Batesian mimicry refers to a harmless species protecting itself from predators by mimicking a harmful species. A case of acoustic Batesian mimicry has been proposed in the naturalist literature: it is suspected that birds called like a snake when disturbed in their cavities to deter mammalian predators or repel competitors. To evaluate this hypothesis, we first test the assumption that the hissing sound produced by adult females of a wild cavity-nesting species – the blue tit (Cyanistes caeruleus) – is acoustically similar to the hisses of three wild sympatric snake species. Then, we tested one prediction of this hypothesis which is that the receiver of the signal should react similarly to the snake and bird hisses. To do so, we used, hiss-naïve individuals, without any past experience with predators: the house mouse (Mus musculus domesticus), representing a model of a possible nest competitor. We quantified mouse responses to blue tit and snake hisses and two non-hiss sounds (other blue tit vocalizations and human voices). Our results show that snake hisses and blue tit hisses are structurally more similar to each other than to other blue tit vocalizations and that both hisses provoke comparable levels of anxiety behavior in mice. Taken together, these results are compatible with the hypothesis that blue tits have evolved to mimic the sound of snakes, i.e., the Batesian mimicry hypothesis. We also note however that our results also agree with another hypothesis, suggesting that mechanisms underlying the production and perception of hisses are conserved across vertebrates. Further research is needed to disentangle these two hypotheses. Mimicry is a fascinating illustration of the principles of evolution in communication. In the case of Batesian mimicry, species evolve to resemble other species as a mean of deterring harmful receivers. While visual mimicry has been thoroughly investigated across a wide range of species, vocal mimicry remains less studied. In the present study, we compared the acoustic similarity of the hissing sound produced by female blue tits, a cavity-nesting species, to the hisses of three snake species. Then, we exposed mice, a model of a possible cavity competitor, to bird and snake hisses. We showed that snake and blue tit hisses are acoustically similar and provoke comparable anxiety behaviors in mice. These results are compatible with the hypothesis that blue tits utilize an innate fear response to hisses in mammals, a result that may explain why blue tit hisses have been linked to increased survival by other authors. Furthermore, the results also suggest a conserved function of, and response to, hiss vocalizations across vertebrates.

中文翻译：

---

PC 1 像蛇一样发出嘶嘶声：鸟类发出的嘶嘶声与蛇的嘶嘶声相似，并在哺乳动物模型中引发类似的焦虑行为

贝氏拟态是指无害的物种通过模仿有害物种来保护自己免受捕食者的侵害。博物学文献中提出了一个声学贝氏拟态的案例：怀疑鸟类在它们的腔内受到干扰时会像蛇一样发出叫声，以阻止哺乳动物捕食者或击退竞争对手。为了评估这一假设，我们首先测试了一个假设，即一种野生洞穴筑巢物种——蓝山雀 (Cyanistes caeruleus)——的成年雌性发出的嘶嘶声在声学上与三种野生同域蛇物种的嘶嘶声相似。然后，我们测试了这一假设的一个预测，即信号接收器的反应应该类似于蛇和鸟的嘶嘶声。为此，我们使用了天真的个体，过去没有任何捕食者的经验：家鼠（Mus musculusdomesticus），代表可能的巢竞争对手的模型。我们量化了小鼠对蓝山雀和蛇嘶嘶声以及两种非嘶嘶声（其他蓝山雀发声和人声）的反应。我们的结果表明，蛇嘶嘶声和蓝山雀嘶嘶声在结构上比其他蓝山雀发声更相似，并且这两种嘶嘶声在小鼠中引起的焦虑行为水平相当。综上所述，这些结果与蓝山雀已经进化为模仿蛇的声音的假设相一致，即贝茨模仿假设。然而，我们还注意到，我们的结果也与另一个假设一致，这表明嘶嘶声的产生和感知的机制在脊椎动物中是保守的。需要进一步的研究来解开这两个假设。模仿是交流进化原理的一个引人入胜的例子。在贝氏拟态的情况下，物种进化为与其他物种相似，以此作为威慑有害接收者的手段。虽然视觉模仿已经在广泛的物种中进行了彻底的研究，但声音模仿的研究仍然较少。在本研究中，我们比较了雌性蓝山雀（一种窝巢物种）发出的嘶嘶声与三种蛇类发出的嘶嘶声的声学相似性。然后，我们将老鼠（一种可能的腔竞争者的模型）暴露于鸟类和蛇的嘶嘶声中。我们表明蛇和蓝山雀的嘶嘶声在声学上相似，并在小鼠中引起类似的焦虑行为。这些结果与蓝山雀利用哺乳动物对嘶嘶声的先天恐惧反应的假设一致，这一结果可以解释为什么蓝山雀嘶嘶声与其他作者的生存率增加有关。此外，结果还表明脊椎动物的嘶嘶声具有保守的功能和反应。