Atkinson, Q. D. | Search bioRxiv

bioRxiv2023

Crowdsourcing and phylogenetic modelling reveal parrot tool use is not rare

Studying the prevalence of putatively rare behaviours, such as tool use, is challenging because absence of evidence can arise either from a species inability to produce the behaviour or from insufficient research effort. Here, we tackle this challenge by combining crowdsourcing and phylogenetic modelling to approximate actual rates of a rarely observed behaviour based on limited data, targeting tool use in parrots. Crowdsourcing on a social media platform revealed novel instances of tool use in 17 parrot species, more than doubling the confirmed number of tool-using parrot species from 11 (3%) to 28 (7%). Phylogenetic modelling ranked additional species that are most likely to be unobserved tool users, suggesting that between 11% and 17% of extant parrot species may be tool users. These discoveries have implications for inferences about the evolutionary drivers and origins of tool use in parrots, revealing associations with relative brain size and feeding generalism and indicating several genera where tool use was likely an ancestral trait. Overall, our findings challenge the assumption that current sampling effort captures the full distribution of putatively rare animal behaviours. Combining our sampling and analysis methods offers a fruitful approach for investigating the distribution, drivers, and origins of other rare behaviours. This working paper has not yet been peer-reviewed.

animal behavior and cognition↗

bioRxiv2020

Acoustic regularities in infant-directed vocalizations across cultures

The forms of many species vocal signals are shaped by their functions1-15. In humans, a salient context of vocal signaling is infant care, as human infants are altricial16, 17. Humans often alter their vocalizations to produce "parentese", speech and song produced for infants that differ acoustically from ordinary speech and song18-35 in fashions that have been proposed to support parent-infant communication and infant language learning36-39; modulate infant affect33, 40-45; and/or coordinate communicative interactions with infants46-48. These theories predict a form-function link in infant-directed vocalizations, with consistent acoustic differences between infant-directed and adult-directed vocalizations across cultures. Some evidence supports this prediction23, 27, 28, 32, 49-52, but the limited generalizability of individual ethnographic reports and laboratory experiments53 and small stimulus sets54, along with intriguing reports of counterexamples55-62, leave the question open. Here, we show that people alter the acoustic forms of their vocalizations in a consistent fashion across cultures when speaking or singing to infants. We collected 1,615 recordings of infant- and adult-directed singing and speech produced by 410 people living in 21 urban, rural, and small-scale societies, and analyzed their acoustic forms. We found cross-culturally robust regularities in the acoustics of infant-directed vocalizations, such that infant-directed speech and song were reliably classified from acoustic features found across the 21 societies studied. The acoustic profiles of infant-directedness differed across language and music, but in a consistent fashion worldwide. In a secondary analysis, we studied whether listeners are sensitive to these acoustic features, playing the recordings to 51,065 people recruited online, from many countries, who guessed whether each vocalization was infant-directed. Their intuitions were largely accurate, predictable in part by acoustic features of the recordings, and robust to the effects of linguistic relatedness between vocalizer and listener. By uniting rich cross-cultural data with computational methods, we show links between the production of vocalizations and cross-species principles of bioacoustics, informing hypotheses of the psychological functions and evolution of human communication.

animal behavior and cognition↗