Vocal Signature in Wild Infant Chimpanzees

Abstract

A large array of communication signals supports the fission/fusion social organization in chimpanzees, and among them the acoustic channel plays a large part because of their forest habitat. Adult vocalizations convey social and ecological information to their recipients allowing them to obtain cues about an ongoing event from calls only. In contrast to adult vocalizations, information encoded in infant calls had been hardly investigated. Studies mainly focused on vocal development. The present article aims at assessing the acoustic cues that support individual identity coding in infant chimpanzees. By analyzing recordings performed in the wild from seven 3-year-old infant chimpanzees, we showed that their calls support a well-defined individual vocal signature relying on spectral cues. To assess the reliability of the signature across the calls of an individual, we defined two subsets of recordings on the basis of the characteristics of the frequency modulation (whimpers and screams) and showed that both call types present a reliable vocal signature. Early vocal signature may allow the mother and other individuals in the group to identify the infant caller when visual contact is broken. Chimpanzee mothers may have developed abilities to cope with changing vocal signatures while their infant, still vulnerable, gains in independence in close habitat.

Individuality in coo calls of adult male golden snub-nosed monkeys (Rhinopithecus roxellana) living in a multilevel society

“…This result supports the notion that subtle combinations of different acoustic features make up the call characteristics of an individual caller (Epsmark 1975). Similar findings that multiple parameters complementarily contribute to vocal individuality have also been reported in several other mammals and birds ( Papio hamadryas ursinus : Rendall 2003; Presbytis thomasi : Wich et al 2003; Dama dama : Vannoni and McElligott 2007; Pan troglodytes : Levréro and Mathevon 2013; Spheniscus demersus : Favaro et al 2015; Bos taurus : Torre et al 2015). …”

“…Individual distinctiveness in acoustic features of the same call type has also been reported in many species of social animals (e.g., Spheniscus demersus : Favaro et al 2015; Pan troglodytes : Levréro and Mathevon 2013; Papio hamadryas ursinus : Rendall 2003; Dama dama : Vannoni and McElligott 2007). Vocal individuality provides a crucial prerequisite for individual recognition (Pollard and Blumstein 2012; Tibbetts and Dale 2007).…”

Individual Distinctiveness in Call Types of Wild Western Female Gorillas

“…PIC is calculated as CV inter /CV intra . We consider PIC value of greater than 1 as signifying that the parameter is distinct among individuals and can thus be used for individual recognition, as in previous studies (e.g., [1], [52], [53], [56]). We tested whether calls differed in their PIC values using the Friedman test.…”

“…We then used linear mixed modeling (LMM) [79] to test whether distinctiveness of call parameters (those which correlated >0.45 with the functions generated by DFA) was significant after controlling for unequal samples and after adjusting for multiple analyses using Hochberg's correction [80]. Additionally, in order to obtain the statistical significance (equivalent to p-value) of the mean effect size [56], [77], we ran permutated DFAs (fitting and validation) using a function written by Roger Mundry in R (version 3.0.1; R Core Team 2013), which is based on the function lda of the R package MASS [78]. This procedure, including 100 random selections and 1000 iterations, allows associating p-values to the observed correct classification rates of both the normal and cross-validated DFAs, given enough cases per individuals.…”

“…Although systematic study of individual distinctiveness and acoustic variability across the species' complete vocal repertoire is needed to understand the adaptive functions they play in the animal's communication systems, few attempts have been made thus far (skuas: [51]; primates: [12], [52], [53]). Instead, the majority of studies have focused on the analysis of only one vocalization at a time (e.g., [14], [15], [54]) or at maximum two (e.g., chimpanzees: [55], [56]; baboons: [50], [57]; putty-nosed monkeys: [58]). …”