Â鶹ÒùÔº

Just as human infants rely on their environment and social interactions to acquire speech, bat pups depend on their social environment for vocal learning. New research reveals that in the bat species Saccopteryx bilineata, maternal feedback influences vocal development, particularly shaping the vocalizations acquired through vocal learning. Conducted in the jungles of Panama and Costa Rica, this study offers a rare glimpse into the social factors at play in non-human mammalian vocal learning.

The work in the journal eLife.

Vocal learning is the capacity to modify existing sounds and learn new vocalizations by imitating a tutor. This ability, a form of social learning, depends on acoustic input, and—especially in social animals—some form of feedback. In humans, social feedback can positively influence language development and enhance social bonding between parent and infant.

Feedback includes vocal exchanges or showing affection, including touching or smiling at the infants as they learn to speak. Because vocal learning is rare in non-human mammals, the underlying mechanisms and key factors shaping this process are still not well understood.

The greater sac-winged bat, Saccopteryx bilineata, is a small insectivorous species inhabiting the lowlands of Central and Latin America, and one of the few mammals capable of vocal learning. During their vocal development, bat pups imitate adult males to acquire their song. The peculiarity is that this learning process is expressed in a conspicuous vocal practice behavior, called pup babbling.

Previous research has demonstrated that pup and human infant babbling share similar characteristics. On average, bat pups spend seven weeks engaging daily in long babbling bouts lasting up to 43 minutes. Adult males provide the primary acoustic input through daily singing at dusk and dawn; however, they normally do not interact with the pups. In contrast, females display various behaviors exclusively while their pup is babbling.

A team of scientists from the Museum für Naturkunde Berlin, the Humboldt-Universität zu Berlin and the Freie Universität Berlin, Ahana A. Fernandez, Nora Serve, Sarah-Cecil Fabian, and Mirjam Knörnschild, studied the vocal ontogeny and maternal feedback of wild pups in Central America over several years. The researchers observed the pups' vocal ontogeny to determine whether maternal behaviors displayed during babbling influenced aspects of vocal learning and development.

The team found that maternal behaviors significantly increased the amount of vocal practice, both daily and across the entire ontogeny.

"But what is really intriguing is that maternal behavior influences different aspects of the song syllables learned through vocal imitation," explains Fernandez. "We found that the amount and variety of song syllables is positively influenced by the mother´s behavior."

Furthermore, when mothers interact more during babbling, the pups produce more mature song syllables.

"This is fascinating because in human infants we also see the positive effect of social feedback on speech-readiness of babbling syllables," adds Knörnschild. "Seeing these parallels in another vocal learning mammal is very exciting."

This study reveals that social factors are crucial in vocal development, not only in humans but also in other mammalian vocal learners. It is an important step toward further research into the impact of social feedback on vocal learning, highlighting the importance of studying animals in their natural social environments.