Transfer of information between a highly social species and heterospecific community members

Many group-living individuals produce specific vocalizations while mobbing (when individuals move toward and harass a predator), a behavior that can recruit conspecifics. Although these vocalizations may be a source of information for heterospecifics, it remains largely unknown how heterospecifics respond to mobbing calls given by group-living species. In this study, we investigate whether the mobbing calls given by Western Australian magpies (Gymnorhina tibicen dorsalis) lead to the recruitment of heterospecifics. By presenting a taxidermied red fox (Vulpes vulpes)-representing a terrestrial predator threat-to a population of magpies and heterospecific species occupying the same area, we demonstrate that magpie calls given in response to a terrestrial predator recruit heterospecifics to the mobbing event. Heterospecifics are more likely to approach and engage in mobbing behavior when the predator is associated with magpie presence than when magpies are absent. We found that larger magpie groups produced more alarm calls than did smaller groups, but we found no evidence that group size affected heterospecific recruitment to the mobbing site. Therefore, the occurrence of magpie alarm calls, rather than the number of individuals giving alarm calls, seems to be the primary predictor of heterospecific recruitment to a mobbing site. Moreover, we used a playback experiment to test if heterospecifics responded more to single-magpie mobbing alarm calls than to single mobbing alarm calls given by a non-social species (red wattlebird, Anthochaera carunculata). We found that heterospecifics responded more to the playbacks of magpie than to red wattlebird alarm calls. Our study therefore suggests that Australian magpies may play a central role as information sources for heterospecific species during predator detection and mobbing events. Significance statement Mobbing-when individuals move toward and vocalize or harass a predator-is a good example of interspecific communication. Loud vocalizations produced during mobbing behavior have been known to not only modify the behavior of the predator but to also recruit individuals to the mobbing event from a variety of different species. Although the response to heterospecific mobbing calls is becoming well documented, it remains largely unknown how heterospecifics respond to the mobbing calls of group-living species, even though these species can provide significant benefits for heterospecific species sharing the same habitat (via increased vigilance and predator detection rates for example). By presenting a predator model and using a series of playback experiments, we demonstrate that group-living Western Australian magpies may play a central role as information sources during predator detection and mobbing events.

Automated summary

The mobbing calls given by Western Australian magpies can recruit heterospecifics, leading them to approach and engage in mobbing behavior when a predator threat is present. Larger magpie groups produce more alarm calls, but the occurrence of magpie alarm calls rather than the number of individuals giving alarm calls seems to be the primary predictor of heterospecific recruitment. Additionally, heterospecifics respond more to single-magpie mobbing alarm calls than to those given by a non-social species, suggesting that Australian magpies may play a central role as information sources during predator detection and mobbing events.