Clever strategy: In order to protect themselves from hunting owls, some bats have developed an unusual defensive method. Greater mouse-eared bats imitate the menacing buzz of an angry hornet. This deters the owls because many of them have had unpleasant experiences with the insects. The defensive buzzing of bats is the first evidence of acoustic mimicry in a mammal, as researchers report in the journal Current Biology.

Mimicry is one of nature’s most fascinating phenomena. In the case of Batesian mimicry, harmless animals mimic the appearance or behavior of a defensive, poisonous, or inedible species to protect themselves from predator attacks. 

Classic examples of this are the yellow-black wasp imitation of hoverflies, a toad imitating a poisonous snake, or even a bird chick that imitates the look and behavior of a poisonous caterpillar with amazing realism.

Buzzing bats

Biologists led by Leonardo Ancillotto from the University of Naples Federico II have now uncovered an unusual case of acoustic mimicry. The impetus for this came from an observation that the scientists made when capturing greater mouse-eared bats (Myotis myotis) for experimental purposes:

“When we handled the bats to take them out of the net or process them, they invariably buzzed like wasps”, reports Ancillotto’s colleague Danilo Russo.

Such loud buzzing is a rather unusual vocalization for a bat. The biologists, therefore, took it for a stress or alarm sound that might have been intended to warn fellow species of danger – and initially ignored the sound. But the strange resemblance to the humming of a defensive insect did not let them rest. In acoustic analysis, the researchers compared the humming sounds of the bats with the humming of various insects ready to attack.

Hornet mimics deter owls

The result: the unusual sounds of the bats actually correspond well with the buzzing of a fairly defensive wasp species – the hornet (Vespra gabro). But why? What good does the greater mouse-eared bat do if it sounds like the hornet? Could it possibly be mimicry? To check this, the biologists conducted behavioral tests with the bats’ most important predators, the barn owl and the tawny owl. To do this, they played real hornet and wasp sounds, the humming of bats and neutral control tones to the birds.

In fact, the two birds of prey showed a relatively unequivocal response: “The owls responded to the buzzing of the insects and bats in a consistent manner by moving away from the loudspeaker,” report Ancillotto and his colleagues. “The buzzing triggered a clear avoidance reaction in the birds of prey.” On the other hand, when the mouse-eared bats heard the normal vocalizations, the owls approached the source of the supposed prey sounds. The buzzing of the bats, therefore, shows a clear effect on their predators.

The first evidence for acoustic mimicry in mammals

According to the biologists, their results suggest that this is a special form of Batesian mimicry: “In Batesian mimicry, a non-armed species imitates an armed one to deter predators,” explains Russo. In the case of the greater mouse-eared bat, this imitation is done acoustically – by imitating the hum of the hornet. “This makes it one of the few acoustic mimicry systems known to date,” the team says.

At the same time, this is the first documented case of acoustic mimicry in a mammal and the first evidence of mimicry in which a mammal mimics an insect. The protective strategy of the greater mouse-eared bat even extends across three major groups of the animal kingdom: the insect serves as a protective model for the mammal to deter predatory birds. “It is just one of the endless examples of the beauty of evolutionary processes!,” says Russo.

Learned from previous experiences

The unusual mimicry raises the question of how it evolved – and why owls are so fearful of hornet calls. However, the nesting behavior of the two animal groups could offer an explanation for this: Both the owls and hornets prefer to build their nests in rock crevices, tree cavities or protected cavities in buildings. As a result, it is more common for an owl to find a suitable place to sleep in a hornet’s nest.

In fact, the behavioral tests with the owls showed that the animals reacted particularly strongly to the humming sounds, which had previously had relevant experiences. Owls that had grown up in captivity, on the other hand, showed significantly weaker avoidance reactions, as the researchers report. 

Source: 10.1016/j.cub.2022.03.052 / Current Biology

Image Credit: Getty

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