Beaked whales and state-dependent decision-making: how does body condition affect the trade-off between foraging and predator avoidance?

Body condition is central to how animals balance foraging with predator-avoidance – a trade-off that fundamentally affects animal fitness. Animals in poor condition may accept greater predation risk to satisfy current foraging “needs”, whilst those in good condition may be more risk averse to protect future “assets”. These state-dependent behavioural predictions can help interpret responses to human activities, but are little explored in marine animals. This study investigates the influence of body condition on how beaked whales trade off foraging and predator-avoidance. Body density (indicating lipid-energy stores) was estimated for 15 foraging northern bottlenose whales tagged near Jan Mayen, Norway. Composite indices of foraging (diving and echolocation clicks) and anti-predation (long ascents, non-foraging dives and silent periods reducing predator eavesdropping) were negatively related. Experimental sonar exposures led to decreased foraging and increased risk aversion, confirming a foraging/perceived safety trade-off. However, lower lipid stores were not related to a decrease in predator-avoidance versus foraging, i.e. worse condition animals did not prioritise foraging. Individual differences (‘personalities’) or reproductive context could offer alternative explanations for the observed state-behaviour relationships. This study provides evidence of foraging/predator-avoidance trade-offs in a marine top predator and demonstrates that animals in worse condition might not always take more risks.

身体状态是动物权衡觅食与避敌行为的核心驱动因素——这种生存权衡从根本上影响动物的适合度。身体状态较差的个体可能会承受更高的捕食风险，以满足当前的觅食需求；而身体状态良好的个体则更倾向于规避风险，以保护其未来的生存资本。这类依赖身体状态的行为预测有助于解读动物对人类活动的响应，但目前海洋动物中的相关研究仍较为匮乏。本研究以喙鲸为研究对象，探讨身体状态对其权衡觅食与避敌行为的影响。研究人员对挪威扬马延岛附近被标记的15头正在觅食的北瓶鼻鲸的身体密度进行了估算，该指标可反映其体内的脂质能量储备。觅食综合指数（涵盖潜水行为与回声定位咔声）与反捕食综合指数（包括长距离上浮、非觅食潜水以及降低被捕食者窃听风险的静默期）呈显著负相关。实验性声纳暴露使北瓶鼻鲸的觅食行为减少、风险规避行为增加，证实了觅食与感知安全之间存在权衡关系。但脂质储备较低的个体并未在觅食与避敌之间更倾向于降低避敌行为，换言之，身体状态较差的个体并未将觅食置于优先地位。个体差异（即“个性”）或繁殖背景，或许可以为本次研究中观察到的身体状态与行为之间的关联提供替代性解释。本研究为海洋顶级捕食者存在觅食与避敌的权衡提供了实证依据，并表明身体状态较差的动物并非总会承担更高的捕食风险。