Screaming calls of Leptodactylus savagei (Smoky Jungle Frog) function as an alarm for conspecifics

Neotropical frogs in the family Leptodactylidae frequently emit a loud scream upon being captured by predators, and the leptodactylid scream call was first classified as a distress call functioning to startle would-be predators into releasing prey frogs. However, other authors have suggested that scream calls function to warn nearby conspecifics of a predator threat (i.e., an alarm call) and/or to attract larger secondary predators to distract or predate the primary predator. In this study, we used a repeated-measures playback experiment to test whether Leptodactylus savagei (Smoky Jungle Frog) in Costa Rica responds to scream calls in ways consistent with it functioning as an alarm call. If scream calls emitted by individuals during predation events also serve to warn nearby conspecifics of a predator threat, we predicted that scream calls would elicit elevated flight responses compared to when advertisement calls or control grey-noise treatments. We observed five primary behavioral responses: individuals flattened their bodies, faced their dens, fled into the dens, faced the audio treatment, and called back with a territorial vocalization. We found that behavioral responses differed by treatment: scream calls elicited a greater proportion of flight responses, whereas advertisement calls appeared to cause individuals to demonstrate more interest in the call (particularly females). Our results suggest that L. savagei respond to screaming calls from conspecifics by fleeing in ways consistent with the call functioning as an alarm. Future studies are needed to test whether scream calls also function as a distress call and/or attract secondary predators.

细趾蟾科（Leptodactylidae）的新热带蛙类在被掠食者捕获时，常会发出响亮的尖叫。最初这类细趾蟾的尖叫被归类为遇险呼叫，其功能是震慑潜在掠食者以使其释放被捕的蛙类。但另有学者提出，尖叫呼叫的功能是向附近的同种个体预警掠食者威胁（即警报呼叫），或是吸引体型更大的次级掠食者，以干扰甚至捕食初级掠食者。本研究采用重复测量回放实验，检验哥斯达黎加的萨维奇细趾蟾（Leptodactylus savagei，Smoky Jungle Frog，烟林蛙）对尖叫呼叫的响应是否符合其作为警报呼叫的功能预期。若个体在掠食事件中发出的尖叫呼叫确实用于向附近同种个体预警掠食者威胁，我们预测：相较于广告鸣叫或对照灰噪音处理组，尖叫呼叫会引发更强的逃逸响应。我们观测到五种主要行为响应：个体将身体贴平地面、朝向巢穴、逃入巢穴、朝向音频播放源，以及以领地鸣唱进行回应。研究发现不同处理组的行为响应存在显著差异：尖叫呼叫引发了更高比例的逃逸行为，而广告鸣叫则似乎让个体对鸣声表现出更强的兴趣，其中雌性个体尤为明显。本研究结果表明，萨维奇细趾蟾会通过逃逸响应来应对同种个体的尖叫呼叫，这与该呼叫作为警报呼叫的功能相符。未来仍需开展相关研究，以验证尖叫呼叫是否同时兼具遇险呼叫功能，或是能够吸引次级掠食者。