To scare off potential predators, some animals display the traits of more deadly creatures. A scarlet kingsnake, for example, wears a red, black and yellow striped pattern similar to that of a venomous coral snake; innocuous butterfly species display the same beautiful splashes of color on their wings as their noxious relatives; and nestlings of Amazonian bird species are thought to avoid predation by exhibiting movement and bright orange hue of a toxic caterpillar.
These evolutionary adaptations are examples of Batesian mimicry – named after the 19th-century British naturalist Henry Walter Bates – when harmless species evade predators by mimicking more dangerous species that their hungry foes know to avoid.
Most instances of Batesian mimicry that have been discovered are visual. In comparison, there are few examples of mimicry with sound. “Acoustic mimicry is very rarely documented in nature,” said Leonardo Ancillotto, an ecologist at the University of Naples Federico II.
Dr. Ancillotto and colleagues have discovered not only a new case of acoustic Batesian mimicry, but also the first documented between mammals and insects. In their work, published Monday in the journal Current Biology, they report a species of bat that mimics the buzzing sound of stinging insects like hornets to deceive owls that might otherwise eat them.
Bats are well-known for using echolocation to maneuver through the air and locate their prey, but they also use various social calls to communicate with one another.
“We know that sound is very important for bats,” said Gloriana Chaverri, a behavioral ecologist at the University of Costa Rica and an author of the study.
Even knowing this, Dr. Chaverri was fascinated by the acoustic mimicry finding. “This is something really new – they’re using the sound to confuse, to deceive predators,” she said.
It was around two decades ago that the idea for this research first came about. Danilo Russo, a study co-author and now an ecologist at the University of Naples Federico II, was a graduate student working to create a database for all Italian bat species’ echolocation calls. When handling one species in the field, greater mouse-eared bats, he was struck by their intense buzzing. But he had to wait years until he was able to test the hypothesis that they did this to deter predators.
To test if these buzzing bats do in fact mimic buzzing insects to evade predators, the researchers focused on hornets, bees and two owl species common to the bat’s geographic range. Wild owls likely to have come across a stinging insect before and owls raised in captivity were both included in the study.
The researchers collected data on how the owls behaved while audio of a variety of sounds were played over a speaker. The owls generally moved away from the speaker when they heard any buzzing, and approached it in response to a non-buzzing bat’s social call. But the response of wild owls was far more pronounced than the response of owls raised in captivity, supporting the researchers’ hypothesis that the greater mouse-eared bat adapted to evade predators by mimicking the sound of stinging insects that their predators knew to avoid.
The researchers also discovered after analysis of the audio that the owls, because of their hearing range, would find the bats and hornets particularly similar sounding.
David Pfennig, an evolutionary biologist at the University of North Carolina, Chapel Hill, who was not part of the study, is intrigued by the possibility of an adaptation that involves species that diverged from their last common ancestor hundreds of millions of years ago.
“Mimicry is just such a powerful idea in science and evolutionary biology in particular,” he said. “It shows how you can get remarkable adaptations even among really distantly related groups.”
Sean Mullen, an evolutionary biologist at Boston University also not involved in the research, noted the potential limitations of the work, including the small number of owls used, and said he would be curious to see if – on a larger scale – the data supported the hypothesis.
But he was enthusiastic to learn more.
“Any time we can find examples where evolution may have led to adaptation it’s more evidence for how amazing life is,” he said.