Russo that this may well be what’s going on. He therefore predicts that when these other buzzes are recorded and analyzed, the results will show that vertebrate acoustic mimicry of stinging insects is much more widespread than is now thought.

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