Like people, baby Egyptian fruit bats mimic the noises and chatter their mothers and other adults make, according to a new study published in Science Advances this week.
The chicks of parrots and songbirds, as well as human babies, can all learn vocally -- a phenomenon that’s only been documented in a few animals so far. Vocal learning is crucial for the development of speech in people, yet most studies on vocal learning have been conducted in birds. A mammalian model could really help us understand how we evolved our capacity for language.
So, a Tel Aviv University trio led by Yossi Yovel turned to Egyptian fruit bats (Rousettus aegyptiacus), extremely social mammals who live in large, cozy roosts within caves. These bats can live up to 25 years, and they communicate with each other using a rich repertoire of sounds. Here’s an Egyptian fruit bat mother leaving the cave with her young pup:
The team raised five fruit bat pups in an isolated chamber so they couldn’t hear any adult vocalization. They had their mothers, but in the absence of other adults, she typically remained silent. A separate (control) group of five pups were raised with their mother and one male; these pups were exposed to intense chatter. The researchers continuously monitored both groups using video and audio recordings over several months.
After analyzing over a million vocalizations, the researchers noticed that, over time, the pups raised with their mothers and another adult started making more specific calls that sounded a lot like those mom would make. The communication abilities of the acoustically-isolated pups, on the other hand, lagged behind. Over several weeks and months, those babies continued to make infantile, “underdeveloped vocalizations,” like isolation calls when they were worried that they’d been left alone in the roost. (They also made babbling sounds, Science explains.) But they didn’t display any behavioral differences, which means means that vocal -- and not social -- deprivation delayed their ability to communicate.
Five months in, the team mixed the isolated and non-isolated pups. The babbling baby bats caught up and closed the vocal gap quickly. A month later, they sounded just like the control bats and adult bats. Songbirds have a short, critical period for vocal learning, and that's absent here -- which makes bat learning delightfully human-like.
Furthermore, in playback experiments using recorded bat calls, isolated pups mimicked what they heard. Exposure to adult vocalizations, the team concludes, is both necessary and sufficient to induce vocal learning in these bats. Figuring out what’s going on in these bat brains could help us understand the evolutionary basis of language acquisition in people.
Images: Daniel Berkowic (top), Jens Rydell (middle, bottom)