Development of Meaningful Vocal Signals in a Juvenile Territorial Songbird (Gymnorhina tibicen) and the Dilemma of Vocal Taboos Concerning Neighbours and Strangers.

Gisela Kaplan

doi:10.3390/ani8120228

Abstract

Simple SummaryOwnership of a territory is very important for many vertebrates. Some songbird species, such as the Australian magpie, have all-year-round, not just seasonal, territories. Hence, there is a good deal at stake in holding on to such a territory. It requires vigilance, experience, an excellent memory, and most of all, effective vocal communication. There is a strong relationship between successful territorial ownership, strong social bonds, and the health, survival, even the life-span and overall cognitive development of offspring. Yet, we know next to nothing as to how juveniles acquire their vocal skills and apply these appropriately, including territorial signals. Clearly, juveniles need to learn about territoriality, i.e., learn about potential enemies, recognise which birds are neighbours, and what constitutes an incursion into territory. The results of this extensive field study unexpectedly revealed that juveniles did not use more than half of all the vocalisations adults expressed and they needed a long time (three months post fledging) to distinguish between neighbour and stranger calls, attributing differential importance to each. It also showed that the territorial call was learned but was expected by adults not be used by juveniles, limiting their ability to communicate. A range of other calls associated with territoriality were also not expressed, possibly because only territory owners could do so.Young territorial songbirds have calls to learn, especially calls that may be vital for maintaining territory. Territoriality is largely reinforced and communicated by vocal signals. In their natal territory, juvenile magpies (Gymnorhina tibicen) enjoy protection from predators for 8–9 months. It is not at all clear, however, when and how a young territorial songbird learns to distinguish the meaning of calls and songs expressed by parents, conspecifics, neighbours, and heterospecifics, or how territorial calls are incorporated into the juvenile’s own repertoire. This project investigated acquisition and expression of the vocal repertoire in juvenile magpies and assessed the responses of adults and juveniles to playbacks of neighbour and stranger calls inside their territory. The results reported here identify age of appearance of specific vocalisations and the limits of their expression in juveniles. One new and surprising result was that many types of adult vocalisation were not voiced by juveniles. Playbacks of calls of neighbours and strangers inside the natal territory further established that adults responded strongly but differentially to neighbours versus strangers. By contrast, juveniles needed months before paying any attention to and distinguishing between neighbour and stranger calls and eventually did so only in non-vocal ways (such as referral to adults). These results provide evidence that auditory perception not only includes recognition and memory of neighbour calls but also an assessment of the importance of such calls in the context of territoriality.

Highlights

The results showed at least some evidence, if late in the juvenile development, that playbacks within the natal territory increasingly triggered reactivity to calls of magpies that did not belong to their natal group
The neighbour–stranger discrimination has been discussed in many songbirds but the results in this study suggests a further variant to be considered
Magpies with year-long, and often life-long, territories have a large range of vocal signals concerned with intruders and predators and one main call, carolling, is relatively stereotyped to advertise their territorial ownership

Summary

Introduction

StrongStrong territoriality is vitalistovital many avian species.In some as in Australian magpies territoriality to many avian species.In species, some species, as in Australian magpies (Figure(Figure1, Gymnorhina tibicen, sometimes calledCracticus territories held all are yearheld round.1, Gymnorhina tibicen, sometimes called tibicen), Cracticus tibicen), are territories all yearWhileterritoriality year-round is territoriality is latitudes, rare in high latitudes, some have evolved intoand stable [1] While round.year-round rare in high some species havespecies evolved into stable [1]and even permanent social groups interritories permanent especially lowSouthern latitudes (i.e., even permanent social groups in permanent [2],territories especially [2], in low latitudesin(i.e., Southern and equatorial regions), includingmagpie the Australian magpie (hereafter referredHemisphere andHemisphere equatorial regions), including the Australian (hereafter referred to to as magpie). StrongStrong territoriality is vitalistovital many avian species. In some as in Australian magpies territoriality to many avian species. Cracticus territories held all are yearheld round. 1, Gymnorhina tibicen, sometimes called tibicen), Cracticus tibicen), are territories all year. Whileterritoriality year-round is territoriality is latitudes, rare in high latitudes, some have evolved intoand stable [1] While round. Year-round rare in high some species havespecies evolved into stable [1]. Even permanent social groups interritories permanent especially lowSouthern latitudes (i.e., even permanent social groups in permanent [2],territories especially [2], in low latitudesin(i.e., Southern and equatorial regions), includingmagpie the Australian magpie Hemisphere andHemisphere equatorial regions), including the Australian (hereafter referred to to as magpie)

Methods

Results

Discussion

Conclusion