Vocal Complexity

Social and vocal complexity in Emballonurid bats
According to the Machiavellian intelligence hypothesis (or ‘social brain hypothesis’, Dunbar 1998), the driving force in the evolution of primate intelligence is social expertise, which enables the manipulation of and cooperation with other social group members (Whiten & Byrne 1988, Whiten 1999). Social interactions require communication and interspecific differences in social complexity may explain the observed variation of vocal repertoire complexity in different species (Dunbar 2003, Pinker 2003). While this proposition apparently applies to primates (McComb & Semple 2005), marmots (Blumstein & Armitage 1997), herpestids (Le Roux et al. 2009) and certain birds (Poecile; Freeberg 2006), little evidence has been found so far in bats (reviewed in Wilkinson 2003). This could be due to the lack of comparative studies incorporating both behavioral observations on indicators of social complexity (e.g., behavioral repertoire size, group size, composition, and stability) and genetic analyses to assess the impact of sexual selection on social complexity and, accordingly, vocal complexity.

We are testing the influence of social complexity on vocal complexity in six sympatric species of Emballonurids (Saccopteryx bilineata, Saccopteryx leptura, Rhynchonycteris naso, Balantiopteryx plicata, Cormura brevirostris, and Peropteryx kappleri). Our study will use a comparative approach to investigate vocal complexity and social complexity and test the following predictions:

(1) Vocal complexity is dependent on the respective mating system type, with polygyny requiring a bigger vocal repertoire than monogamy.
(2) Mechanisms to acquire vocal repertoires are dependent on vocal repertoire size, with vocal learning occurring only in species with large vocal repertoires.

Dunbar. 1998. Evol Anthropol 6:178–190

Dunbar. 2003. Ann Rev Anthropol 32:163–181

Freeberg. 2006. Psychol Sci 17:557-561

McComb & Semple. 2005. Biol Lett 1:381-385

LeRoux et al. 2009. Naturwissenschaften 96:575–584

Pinker. 2003. Language evolution, pp. 16–37. Oxford University Press

Whiten & Byrne. 1988. Machiavellian Intelligence. Oxford University Press

Whiten. 1999. MIT Encyclopedia of the Cognitive Sciences, pp. 495-7. MIT Press

Wilkinson. 2003. Animal Social Complexity, pp. 322-341. Harvard University Press