Social calls provide novel insights into the evolution of vocal learning

Abstract

Learned song is among the best-studied models of animal communication. In oscine songbirds, where learned song is most prevalent, it is used primarily for intrasexual selection and mate attraction. Learning of a different class of vocal signals, known as contact calls, is found in a diverse array of species, where they are used to mediate social interactions among individuals. We argue that call learning provides a taxonomically rich system for studying testable hypotheses for the evolutionary origins of vocal learning. We describe and critically evaluate four nonmutually exclusive hypotheses for the origin and current function of vocal learning of calls, which propose that call learning (1) improves auditory detection and recognition, (2) signals local knowledge, (3) signals group membership, or (4) allows for the encoding of more complex social information. We propose approaches to testing these four hypotheses but emphasize that all of them share the idea that social living, not sexual selection, is a central driver of vocal learning. Finally, we identify future areas for research on call learning that could provide new perspectives on the origins and mechanisms of vocal learning in both animals and humans.

Vocal dialects in parrots: patterns and processes of cultural evolution

“…For parrots in particular, how individuals move across the landscape to exploit food resources, and the size and temporal stability of the groups formed during these movements, appears to vary greatly among species (Toft and Wright 2015). If contact calls and other vocalizations serve to mediate interactions between individuals as generally thought (Bradbury and Balsby 2016; Sewall et al 2016), then these patterns of movement likely have a strong impact on the degree of local call sharing, whether this sharing results in clinal variation or mosaic dialects, and the temporal stability of these patterns. Groups such as the Amazon parrots that exhibit a diversity of patterns of vocal variation are promising foci for tests of these hypotheses.…”

“…In contrast, most studies in parrots have focused on contact calls that are produced by both sexes and all age groups. Contact calls are thought to function to maintain social contact among specific individuals and group members within the fluid fission-fusion groups exhibited by parrots and some other taxa (Balsby et al 2012; Sewall et al 2016). What territorial song and contact calls have in common is a) that they are learned from others, and b) there may be social benefits to matching local types in order to establish territories, attract mates or gain group membership.…”

“…Note that this contrast echoes the Fisherian runaway/sexy sons versus good genes debate in general sexual selection theory. In the signalling group membership and familiarity hypothesis, the selective advantage is that individuals who converge on the local dialect will be able to integrate into social groups more readily (Sewall et al 2016). In the environmental adaptation hypothesis, a different form of selective advantage arises from adaptation of specific acoustic variants for better transmission within local environments (Handford and Lougheed 1991; Slabbekoorn 2004).…”

“…These processes are predicted to lead to the accumulation of different variants in different regions through a process that has been termed “cultural drift”, in analogy to genetic drift of genetically-transmitted traits. Importantly, cultural drift is not mutually exclusive with hypotheses inferring selective advantages; for example, dialects might originally form due to isolation and copying errors and then persist through benefits associated with sharing vocal variants with neighbours within a certain range (Sewall et al 2016). …”

Studying audience effects in animals: what we can learn from human language research

“…A similar type of accommodation may also occur when individuals signal to those with different signal sets; for example when signals are directed to an individual with a different regional dialect. Vocal dialects are found in many songbirds and parrots (see review in Sewall, Young, & Wright, 2016), as well as cetaceans (e.g. Gero, Whitehead, & Rendall, 2016; Rendell & Whitehead, 2005), and future studies could focus on whether and how individuals at the border of dialect regions may dynamically alter aspects of their signals depending on the dialect of their intended receiver.…”