A mother-pup pair of greater sac-winged bats. Image credit: Michael Stifter (CC BY 4.0)
Babies learn to speak by imitating the sounds made by those around them. This process is shaped not only by their passive exposure to language, but also by the smiles, gestures and other forms of encouragement displayed by their caregivers.
The impact of this social feedback has been extensively researched in people, yet it is still poorly understood in the rare non-human species that also learn their vocalizations by imitating adults. Most studies in such animals have focused on interactions between a single tutor and tutee in captivity, failing to acknowledge the influence of other individuals in the wild.
Found in the rainforests of Central and South America, greater sac-winged bats provide a unique opportunity to explore the social mechanisms of vocal learning. Much like human babies, their pups babble; they spent nearly a third of their daytime activity vocalizing and practising the songs they hear from adult males. However, it is with their mothers that these pups most frequently interact.
To investigate whether maternal feedback influences vocal learning, Fernandez et al. followed nineteen greater sac-winged pups from wild colonies in Panama and Costa Rica over two breeding seasons. They focused on three vocal learning measures: how long pups practiced babbling for, the number and diversity of song syllables they produced, and how ‘mature’ these were compared to those of adult males. The team also tracked how often mothers interacted with their respective babies (by hovering overhead or touching them, for example), as well as the number of adult males in the vicinity.
Statistical analyses showed that pups with more involved mothers babbled longer each day, and for more days overall; they also produced a wider variety of adult-like sounds, and a higher percentage of syllables that sounded like those produced by an adult singer. In contrast, the number of singing males nearby did not improve any measure of vocal learning. By shedding light on how social feedback influences song acquisition in non-human species, the findings by Fernandez et al. help to better understand the factors that shape vocal learning, and the evolution of language.
