Some bats buzz like wasps and bees when they are grabbed, and the sound seems to deter predatory owls.
The findings reveal what may be the first known case of a mammal mimicking an insectresearchers report May 9 in current biology.
From 1998 to 2001, animal ecologist Danilo Russo was conducting field studies on long-eared bats (myotis myotis) in Italy, which consisted of capturing live animals in mist nets. When he and his colleagues brought out the bats, they made a buzzing noise in the scientists’ hands that was reminiscent of wasps or bees.
“When you hear them, that’s what immediately comes to mind,” says Russo, of the University of Naples Federico II in Italy.
Years later, Russo and his team decided to test the idea that the strange buzzing was not a mere coincidence, but a type of defense mechanism called Batesian mimicry. Batesian mimics are themselves harmless, but bear a resemblance (visually, acoustically, or chemically) to a different species that is unpleasant or dangerous. When wary predators cannot distinguish harmless mimics from the noxious originals that predators typically avoid, the mimics are protected.
The researchers caught more bats and recorded their buzzing noises as they were handled. The team also recorded the buzzes of four species of stinging insects (two wasps and two bees) commonly found in European forests.
When Russo and his team compared the buzzing audio profiles of insects and bats in the lab, the researchers found that their analyzes were able to distinguish between the two sound sources most of the time.
But the audience matters. Tawny Owls (strix aluco) and owls (Tyto alba) often hunt bats, so Russo’s team wondered if the birds might be the target of the buzzing performance. When the researchers limited their sound analysis to just the frequencies heard by an owl, the buzzes became much more difficult to differentiate, particularly for comparisons involving the buzz of European hornets (crab scooter).
The team then played recordings of bat and insect buzzes, and bat social calls, to eight birds of each captive owl species at a wildlife rehabilitation center. The owls reacted to the buzzing of the insect and the bat in the same way, moving away from the speaker. Rather, they moved closer to the speaker when he played the social calls, potentially associating them with prey.
Birds tend to avoid insect bites, says Russo. “When the hornets colonize nest boxes or tree cavities, the birds don’t even try to explore them, not to mention nest there.” Russo and his team think this negative association can be evoked in nature if an owl grabs a bat and receives an indignant buzz.
This scenario may be the first known example of Batesian mimicry, acoustic or otherwise, where a mammal copies an insect, the researchers say.
In general, most examples of Batesian mimicry involve visual cues, so finding possible acoustic mimicry is exciting, says David Pfennig, an evolutionary biologist at the University of North Carolina at Chapel Hill.
Pfennig, who was not involved in the research, points to some examples of acoustic mimicry, such as burrowing owls. imitating a rattlesnake rattle or Congolese giant toads hissing like gabon vipers (serial number: 10/25/19). But these do not involve a pair of mammals and insects.
The new study makes behavioral ecologist Anastasia Dalziell think of birds other than owls. Songbirds are fairly regular acoustic mimics, says Dalziell, of the University of Wollongong in Australia, who was also not involved in the research. “I’ve been waiting for a study like this because bats are very similar, in many ways, to songbirds,” she says. “They learn their vocalizations like songbirds, at least in some cases, and can even sing, so it makes sense to me that they mimic as well.”
But behavioral ecologist Matthew Bulbert of Oxford Brookes University in England is not convinced that this is a case of mimicry. Owls encounter stinging insects and bats in totally different contexts (resting versus hunting), which makes it unlikely that the owls will be fooled, he says. Instead, the buzzing could be generally startling to an owl, increasing the chance of the bat getting loose.
“That in itself is still pretty good,” he says.