Vocal information and the navigation of social decisions in bats: Is social complexity linked to vocal complexity?

Abstract

To make adaptive behavioural decisions, animals must acquire and process information from their natural and social environment. Reducing uncertainty regarding the actions and goals of conspecifics is especially important for group‐living animals. Bats are often highly gregarious and use versatile social vocalizations to mediate social interactions. These social vocalizations encode a substantial amount of ecologically relevant information, such as individual identity, sex and kin. Decoding this information enables receivers to make informed decisions on resource allocation, mate choice, territorial defence and cooperation. Erroneous decisions on such crucial aspects of bats’ social behaviour can be costly due to reduced reproductive success or survival. Increasingly complex social interactions require social vocalizations encoding more information which, in turn, could facilitate the evolution of even more complex social interactions. Evidence for the positive correlation of social and vocal complexity is available for several taxa but is currently very limited for bats. We conducted a phylogenetic comparative analysis to link the information content encoded in bats’ social vocalizations to the complexity of their social lives, that is the level of uncertainty associated with assessing individual identity. We focused on three different vocalization types encoding individual signatures (pup isolation calls, adult contact calls and male‐specific vocalizations). Information content in bit (i.e. the number of binary decisions necessary to discriminate among N individuals) was used as an estimate of vocal complexity; relevant social group size (i.e. the number of conspecifics whose identity a receiver could confuse) was used as an estimate of social complexity. Our phylogenetic comparative analysis detected a positive relationship between the information content of vocalizations and the respective relevant social group size. This relationship suggests a positive feedback loop between social and vocal complexity for bat vocalizations and highlights the importance of vocal information for negotiating fitness‐relevant social decisions of bats. In conclusion, our work suggests that social complexity drives vocal complexity in bats. Future studies on other hitherto understudied taxa are necessary to establish a comprehensive theory on the multi‐faceted co‐evolution of sociality and communication in the animal kingdom. A free Plain Language Summary can be found within the Supporting Information of this article.

Vocal repertoire, micro-geographical variation and within-species acoustic partitioning in a highly colonial pinniped, the Cape fur seal

“…This includes the physical characteristics of the signals produced, the quantity of information they convey, the specific properties of features encoding information but also the cognitive abilities of the individuals to analyse the received signal. Evidence for a positive correlation between social and vocal complexity is found in several taxa: birds [ 10 ], bats [ 11 ], rodents [ 12 ], primates [ 13 ], mongoose species [ 14 ], whales [ 15 ] and phocid seals [ 16 , 17 ]. For species living in dense groups, vocal complexity usually causes an increase in the vocal repertoire size.…”

“…In such a constrained environment, it is particularly challenging for emitters to produce signals in which information is surely and reliably conveyed. From the receiver perspective, reducing uncertainty regarding the identity (age, sex, social or reproductive status) of a signalling conspecific and decoding the information contained in the received signal is crucial to respond to a given situation [ 11 ]. We investigate how CFSs may overcome these constraints and minimize interference among conspecifics.…”

The role of sensory ecology and cognition in social decisions: Costs of acquiring information matter

“…Knörnschild, Fernandez, and Nagy () compare the complexity of calls, and the role of complex social environments for intraspecific communication between different species of bats. Bat calls encode information on individual identity, sex and relatedness, which receivers can use to make decisions about mate choice, territorial defence, resource allocation and cooperation.…”

Extreme ecological constraints lead to high degree of individual stereotypy in the vocal repertoire of the Cape fur seal (Arctocephalus pusillus pusillus)

“…In these gregarious species, social interactions are complicated by the simultaneous co-existence of many individuals (Aubin and Jouventin 1998): animals frequently interact with many different individuals in a variety of social contexts. It is therefore crucial that animals are able to accurately identify surrounding conspecifics to be able to adjust their behavioural responses accordingly, with the aim of limiting interactions to relevant situations only (Knörnschild et al 2020). An understanding of individual recognition processes in these socially complex species would improve our ability to decipher communication strategies in animal species.…”