The mothers even appeared to recognize their offspring's cries as adults. Credit: Gunter Marx Photography via Getty Images

A single bat colony contains hundreds or even thousands of the winged mammals . But with less-than-ideal eyesight and so many neighbors, how do mothers identify their pups amid the extremely crowded conditions? Writing in a new study published today in the journal Frontiers in Ethology , researchers say it often comes down to the subtle, unique vocalizations emitted by their individual offspring. To assess their responses, the team relied on an even more delicate biological signal—the mother bat ’s own heartbeat.

The investigation began when biologists at Japan’s Doshisha University noticed a surprising—but consistent—behavior among the Japanese house bats ( Alionoctula abramus ) in their laboratory colony. Whenever a pup wandered too far from its roosting area, only its mother raced to the rescue.

“We knew that pups emit isolation calls—acoustic distress signals—when separated.…