Some Bats Use Their Wings to Navigate in the Dark

A fruit bat from eastern Indonesia. Terry Reardon and Michael Pennay

For a while, biologist Arjan Boonman lived in Indonesia and spent much of his time traveling the country to make audio recordings of bats.

“Theres a lot of deforestation there, and lots of bats are probably going to go extinct,” says Boonman, now a postdoctoral researcher at Tel Aviv University in Israel. Fascinated by the bats, he decided to gather as much information as possible about the various species in Indonesia, before they’re gone.

One day Boonman sat down on a bus next to a friendly man, who told him he’d heard a species called cave nectar bats making a clicking sound with their wings, perhaps using it to echolocate. Echolocation is the process whereby bats and other animals bounce sound off their surroundings to help them navigate, especially in the dark. Boonman was skeptical.

Bat biologists, including Boonman, pretty much all assumed that bats only echolocate vocally, by making sounds in their larynx. It was also generally thought that the vast majority of species in this family, known as Old World fruits bats, didn’t echolocate at all, says bat expert Nancy Simmons, the curator-in-charge at the department of mammalogy at New York’s American Museum of Natural History.

However, Boonman found one record of bats making clicking sounds with their wings in the scientific literature, from 1988. But the study authors didn’t show what function the sound served, if any.

Eonycteris_withpermission A cave fruit bat. Merlin Tuttle Later, Boonman moved to Israel to continue his research and recounted the story to neuroecologist Yossi Yovel. (Neuroecology is an emerging discipline that combines neurology and ecology.)

Yovel convinced Boonman that it was a story worth looking into, and together they and a third scientist went to Thailand to record several different unrelated species of fruit bats (one of the better travel excuses out there). They found that several species of bats did indeed make clicking sounds with their wings, increasing the frequency of these clicks more than fivefold when they turned out the lights.

This and other experiments led them to conclude that the bats use these wing clicks to find their way around, and the clicking appears to function as a primitive form of echolocation, says Simmons, who wasn’t involved in the study, which was published in the journal Current Biology.

“Heres another way bats can make sounds and use information from sounds to orient themselves and find obstacles,” she says.

Macroglossus_in_exp_own_photo A megabat (Macroglossus) approaches a dish of nectar water in a lab. Arjan Boonman The technique isn’t as fine-grained as laryngeal echolocation, which the majority of bats use to find their way around and perform such impressive feats as catching tiny insects in midair in the dark, Simmons says. But it probably helps fruit bats avoid major obstacles like trees and cave walls, Yovel says.

There’s a chance that this wing clicking could have been the first step in the evolution of echolocation, Yovel says. Perhaps, for example, bats learned after a while that the sound their wings made upon flapping together could be used to gauge the distance between themselves and an obstacle. This is perhaps not as far-fetched as it sounds: You can even teach people (whose aural acuity pales in comparison with bats) a remedial form of echolocation in a short period, he says.

The scientists still don’t know exactly how the bats’ wings make the sound. It’s surprisingly difficult to pin down due to the brief nature of the sound, the speed of the bats’ wings and the fact that all of this is happening in pitch-black darkness. But it looks as if it probably happens when the wings collide, Simmons says.

To truly find out “will probably take studying these bats in complete darkness in a wind tunnel using a high-speed camera,” she adds. Perhaps somebody should get Bruce Wayne on the line.