Abstract
Individual recognition is critical in social animal communication, but it has not been demonstrated for a complete vocal repertoire. Deciphering the nature of individual signatures across call types is necessary to understand how animals solve the problem of combining, in the same signal, information about identity and behavioral state. We show that distinct signatures differentiate zebra finch individuals for each call type. The distinctiveness of these signatures varies: contact calls bear strong individual signatures while calls used during aggressive encounters are less individualized. We propose that the costly solution of using multiple signatures evolved because of the limitations of the passive filtering properties of the birds’ vocal organ for generating sufficiently individualized features. Thus, individual recognition requires the memorization of multiple signatures for the entire repertoire of conspecifics of interests. We show that zebra finches excel at these tasks.
Highlights
Humans share the ability to recognize familiar individuals using vocal-cues with many other animal species that rely on individual-specific relationships, such as mated pair bonds, the mother−young bond, or the tolerance relationship developed by neighbor territorial animals (e.g. Birds[1,2,3]; Mammals[4,5,6,7]; Amphibians[8,9]; reviewed in refs. 10–12)
Re and NoRe vocalizations can correspond to two different stimuli, two sets of renditions of one call type for two different birds, two sets of renditions from all call types mixed together
Individual recognition across multiple call types could be useful, for example, to assess the reliability of the information provided by specific individuals[7] or to promote general collaborative or avoidant behavior with particular individuals
Summary
Humans share the ability to recognize familiar individuals using vocal-cues with many other animal species that rely on individual-specific relationships, such as mated pair bonds, the mother−young bond, or the tolerance relationship developed by neighbor territorial animals (e.g. Birds[1,2,3]; Mammals[4,5,6,7]; Amphibians[8,9]; reviewed in refs. 10–12). Social animals have complex vocal repertoires comprised of multiple call types that they use to communicate different behavioral states (e.g. alarm, hunger, need for contact). Individual information in animals could be the result of morphological individual differences in the vocal apparatus that would cause similar passive shaping of the sound across all calls in one’s repertoire: the passive-voice-cues[24]. Using operant conditioning design to measure behavioral discriminability and acoustic analyses to determine the features that carry individual information, we perform a thorough comparison of individual signatures across the repertoire of the zebra finch. We find that zebra finches do not produce signatures that generalize across call types but instead generate call-type-specific individual signatures The strength of this signature varies across call types and is stronger for social contact calls. Birds are able to identify a vocalizer irrespective of call type, a task that requires the memorization of a set of vocal signatures
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