Larger bats with mouse ears are prey to owls, but the owls themselves probably avoid hornets for fear of being stung. New research suggests that bats take advantage of this by buzzing like hornets to keep owls at bay.
The study is led by Assoc. Prof. Danilo Rousseau from the Italian University of Naples Federico II.
A few years ago, he noticed that when he handled larger bats with mouse ears that had been caught in fog nets, those bats made a buzzing hornet-like sound. At the time, Rousseau and his colleagues were unsure of the purpose of their behavior. They wondered if this could be a method of alerting other bats in the colony, although they also suspected it might be a means of scaring off predators.
Most recently, the team tested the latest theory using 16 adult owls in captivity. They consist of eight owls and eight brown owls – four of each species have been caught in the wild, while the other four have been bred in captivity.
In the laboratory, four audio recordings were played on owls. These recordings included buzzing sounds made by larger bats with mouse ears, honey bees and hornets, along with a buzzing sound made by bats.
It has been observed that owls tend to move away from the speaker when everything from the buzzing sounds were emitted, but they came closer in the case of the non-buzzing sounds of bats. This was especially true for wildly caught owls, who would have more experience hunting bats and hornet stings.
According to Rousseau, this is the first known case of a mammal using acoustic Batesian mimicry, in which a harmless species avoids my predators, mimicking the sound of a more dangerous species.
“It is somewhat surprising that owls represent the evolutionary pressure that shapes the acoustic behavior of bats in response to the unpleasant experiences owls have with stinging insects,” he said. “This is just one of the endless examples of the beauty of evolutionary processes.”
An article about the study was recently published in the journal Current biology.