Risso' s dolphins plan foraging dives

Humans remember the past and use that information to plan future actions. Lab experiments that test memory for the location of food show that animals have a similar capability to act in anticipation of future needs, but less work has been done on animals foraging in the wild. We hypothesized that planning abilities are critical and common in breath-hold divers who adjust each dive to forage on prey varying in quality, location, and predictability within constraints of limited oxygen availability. We equipped Risso &' s dolphins with sound-and-motion-recording tags to reveal where they focus their attention through their externally observable echolocation and how they fine-tune search strategies in response to expected and observed prey distribution. The dolphins &' information was integrated with synoptic prey data obtained from echosounders on an underwater vehicle. At the start of the dives, whales adjusted their echolocation inspection ranges in ways that suggest planning to forage at a particular depth. Once entering a productive prey layer, dolphins reduced their search range comparable to the scale of patches within the layer, suggesting that they were using echolocation to select prey within the patch. On ascent, their search range increased, indicating that they decided to stop foraging within that layer and started searching for prey in shallower layers. Information about prey, learned throughout the dive, was used to plan foraging in the next dive. Our results demonstrated that planning for future dives was modulated by spatial memory derived from multi-modal prey sampling (echoic, visual, and capture) during earlier dives.

人类能够铭记过往经验，并依托此类信息规划未来行动。针对食物位置记忆的实验室实验表明，动物具备类似的、为满足未来需求而提前行动的能力，但针对野生动物觅食行为的相关研究仍较为匮乏。我们提出假设：在需调控每次潜水时长以觅食的屏息型潜水动物中，规划能力至关重要且普遍存在——这类动物需在氧气储量有限的约束下，针对质量、位置与可预测性各不相同的猎物开展觅食活动。我们为里氏海豚（Risso's dolphins）安装了声动记录标签（sound-and-motion-recording tags），通过其可被外部观测到的回声定位（echolocation）行为，解析其注意力聚焦区域，并探究它们如何根据预期与实测的猎物分布情况，精准调整搜索策略。我们将海豚采集的相关信息，与通过水下运载器（underwater vehicle）搭载的回声测深仪（echosounders）获取的同步猎物数据进行整合。在潜水起始阶段，海豚会调整其回声定位的探测范围，这一行为暗示它们已规划好在特定深度开展觅食活动。一旦进入猎物丰度较高的水层，海豚会将搜索范围缩小至与该水层内猎物斑块尺度相当的水平，这表明它们正通过回声定位在斑块内部筛选猎物。在上浮过程中，海豚的搜索范围会扩大，这意味着它们已决定终止该水层内的觅食活动，转而开始在更浅的水层中搜寻猎物。它们在本次潜水过程中获取的猎物相关信息，会被用于规划下一次潜水的觅食行为。我们的研究结果表明，针对未来潜水的觅食规划，会受到此前潜水过程中通过多模态猎物采样（multi-modal prey sampling，包括回声、视觉与捕获尝试）所获得的空间记忆的调控。