The generation of functionally referential and motivational vocal signals in mammals

Abstract

Animal vocalizations may be divided into functionally referential calls and motivational calls, depending on whether the calls refer to objects and events in the external environment or whether they are the expression of the internal state of the caller although most call types include probably both kinds of information to a receiver. In this chapter I compare several aspects of these two call categories, including the context in which they are produced and what they refer to, how referential and motivational information is expressed in vocal behavior, and what is their ontogeny and evolution. Functionally referential calls have only been described in the context of encounters with a predator, food resource and in agonistic social interactions. All other animal vocalizations are considered motivational calls, although they may contain some referential information to the receiver regarding the context the caller experiences. Functionally referential signals refer to specific attributes of the eliciting external stimuli and cause an appropriate response in the receivers in the absence of any additional information. Motivational calls alternatively refer not to specific external event, but to the emotional state of the caller. Both, referential and motivational information are expressed in frequency-related acoustic parameters. In addition, referential information, which appears at later age than motivational one, seems also to be expressed in the combination of different call types, whereas motivational information relates more to temporal aspects of calls. The evolution of functionally referential calls is limited to a small number of contexts where receiver’s responses to calls elicited by different attributes of the external stimuli are of high sociobiological benefit. So far, ecological as well as social constraints have been reported as limiting factors.