No Effect of Note Order on the Response of Coal Tits to Conspecific, Heterospecific and Artificial Mobbing Calls

Most Parid species produce specific, order-constrained mobbing calls. These calls elicit responses from both conspecifics and heterospecifics, with evidence indicating that such responses occur only when the calls are organised in this specific order. One notable exception is the coal tit (Periparus ater), a species that employs similar types of notes, yet does not exhibit clear order constraints within its mobbing sequences. Despite this apparent absence of order constraints, a recent experiment has demonstrated that coal tits may be sensitive to the order of notes in heterospecific calls. Therefore, the relative significance of note order in conspecific and heterospecific communication among coal tits remains unclear. We conducted a playback experiment to examine the effects of note order (natural coal tit order, typical Parid order and reversed order) and species identity (conspecific, familiar heterospecific—the great tit, Parus major, or artificial notes) on coal tit mobbing responses. Our findings indicate that coal tits exhibited a strong response to conspecific calls, regardless of the order of the notes; conversely, they displayed little to no response to heterospecific calls and artificial notes, irrespective of note order. A similar pattern was observed when assessing the general community response. This unexpectedly low response to familiar heterospecific calls may be attributable to a reduced density of great tits in the area we tested: ecological factors, such as community composition, may influence heterospecific mobbing behaviours and the subsequent biological interpretations of playback experiments. This study also underscores the necessity of conducting comparative research on closely related species to evaluate the potential generality of findings, such as strong order constraints recently observed in great tits and Japanese tits.