ABOVE: Greater mouse-eared bats
STEFAN GREIF
EDITOR’S CHOICE IN ECOLOGY & ENVIRONMENT
The paper
L. Stidsholt et al., “Hunting bats adjust their echolocation to receive weak prey echoes for clutter reduction,” Sci Adv, 10:eabf1367, 2021.
Most of what is known about bat echolocation has been learned under controlled laboratory conditions or in the wild with stationary microphones. While these setups have revealed that bat calls and flight trajectories change during hunting sessions, they are less than ideal for understanding the complex dynamics of how bats “see” their environments through the echoes of those calls.
“It’s so hard to study, especially in the wild, because how do we record how animals perceive the world?” says Laura Stidsholt of Aarhus University in Denmark. To get a better understanding of bat echolocation, Stidsholt and other researchers traveled to the Orlova Chuka cave in Bulgaria, where a colony of greater mouse-eared bats (Myotis myotis) live. There the researchers captured 10 females and affixed a small pack to each of their backs that carried sensors to pick up on the bats’ motion, calls, and echoes.
The bats were released about 8 kilometers away from the hunting ground, which allowed the team to get a baseline for what it sounds like when the animals are simply flying from place to place. After recovering the packs, the researchers used acceleration data and auditory recordings to associate various calls with certain activities. They identified sounds made during active hunts by the crunching noise that routinely followed.
Bats use louder calls while in transit than at other times, the team found, resulting in more returned echoes that give the bats a broad picture of the world around them. As the animals narrow in on prey, their sounds become much weaker. The researchers hypothesize that with this change, bats are only receiving echoes from the immediate environment of the prey they’re pursuing.
Among the limitations of the study, Stidsholt says, is the small sample size and the fact that recordings were only taken for one night on each bat. The recording length was dictated by the size of the battery.
The ability of the sensors to pick up on not just the bat’s call but the echo as well “provides much-improved access to the minutiae of how bats interact with their prey and surroundings in the wild, and brings the sensory perspective from bystander much closer to that of the main character, the echolocating bat,” says Signe Brinkløv, a bat biologist at the University of Southern Denmark who was not involved with the work. She notes that while the bats in the study were insectivores, it would be interesting to find out how carnivorous or fruit-eating species deploy their calls when homing in on food. “More studies like this will certainly help enlighten how and why echolocating bats use different foraging strategies.”
