A marine predator relies on both social cues and frequently updated memory to search for prey

Finding scattered resources is a challenge for marine predators, their search strategies shaping in turn their response to global changes. Three types of search strategies are generally considered: random opportunistic search, reliance on conspicuous social cues or long-term individual fidelity to predictably productive areas. More complex strategies, namely intermediate, composite and/or those varying across time and environmental conditions are likely to prevail but are rarely explored. We investigated memory strategies in Cape gannets, a marine predator heavily relying on social cues, and closely related to the Northern gannet which shows long-term individual foraging fidelity. Repeat GPS tracks within seasons revealed that two different individuals leaving the colony more than three days apart showed random chances to forage in a similar direction, whereas within-individuals, birds persisted in a same direction for longer timescales, reaching random levels only after ten days, or nine consecutive trips. This strategy of transient individual preferences within a breeding season was observed in most individuals, every year. These results suggest a consistent and complex search strategy mixing social cues and private information updated every few days. Our simple approach can readily be applied to other central place foragers to better understand the evolutionary ecology of search strategies.

海洋捕食者寻觅分散分布的资源是一项核心挑战，而它们的搜寻策略反过来也决定了自身对全球变化的响应方式。目前学界普遍认可三类基础搜寻策略：随机机会型搜寻、依赖显著社会线索的搜寻，以及对可预测高产觅食区域具备长期个体忠实性的觅食模式。而更为复杂的策略——包括中间型、复合型，或随时间与环境条件动态调整的策略——或许在自然中更为普遍，但相关研究却鲜有开展。
本研究针对严重依赖社会线索的海洋捕食者开普鲣鸟（Cape gannets）展开记忆策略相关探究，该物种与展现出长期个体觅食忠实性的北方鲣鸟（Northern gannet）亲缘关系密切。季内重复GPS追踪数据显示：离开繁殖群间隔超过三天的两只不同个体，其觅食方向的选择呈现随机相似性；而同一个体则会在更长时间尺度内维持同一飞行方向，仅在十天后或连续完成九次觅食行程后，其方向选择才会趋近随机水平。这种繁殖季内短暂个体偏好的策略，在多数个体中每年均可观测到。
上述结果表明，这是一种兼具一致性与复杂性的搜寻策略，融合了社会线索与每隔数日便会更新的私人觅食信息。本研究采用的简易分析框架可轻松推广至其他中心地觅食者（central place foragers），以助力学界更深入地理解搜寻策略的进化生态学机制。