IN THE ANIMAL kingdom, copycats are a dime a dozen. Stick insects pretend to be twigs. Hawk moth caterpillars resemble venomous snakes. Edible Heliconid butterflies disguise themselves in the wing patterns of noxious ones, and the noxious ones copy each other to make it easier for predators to learn what not to eat.
However, all of these examples are visual. Auditory mimicry is rarer. But, as described in current biology, Danilo Russo of the University of Naples Federico II believes he has found a novel case. He believes that some bats mimic angry bees, wasps and hornets to ward off owls that might otherwise eat them.
Dr. Russo first noticed the propensity of great long-eared bats to buzz a few years ago, when he was collecting them in mist nets to study their ecology. The noise sounded similar to the sound of the hornets that inhabited the area of southern Italy where he was working. That led him to wonder if the bats’ buzzing was a form of mimicry that helped its practitioners scare away would-be predators.
To test this idea, he and Leonardo Ancilotto, a colleague of Frederick II, first recorded the buzzing noise captured bats made when they were handled. Then, having put on suitable protective clothing, they embarked on the more dangerous task of recording the buzz produced, mass, by four different species of Hymenoptera: European paper wasps; buff-tailed bumblebees; European hornets; and domestic bees. Computer analysis revealed that the buzzes of Chiroptera and Hymenoptera were, in fact, similar.
For the next part of their experiment, Dr. Russo and Dr. Ancilotto hired the services of 16 captive owls: eight barn and eight tawny. Both species are known to hunt bats.
The researchers put the owls, one at a time, in an enclosure equipped with branches for them to perch on, and also two boxes with holes in them. The boxes resembled the kind of tree cavities that owls would explore in the wild for food. They placed a loudspeaker next to one of the boxes, and after the birds settled in, they broadcast through it five uninterrupted seconds of bat buzzes and a similar number of insect buzzes three times in succession for each noise. As a control, they similarly emit various sounds that are not buzzing sounds made by bats.
During the broadcasts (which occurred in random order) and for five minutes afterward, they videotaped the owls. The videos were then analyzed by an independent observer, without the benefit of their soundtracks. The results were unequivocal. When they heard the buzzing of the bats and the buzzing of the hornets, the owls moved as far away from the speakers as they could. On the contrary, when the sounds of non-buzzing bats were played, they sneaked up.
Dr. Russo and Dr. Ancilotto believe this is the first reported case of a mammal using acoustic mimicry to scare off a predator. They strongly suspect, however, that it is not unique. Anecdotes suggest that various birds and also small mammals, such as dormouses, particularly those species that dwell in trees and, like dormouses, in rock cavities, buzz when their hiding places are disturbed. This has not yet been formally documented as acoustic mimicry. But given the propensity of venomous buzzing bugs to inhabit such places as well, and also the fear these bugs cause in other species, including humans, Dr. Russo thinks this may well be what’s happening. . Therefore, he predicts that when these other hums are recorded and analyzed, the results will show that acoustic mimicry of stinging insects by vertebrates is much more widespread than currently believed. ■
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