Avian vocal mimicry: a unified conceptual framework

Abstract

Mimicry is a classical example of adaptive signal design. Here, we review the current state of research into vocal mimicry in birds. Avian vocal mimicry is a conspicuous and often spectacular form of animal communication, occurring in many distantly related species. However, the proximate and ultimate causes of vocal mimicry are poorly understood. In the first part of this review, we argue that progress has been impeded by conceptual confusion over what constitutes vocal mimicry. We propose a modified version of Vane-Wright's (1980) widely used definition of mimicry. According to our definition, a vocalisation is mimetic if the behaviour of the receiver changes after perceiving the acoustic resemblance between the mimic and the model, and the behavioural change confers a selective advantage on the mimic. Mimicry is therefore specifically a functional concept where the resemblance between heterospecific sounds is a target of selection. It is distinct from other forms of vocal resemblance including those that are the result of chance or common ancestry, and those that have emerged as a by-product of other processes such as ecological convergence and selection for large song-type repertoires. Thus, our definition provides a general and functionally coherent framework for determining what constitutes vocal mimicry, and takes account of the diversity of vocalisations that incorporate heterospecific sounds. In the second part we assess and revise hypotheses for the evolution of avian vocal mimicry in the light of our new definition. Most of the current evidence is anecdotal, but the diverse contexts and acoustic structures of putative vocal mimicry suggest that mimicry has multiple functions across and within species. There is strong experimental evidence that vocal mimicry can be deceptive, and can facilitate parasitic interactions. There is also increasing support for the use of vocal mimicry in predator defence, although the mechanisms are unclear. Less progress has been made in explaining why many birds incorporate heterospecific sounds into their sexual displays, and in determining whether these vocalisations are functionally mimetic or by-products of sexual selection for other traits such as repertoire size. Overall, this discussion reveals a more central role for vocal mimicry in the behavioural ecology of birds than has previously been appreciated. The final part of this review identifies important areas for future research. Detailed empirical data are needed on individual species, including on the structure of mimetic signals, the contexts in which mimicry is produced, how mimicry is acquired, and the ecological relationships between mimic, model and receiver. At present, there is little information and no consensus about the various costs of vocal mimicry for the protagonists in the mimicry complex. The diversity and complexity of vocal mimicry in birds raises important questions for the study of animal communication and challenges our view of the nature of mimicry itself. Therefore, a better understanding of...

Causes and Consequences of Behavioral Interference between Species

“…Numerous examples of interspecific competitive mimicry have been proposed [31,32,35,36,67]. For example, males of a subordinate species might gain access to prime habitat by mimicking females of a dominant species [34] and juveniles of one species might gain foraging access to the territories of a dominant species by mimicking the adults of a third, noncompetitor species [68].…”

“…Just as interference competition for mates and other resources is thought to have led to the evolution of alternative strategies within species (e.g., territory holders, mate guarders, female mimics, or sneakers), interference competition between species can to lead to the evolution of distinct species roles, with strategies similar to their intraspecific analogs, including various forms of competitive mimicry (Figure 1) [31][32][33][34][35][36][37]. For example, in theory, asymmetries in social dominance between competing species can lead to mimicry of dominant species by subordinate species [33,37].…”

“…Convergence in agonistic signals and competitor recognition increases the probability that heterospecifics are recognized as competitors and, thus, can not only increase the frequency of aggressive interactions between species, but also reduce interaction costs when the traits involved are dominance or territory deterrence signals that reduce the likelihood or intensity of direct confrontations [1,30]. Interaction costs can also be reduced by learning (Box 4).Just as interference competition for mates and other resources is thought to have led to the evolution of alternative strategies within species (e.g., territory holders, mate guarders, female mimics, or sneakers), interference competition between species can to lead to the evolution of distinct species roles, with strategies similar to their intraspecific analogs, including various forms of competitive mimicry (Figure 1) [31][32][33][34][35][36][37]. For example, in theory, asymmetries in social dominance between competing species can lead to mimicry of dominant species by subordinate species [33,37].…”

“…At a community level, signal design and the timing of signal production can be partitioned to reduce interference, such as when the acoustic mating signals and responses of anurans are differentiated to avoid interactions between heterospecifics [64,65]. Alternatively, if aggressive signaling is adaptive, for example when it mediates interspecific territoriality, signal design can converge and signaling schedules can become behaviorally synchronized among species [66].Numerous examples of interspecific competitive mimicry have been proposed [31,32,35,36,67]. For example, males of a subordinate species might gain access to prime habitat by mimicking females of a dominant species [34] and juveniles of one species might gain foraging access to the territories of a dominant species by mimicking the adults of a third, noncompetitor species [68].…”

Crying wolf to a predator: deceptive vocal mimicry by a bird protecting young

“…Yet surprisingly, how predators respond to mimetic vocalizations of prey has never been tested. As a result, avian vocal mimicry is often placed outside the evolutionary framework of traditional mimicry systems (for discussions, see [10,15]). …”