Animal signallers are subject to audience effects when they alter communication due to changes in the presence or characteristics of receivers. Studies aimed at understanding audience effects have typically examined effects of conspecific audiences on signaller communication. Less work has focused on heterospecific audiences, which present an important avenue of research for species that participate in mixed-species groups. Here we experimentally tested mixed-species flocks of Carolina chickadees, Poecile carolinensis, and tufted titmice, Baeolophus bicolor, for conspecific and heterospecific audience effects. Birds were trapped from naturally occurring flocks and held in seminatural outdoor aviaries, where we recorded calling. We found that chickadees and titmice were sensitive to the number of conspecifics in flocks when communicating via ‘chick-a-dee’ calls, which are social cohesion calls produced by both species. Chickadees also were sensitive to the number of titmice in flocks, but chick-a-dee calling behaviour in titmice did not differ with regard to the number of chickadees in flocks. Furthermore, when subject to playbacks of simulated risk, chickadees and titmice produced more chick-a-dee calls when more titmice were in a flock. After these playbacks, chickadees produced fewer chick-a-dee calls with increasing numbers of conspecifics in flocks, whereas titmice produced more chick-a-dee calls with increasing numbers of conspecifics in flocks. These results suggest that chickadees and titmice are sensitive to social factors within their mixed-species flocks when communicating, and that chickadees appear more sensitive to heterospecific presence than do titmice. We suggest this is due to the dominance status of the species in these flocks, where titmice are typically dominant over chickadees.

中文翻译：

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混种鸡群的实验操作揭示了异种特定受众对呼唤的影响

当动物信号员由于接收者的存在或特征发生变化而改变通信时，他们会受到观众效应的影响。旨在了解受众影响的研究通常检查特定受众对信号者交流的影响。较少的工作集中在异种特定受众上，这为参与混合物种群体的物种提供了重要的研究途径。在这里，我们通过实验测试了卡罗莱纳山雀、Poecile carolinensis 和簇绒山雀、双色山雀的混种群，以实现同种和异种的观众效果。鸟类被困在自然发生的鸟群中，并被关在半自然的室外鸟舍中，我们在那里记录了呼叫。我们发现山雀和山雀在通过“小鸡”的叫声进行交流时对群中同种动物的数量很敏感，这是两种物种产生的社会凝聚力叫声。山雀对鸡群中山雀的数量也很敏感，但山雀的鸡鸣叫行为与鸡群中山雀的数量没有区别。此外，当进行模拟风险回放时，当更多的山雀在群中时，山雀和山雀会发出更多的鸡鸣声。在这些回放之后，随着群中同种数量的增加，山雀产生了较少的雏鸡叫声，而山雀随着群体中同种数量的增加而产生了更多的小鸡叫声。这些结果表明，山雀和山雀在交流时对其混种群内的社会因素很敏感，而且山雀似乎比山雀对异种存在更敏感。我们认为这是由于这些群体中该物种的优势地位，其中山雀通常比山雀占优势。