Understanding predator–prey relationships is fundamental in many areas of ecology and conservation. In reptiles, basking time often increases the risk of predation and one way to minimise this risk is to reduce activity time and to stay within a refuge. However, this implies costs of lost opportunities for foraging, reproduction, and thermoregulation. We aimed to determine the main potential and observed predators of Vipera graeca, to infer predation pressure by estimating the incidence and the body length and sex distribution of predation events based on body injuries, and to assess whether and how the activity of V. graeca individuals is modified by predation pressure. We observed n = 12 raptor bird species foraging at the study sites, of which Circaetus gallicus, Falco tinnunculus and Corvus cornix were directly observed as predators of V. graeca. We found injuries and wounds on 12.5% of the studied individuals (n = 319). The occurrence of injuries was significantly positively influenced by the body length of vipers, and was more frequent on females than on males, while the interaction of length and sex showed a significant negative effect. The temporal overlap between predator and viper activity was much greater for the vipers’ potential activity than their realised activity. Vipers showed a temporal shift in their bimodal daily activity pattern as they were active earlier in the morning and later in the afternoon than could be expected based on the thermal conditions. The time spent being active on the surface has costs to snakes: predation-related injuries increased in frequency with length, were more frequent in females than in males and occurred in shorter length for males than for females. Our results suggest that vipers do not fully exploit the thermally optimal time window available to them, likely because they shift their activity to periods with fewer avian predators.

中文翻译：

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当风带来翅膀时躲藏或死亡：山蛇通过活动转移来避免捕食者

了解捕食者与猎物的关系是生态学和保护的许多领域的基础。在爬行动物中，晒太阳的时间通常会增加被捕食的风险，而将这种风险降至最低的一种方法是减少活动时间并留在避难所内。然而，这意味着失去觅食、繁殖和体温调节机会的代价。我们的目的是确定 Vipera graeca 的主要潜力和观察到的捕食者，通过基于身体伤害估计捕食事件的发生率和体长和性别分布来推断捕食压力，并评估 V. graeca 个体的活动是否以及如何进行被捕食压力改变。我们观察到 n = 12 种猛禽在研究地点觅食，其中直接观察到 Circaetus gallicus、Falco tinnunculus 和 Corvus cornix 作为 V. 希腊。我们在 12.5% 的研究对象 (n = 319) 身上发现了损伤和伤口。受伤的发生受毒蛇体长的显着正向影响，雌性比雄性更频繁，而长度和性别的交互作用则显示出显着的负向影响。捕食者和毒蛇活动之间的时间重叠对于毒蛇的潜在活动而言比其实际活动要大得多。毒蛇在他们的双峰日常活动模式中表现出时间上的变化，因为他们在早上早些时候和下午晚些时候活跃，而不是根据热条件可以预期的。在水面上活动的时间对蛇来说是有代价的：捕食相关伤害的频率随着长度的增加而增加，女性比男性更常见，男性比女性更短。我们的研究结果表明，毒蛇没有充分利用它们可用的最佳热时间窗口，这可能是因为它们将活动转移到鸟类捕食者较少的时期。