Cognitive Ethology Laboratory, German Primate Center, Göttingen, Germany.
Neurociencias, Instituto Nacional de Psiquiatría Ramón de la Fuente Muñiz, Mexico City, Mexico.
PLoS One. 2019 Apr 3;14(4):e0213914. doi: 10.1371/journal.pone.0213914. eCollection 2019.
Group living animals produce vocalizations denominated "contact calls" to maintain contact with out-of-sight group members. These calls have been shown to vary with caller identity and distance to potential listeners. However, it is not clear whether the acoustic variation of contact calls is related to caller social isolation (e.g., inside or outside a subgroup) and listeners' responses that can be helpful to maintain contact. Here, we addressed these questions in spider monkeys (Ateles geoffroyi), a Neotropical primate that exchanges contact calls denominated "whinnies", which show graded variation related to caller immediate behavior and distance between callers. Using 566 whinnies produced by 35 free-ranging adult spider monkeys recorded at ≤ 20 m from microphones, we first analyzed whether the acoustic variation of spontaneous whinnies (i.e., whinnies that are not responses to previous whinnies) is related to caller social isolation or whether acoustic variation is related to the likelihood of eliciting a response whinny from another individual. Secondly, we assessed whether listeners' responses (i.e., time to respond vocally, acoustic characteristics of response whinnies, orienting behaviors) were related to the acoustic variation of previous whinnies. Our study revealed that callers that were outside a subgroup produced whinnies with a lower fundamental frequency (F0), which travels longer distances, and increases the likelihood of producing a response whinny. Moreover, listeners (i.e., responders) responded faster to lower F0 whinnies. However, the acoustic variation (i.e., F0 variation) in response whinnies was better explained by the separation distance between callers, than by the acoustic variation of the previous whinny. Overall, our results suggest that whinny variation facilitates vocal contact to callers that are outside a subgroup, and that context and whinny variation affect listeners' responses.
群居动物会发出被称为“联络叫声”的声音，以与看不见的群体成员保持联系。这些叫声已经被证明会随着呼叫者的身份和与潜在听众的距离而变化。然而，目前还不清楚联络叫声的声学变化是否与呼叫者的社会隔离（例如，在子群内或外）有关，以及听众的反应是否有助于保持联系。在这里，我们在蜘蛛猴（Ateles geoffroyi）中解决了这些问题，蜘蛛猴是一种新热带灵长类动物，它会发出被称为“嘶嘶声”的联络叫声，这些叫声与呼叫者的即时行为和呼叫者之间的距离有关，呈现出分级变化。使用 35 只自由放养的成年蜘蛛猴在距离麦克风≤20 米的范围内录制的 566 次嘶嘶声，我们首先分析了自发嘶嘶声（即不是对先前嘶嘶声的响应）的声学变化是否与呼叫者的社会隔离有关，或者声学变化是否与引起另一个个体响应嘶嘶声的可能性有关。其次，我们评估了听众的反应（即响应发声的时间、响应嘶嘶声的声学特征、定向行为）是否与先前嘶嘶声的声学变化有关。我们的研究表明，处于子群之外的呼叫者发出的嘶嘶声的基频（F0）较低，传播距离较远，并且更有可能产生响应嘶嘶声。此外，听众（即响应者）对低 F0 嘶嘶声的响应更快。然而，响应嘶嘶声的声学变化（即 F0 变化）更好地由呼叫者之间的分离距离来解释，而不是由前一声嘶嘶声的声学变化来解释。总的来说，我们的结果表明，嘶嘶声的变化有助于与子群外的呼叫者进行声音接触，并且上下文和嘶嘶声的变化会影响听众的反应。
