Pup Directed Vocalizations of Adult Females and Males in a Vocal Learning Bat

Abstract

Social feedback plays an important role in human language development and in the vocal ontogeny of non-human animals. A special form of vocal feedback in humans, infant-directed speech-or motherese-facilitates language learning and is socially beneficial by increasing attention and arousal in the child. It is characterized by high pitch, expanded intonation contours and slower speech tempo. Furthermore, the vocal timbre (i.e., "color" of voice) of motherese differs from the timbre of adult-directed speech. In animals, pup-directed vocalizations are very common, especially in females. But so far there is hardly any research on whether there is a similar phenomenon as motherese in animal vocalizations. The greater sac-winged bat, Saccopteryx bilineata, is a vocal production learner with a large vocal repertoire that is acquired during ontogeny. We compared acoustic features between female pup-directed and adultdirected vocalizations and demonstrated that they differed in timbre and peak frequency. Furthermore, we described pup-directed vocalizations of adult males. During the ontogenetic period when pups' isolation calls (ICs) (used to solicit maternal care) are converging toward each other to form a group signature, adult males also produce ICs. Pups' ICs are acoustically more similar to those of males from the same social group than to other males. In conclusion, our novel findings indicate that parentoffspring communication in bats is more complex and multifaceted than previously thought, with female pup-directed vocalizations reminiscent of human motherese and male pup-directed vocalizations that may facilitate the transmission of a vocal signature across generations.

The Origins of Social Knowledge in Altricial Species

“…Infant attention is captured by certain kinds of vocalizations, reinforcing altered vocal production from adults toward their offspring. For example, female greater sac-winged bats (Saccopteryx bilineata), a species with vocal production learning, direct vocalizations to their pups that have different timbre and pitch, as compared to vocalizations directed toward other adults (Fernandez & Knornschild, 2020). Zebra finches also produce pupil-directed song that results in increased juvenile attention (Chen et al 2016).…”

The soundscape of swarming: Proof of concept for a noninvasive acoustic species identification of swarming Myotis bats

“…Combining classical acoustic parameters and LFCCs can enhance the success of bat species identification in situations that have been challenging in the past and can help to make the most of acoustic monitoring. The combination of classical acoustic parameters and cepstral coefficients has led to convincing classification results for other species such as fish (Noda et al, 2016 ) and insects (Noda et al, 2019 ) and it has also been used to discriminate between individuals or contexts (giant otters: Mumm & Knörnschild, 2017 ; bats: Araya‐Salas et al, 2020 ; Fernandez & Knörnschild, 2020 ; Knörnschild et al, 2017 ). In contrast to our test data, all those studies are based on sound recordings containing vocalizations of one individual or one particular species.…”

Mothers Reveal More of Their Vocal Identity When Talking to Infants

“…The pup-directed vocalizations reported in 60 from 13 female pups -which evidently contain a high timbre variability -must be expected to result in poor classification performance and this result directly replicates findings for human speech 61 and our results from the within register tests -ADS-ADS and IDS-IDS -in which the higher variability of IDS has disadvantages over ADS recognition (see above). Hence, a lower acoustic variability in adultdirected bat vocalizations would mean that their classification rates should be higher compared to pup-directed vocalizations (classification results not reported in 60 ). Bat pups, however, are evidently good at identifying their caregivers 62 and in the light of the results reported here, it is plausible that this performance is supported by the higher variability vocalizations reported in 60 .…”

“…Hence, a lower acoustic variability in adultdirected bat vocalizations would mean that their classification rates should be higher compared to pup-directed vocalizations (classification results not reported in 60 ). Bat pups, however, are evidently good at identifying their caregivers 62 and in the light of the results reported here, it is plausible that this performance is supported by the higher variability vocalizations reported in 60 . We predict that using pup-directed bat vocalizations as training material for a recognition task would show similar training advantages to the human data reported here.…”