Vocal Mimicry of Alarm-Associated Sounds by a Drongo Elicits Flee and Mobbing Responses from Other Species that Participate in Mixed-Species Bird Flocks

A growing number of studies have shown that vocal mimicry appears to be adaptive for some bird species, although the exact function of this behaviour varies among species. Previous work has looked at the function of the vocal mimicry of non-alarm sounds by the Greater Racket-tailed Drongo (Dicurus paradiseus). But drongos also imitate sounds associated with danger, such as predators' vocalisations or the mobbing-specific vocalisations of other prey species, raising the question of whether the function of mimicry can vary even within a species. In a playback experiment, we compared the effect on other species of different drongo vocalisations including: (1) predator mimicry, (2) mobbing mimicry, (3) drongo species-specific alarms, (4) drongo species-specific non-alarms and (5) a control (barbet) sound. Both mobbing mimicry and drongo species-specific alarms elicited flee responses from the most numerous species in the flocks, the Orange-billed Babbler (Turdoides rufescens). Mobbing mimicry also elicited mobbing responses from the Orange-billed Babbler and from another gregarious babbler, the Ashy-headed Laughingthrush (Garrulax cinereifrons); when responses from both species were considered together, they were elicited at a significantly higher level by mobbing mimicry than by the barbet control, and a level that tended to be higher (0.07 <0.10) than the response to drongo-specific alarms. Predator mimicry elicited flee and mobbing responses at an intermediary level. Our results support the hypotheses that mobbing mimicry is a specific category of mimicry that helps attract the aid of heterospecifics during mobbing and that alarm mimicry can in some cases be beneficial to the caller.