Bird predation poses a strong selection pressure on fish. Since birds must enter the water to catch fish, a combination of visual and mechano-acoustic cues (multimodal) characterize an immediate attack, while single cues (unimodal) may represent less dangerous disturbances. We investigated whether fish could use this information to distinguish between non-threatening and dangerous events and adjust their antipredator response to the perceived level of risk. To do so, we investigated the antipredator behavior of the sulphur molly (Poecilia sulphuraria), a small freshwater fish which is almost exclusively preyed on by piscivorous birds in its endemic sulfide spring habitat. In a field survey, we confirmed that these fish frequently have to distinguish between disturbances stemming from attacking birds (multimodal) and those which pose no (immediate) threat such as bird overflights (unimodal). In a laboratory experiment, we then exposed fish to artificial visual and/or acoustic stimuli presented separately or combined. Sensitivity was high regardless of stimulus type and number (more than 96% of fish initiated diving), but fish dove deeper, faster, and for longer when both stimuli were available simultaneously. Based on the system’s high rates of bird activity, we argue that such an unselective dive initiation with subsequent fine-tuning of diving parameters in accordance to cue modality represents an optimal strategy for these fish to save energy necessary to respond to future attacks. Ultimately, our study shows that fish anticipate the imminent risk posed by disturbances linked to bird predation through integrating information from both visual and acoustic cues.

中文翻译：

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声音和视觉刺激相结合，促进鱼类对空中捕食的更强反应

鸟类捕食对鱼类造成强大的选择压力。由于鸟类必须进入水中才能捕鱼，因此视觉和机械声学提示（多模式）的组合表征了立即攻击，而单一提示（单模式）可能代表危险性较小的干扰。我们研究了鱼类是否可以利用这些信息来区分非威胁性事件和危险事件，并根据感知到的风险水平调整其反捕食者反应。为此，我们研究了硫鳅（Poecilia sulfuraria）的反捕食行为，这是一种小型淡水鱼，在其特有的硫化物泉栖息地几乎完全被食鱼鸟类捕食。在一项实地调查中，我们证实这些鱼经常必须区分由攻击鸟类（多模式）引起的干扰和不构成（直接）威胁的干扰，例如鸟类飞越（单模式）。在实验室实验中，我们将鱼暴露于单独或组合的人工视觉和/或听觉刺激。无论刺激类型和数量如何，敏感性都很高（超过 96% 的鱼开始潜水），但当两种刺激同时存在时，鱼会潜入更深、更快、时间更长。基于该系统的鸟类活动率很高，我们认为这种不加选择的潜水启动以及随后根据提示模式微调潜水参数代表了这些鱼节省应对未来攻击所需的能量的最佳策略。最终，我们的研究表明，鱼类通过整合视觉和听觉线索的信息来预测与鸟类捕食相关的干扰所带来的迫在眉睫的风险。