Department of Biological Sciences, Royal Holloway University of London, Egham, Surrey TW20 0EX, UK; Centre for Ecology and Conservation, University of Exeter, Penryn Campus, Penryn, Cornwall TR10 9FE, UK.
Groningen Institute for Evolutionary Life Sciences, University of Groningen, Centre for Life Sciences, Nijenborgh 7, 9747 Groningen, the Netherlands.
Curr Biol. 2021 Jul 26;31(14):3192-3198.e7. doi: 10.1016/j.cub.2021.05.009. Epub 2021 Jun 4.
The "selfish herd" hypothesis provides a potential mechanism to explain a ubiquitous phenomenon in nature: that of non-kin aggregations. Individuals in selfish herds are thought to benefit by reducing their own risk at the expense of conspecifics by attracting toward their neighbors' positions or central locations in the aggregation. Alternatively, increased alignment with their neighbors' orientation could reduce the chance of predation through information sharing or collective escape. Using both small and large flocks of homing pigeons (Columba livia; n = 8-10 or n = 27-34 individuals) tagged with 5-Hz GPS loggers and a GPS-tagged, remote-controlled model peregrine falcon (Falco peregrinus), we tested whether individuals increase their use of attraction over alignment when under perceived threat. We conducted n = 27 flights in treatment conditions, chased by the robotic "predator," and n = 16 flights in control conditions (not chased). Despite responding strongly to the RobotFalcon-by turning away from its flight direction-individuals in treatment flocks demonstrated no increased attraction compared with control flocks, and this result held across both flock sizes. We suggest that mutualistic alignment is more advantageous than selfish attraction in groups with a high coincidence of individual and collective interests (adaptive hypothesis). However, we also explore alternative explanations, such as high cognitive demand under threat and collision avoidance (mechanistic hypotheses). We conclude that selfish herd may not be an appropriate paradigm for understanding the function of highly synchronous collective motion, as observed in bird flocks and perhaps also fish shoals and highly aligned mammal aggregations, such as moving herds.
“自私羊群”假说提供了一种潜在的机制，可以解释自然界中一种普遍存在的现象：非亲缘聚集。自私羊群中的个体通过吸引邻居的位置或聚集体的中心位置，以牺牲同种个体为代价来降低自身风险，从而受益。或者，通过信息共享或集体逃避，与邻居的方向更加一致，可能会降低被捕食的机会。我们使用带有 5-Hz GPS 记录仪的小型和大型归巢鸽（Columba livia；n = 8-10 或 n = 27-34 只）和带有 GPS 标记的远程控制的游隼（Falco peregrinus）模型标记个体，测试了个体在感知到威胁时是否会增加对吸引力的使用而不是对对齐的使用。我们在处理条件下进行了 n = 27 次飞行，由机器人“捕食者”追逐，在控制条件下进行了 n = 16 次飞行（未追逐）。尽管个体对“机器猎隼”做出了强烈的反应——远离其飞行方向——但处理群中的个体与对照组相比，没有表现出增加的吸引力，而且这个结果在两种群大小中都成立。我们认为，在个体利益和集体利益高度一致的群体中，互惠对齐比自私吸引更有利（适应假说）。然而，我们也探讨了其他解释，例如在受到威胁和避免碰撞时的高认知需求（机制假说）。我们得出结论，自私羊群假说可能不适用于理解高度同步的集体运动的功能，这种运动在鸟类群体中观察到，也许在鱼类鱼群和高度对齐的哺乳动物聚集中也观察到，例如移动的羊群。
