Learned vocal group signatures in the polygynous bat Saccopteryx bilineata Mirjam Knörnschild a, * , Martina Nagy b , Markus Metz a , Frieder Mayer b , Otto von Helversen c a Institute for Experimental Ecology, University of Ulm, Ulm, Germany b Museum für Naturkunde, Leibniz-Institut für Evolutions- und Biodiversitätsforschung, Berlin, Germany c Institute for Zoology, University of Erlangen-Nuremberg, Erlangen, Germany article info Article history: Received 21 March 2012 Initial acceptance 13 April 2012 Final acceptance 18 June 2012 Available online xxx MS. number: 12-00230R Keywords: call convergence greater sac-winged bat horizontal learning peer influence Saccopteryx bilineata vocal learning Vocal group signatures facilitate group cohesion or the exclusion of nongroup members and thus greatly affect the social system of any given species. This is especially significant for highly mobile animals such as bats. The greater sac-winged bat, Saccopteryx bilineata, lives in a harem-based resource defence polygyny with patrilineal kin groups and female-biased natal dispersal. Pups of both sexes produce isolation calls to elicit maternal care. We analysed isolation calls from 25 pups born in seven different social groups in search of vocal signatures. In addition to a constant individual signature, isolation calls exhibited a group signature that became more prominent during ontogeny. Call convergence of fellow pups was independent of relatedness among pups and not driven by maturation effects, showing that the group signature was acquired through social modification, a form of vocal production learning. Behav- ioural observations of free-living bats indicated that isolation calls were used by adult males to appease more dominant males and to court unfamiliar females. The learned group signature in isolation calls may function as a ‘password’ that reliably associates individuals with their natal colony. This, in turn, could facilitate male harem acquisition and female inbreeding avoidance in the polygynous S. bilineata. The flexibility inherent in the vocal-learning process guarantees that crucial information can be promoted even under shifting social circumstances. Ó 2012 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved. Group-living animals often negotiate social interactions with accompanying vocalizations that may encode information on indi- vidual identity or social group affiliation (Bradbury & Vehrencamp 1998). Vocal signatures are either innate or acquired through vocal production learning (Janik & Slater 1997). Vocal production learning is defined as the imitation of new signals or the social modification of existing signals; the latter seems to be more prev- alent in mammals (Janik & Slater 1997 , 2000; Boughman & Moss 2003). Vocal production learning can affect both individual- and group-specific signals. Learned individual signatures often occur in species that live in fissionefusion societies and form long-lasting social bonds that are maintained vocally (Cortopassi & Bradbury 2006; Janik et al. 2006) whereas learned group signatures are mainly found in species with stable social groups (Boughman 1998; Sharp et al. 2005). Learned group signatures normally originate from social modi- fication (sensu Boughman & Moss 2003), that is, existing vocali- zations of different individuals converge because they are modified in response to social interactions with one another. Signal convergence leads to increased acoustic similarity between signallers (Boughman & Moss 2003). Vocal group signatures can be shared with either social rivals (e.g. dialects or song type matching) or group mates (e.g. duets or group-specific calls) and therefore the social interactions shaping signal convergence can be aggressive or affiliative. Examples of learned signal convergence among rivals include many species of territorial songbirds (Kroodsma & Baylis 1982) but no mammals so far, whereas learned signal conver- gence among group members has been found in both birds and mammals (Boughman & Moss 2003; Tyack 2008) and is sometimes termed horizontal learning (Bertin et al. 2007). Call convergence among group members may have multiple implications ranging from group cohesion under highly mobile circumstances (Ford 1991; Boughman 1998; Hile & Striedter 2000) and affiliative interactions with social partners (Vehrencamp et al. 2003) to the exclusion of nongroup members. In the latter scenario, a vocal group signature functions as a badge or password (summa- rized in Tyack 2008) that allows access to limited resources shared among group members. In contrast to innate vocal group signatures, learned ones offer more flexibility, which is especially important when individuals disperse to a new social group (Wright & Wilkinson 2001), form only temporary associations (Janik & Slater 1998) or when the vocal signature not only encodes the social origin but also the current social affiliations of an individual (Sewall 2009). Generally * Correspondence: M. Knörnschild, Institute for Experimental Ecology, University of Ulm, Albert-Einstein-Allee 11, 89081 Ulm, Germany. E-mail address: mirjam.knoernschild@uni-ulm.de (M. Knörnschild). Contents lists available at SciVerse ScienceDirect Animal Behaviour journal homepage: www.elsevier.com/locate/anbehav 0003-3472/$38.00 Ó 2012 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.anbehav.2012.06.029 Animal Behaviour xxx (2012) 1e9 Please cite this article in press as: Knörnschild, M., et al., Learned vocal group signatures in the polygynous bat Saccopteryx bilineata, Animal Behaviour (2012), http://dx.doi.org/10.1016/j.anbehav.2012.06.029