Data from: Daily foraging patterns in free-living birds: exploring the predation-starvation trade-off

Daily patterns in the foraging behaviour of birds are assumed to balance the counteracting risks of predation and starvation. Predation risks are a function of the influence of weight on flight performance and foraging behaviours that may expose individuals to predators. Although recent research sheds light on daily patterns in weight gain, little data exist on daily foraging routines in free-living birds. In order to test the predictions of various hypotheses about daily patterns of foraging, we quantified the activity of four species of passerines in winter using radio frequency identification receivers built into supplemental feeding stations. From records of 472,368 feeder visits by tagged birds, we found that birds generally started to feed before sunrise and continued to forage at a steady to increasing rate throughout the day. Foraging in most species terminated well before sunset, suggesting their desired level of energy reserves was being reached before the end of the day. These results support the risk-spreading theorem over a long-standing hypothesis predicting bimodality in foraging behaviour purportedly driven by a tradeoff between the risks of starvation and predation. Given the increased energetic demands experienced by birds during colder weather, our results suggest that birds’ perceptions of risk are biased towards starvation avoidance in winter.

鸟类觅食行为的日节律被认为是在权衡捕食与饥饿这两种相互拮抗的风险。捕食风险取决于体重对飞行能力的影响，以及可能使个体暴露于捕食者视野的觅食行为。尽管近期研究已阐明体重增加的日节律模式，但针对野生鸟类日常觅食规律的相关数据仍较为匮乏。为验证各类关于觅食日节律的假说预测，我们采用安装于补充喂食站内的射频识别（radio frequency identification）接收装置，对冬季4种雀形目鸟类（passerines）的活动进行了量化分析。通过对佩戴标记的鸟类共计472368次喂食器到访记录的分析，研究团队发现，鸟类通常会在日出前开始觅食，并在全天以稳定至逐步提升的频率持续觅食活动。多数雀形目鸟类的觅食活动会在日落前较早时段结束，这表明它们会在当日结束前达成预期的能量储备水平。相较于长期以来认为觅食行为呈双峰模式、据称由饥饿与捕食风险权衡所驱动的经典假说，本研究结果更支持风险分散定理。考虑到鸟类在寒冷天气中面临的能量需求显著提升，本研究结果表明，冬季鸟类的风险感知偏向于规避饥饿。