Data from: The anti-predator role of within-nest emergence synchrony in sea turtle hatchlings

Group formation is a common behavior among prey species. In egg-laying animals, despite the various factors which promote intra-clutch variation that leads to asynchronous hatching and emergence from nests, synchronous hatching and emergence occurs in many taxa. This synchrony may be adaptive by reducing predation risk, but few data are available in any natural system, even for iconic examples of the anti-predator function of group formation. Here, we show for the first time that increased group size (number of hatchlings emerging together from a nest) reduces green turtle (Chelonia mydas) hatchling predation. This effect was only observed earlier in the night when predation pressure was greatest, indicated by the greatest predator abundance and a small proportion of predators preoccupied with consuming captured prey. Further analysis revealed that the effect of time of day was due to the number of hatchlings already killed in an evening; this, along with the apparent lack of other anti-predatory mechanisms for grouping, suggests synchronous emergence from a nest appears to swamp predators, resulting in an attack abatement effect. Using a system with relatively pristine conditions for turtle hatchlings and their predators provides a more realistic environmental context within which intra-nest synchronous emergence may have evolved.

集群行为是被捕食物种的常见行为。尽管存在多种可引发窝内变异的因素，进而导致孵化及出巢过程出现异步性，但诸多动物类群仍普遍存在同步孵化与同步出巢的现象。这种同步性或可通过降低被捕食风险而具备适应性优势，但目前在任何自然生态系统中，相关研究数据都较为匮乏，即便针对那些以集群反捕食功能为典型代表的类群亦是如此。本研究首次证实：增大集群规模（即同一巢穴中一同出巢的幼龟数量）可有效降低绿海龟（Chelonia mydas）幼龟的被捕食概率。该效应仅在夜间较早时段显现——此时捕食压力达到峰值，具体体现为捕食者种群密度最高，且仅有极小比例的捕食者正忙于进食已捕获的猎物。进一步分析表明，当日时段的效应差异与夜间已被捕杀的幼龟数量直接相关；结合目前尚未发现其他集群反捕食机制的研究现状，可推断巢穴同步出巢行为似乎能够“淹没”捕食者，进而产生攻击抑制效应。本研究依托海龟幼龟与捕食者生态相对原始的研究系统，为探究巢穴内同步出巢行为的演化起源提供了更贴近自然的环境背景。