To eat and not be eaten: diurnal mass gain and foraging strategies in wintering great tits

Adaptive theory predicts that the fundamental trade-off between starvation and predation risk shapes diurnal patterns in foraging activity and mass gain in wintering passerine birds. Foragers mitigating both types of risk should exhibit a bimodal distribution (increased foraging and mass gain early and late in the day), whereas both foraging and mass gains early (vs. late) during the day are expected when the risk of starvation (vs. predation) is greatest. Finally, relatively constant rates of foraging and mass gain should occur when the starvation-predation risk trade-off is independent of body mass. Using automated feeders with integrated digital balances, we estimated diurnal patterns in foraging and body mass gain to test which ecological scenario was best supported in wintering great tits Parus major. Based on data of 40 consecutive winter days recording >12 000 body masses of 28 individuals, we concluded that birds foraged and gained mass early during the day, as predicted by t...

适应性理论预测，饥饿风险与捕食风险之间的核心权衡，塑造了越冬雀形目鸟类觅食活动与体重增加的昼夜节律模式。同时规避两类风险的觅食者应呈现双峰分布（即在清晨与傍晚时段提升觅食强度与体重增长速率）；而当饥饿风险（相较于捕食风险）达到峰值时，预计觅食活动与体重增长会集中在日间早期（而非晚期）。最后，若饥饿-捕食风险权衡与个体体重无关，则觅食活动与体重增长的速率应保持相对稳定。本研究采用集成数字秤的自动喂食器，通过估算觅食与体重增长的昼夜节律模式，检验越冬大山雀（Parus major）最符合哪一种生态情景。基于连续40个冬日的观测数据，共记录28只个体的超过12000次体重测量值，我们得出结论：鸟类会在日间早期开展觅食活动并增加体重，这与t...所预测的结果一致。