Data from: Kind to kin: weak interference competition among white stork (Ciconia ciconia) broodmates

Altricial nestlings in structured families show a diverse array of behavioural mechanisms to compete for food, ranging from signalling scrambles to aggressive interference. Rates of filial infanticide are moderately high in white storks. It has been hypothesized that this unusual behaviour is an adaptive parental response to the absence of efficient mechanisms of brood reduction (aggression or direct physical interference) by nestlings. To test this latter assumption, we analyzed video recordings of 41 complete feeding episodes at 32 broods during the first half of the nestling period, when nestlings complete 90% of growth and chick mortality and size asymmetries are highest. Parents delivered food to all nestlings simultaneously by regurgitating on the nest floor. No direct (bill to bill) feeding was recorded. Senior nestlings were never observed to limit their junior nestlings from eating food, either by aggression or physical interference. Experimental feeding tests revealed that heavier nestlings handled prey items more efficiently and ate food at a higher speed. The high degree of tolerance shown by senior nestlings is unusual among birds with similar ecological and phylogenetic affinities, such as herons. Tolerance by seniors cannot be easily explained by absence of parental favouritism or proximate factors known to affect the occurrence of sibling aggression in other species (rate of food transfer, brood size, hatching asynchrony or length of nestling period).

具有结构化家庭关系的晚成雏鸟（Altricial nestlings）会展现出多样化的食物争夺行为策略，涵盖从信号介导的争抢至攻击性干扰等多种形式。白鹳的亲代杀婴行为发生率处于中等偏高水平。有假说提出，这种特殊行为是亲代的适应性响应，用以应对雏鸟缺乏高效的育雏淘汰机制——即雏鸟无法通过攻击性或直接肢体干扰实现同胞淘汰。为验证这一假设，我们分析了雏鸟发育前半阶段的32个巢群的41次完整取食事件录像；该阶段恰为雏鸟完成90%生长发育的时期，此时雏鸟死亡率与体型不对称程度均达到峰值。亲代通过在巢底反吐食物的方式，同时向所有雏鸟投喂食物，未观测到任何亲鸟与雏鸟间的喙对喙直接喂食行为。本研究未观察到优势雏鸟通过攻击性或肢体干扰的方式阻碍弱势雏鸟取食。喂食实验显示，体重更大的雏鸟处理猎物的效率更高，进食速度也更快。优势雏鸟所展现出的高度容忍性，在具有相似生态与系统发育亲缘关系的鸟类（如鹭类）中实属罕见。而优势雏鸟的这种容忍行为，无法通过"亲本偏心缺失"，或是已知会影响其他物种同胞攻击行为发生的近因因素（食物传递速率、巢群大小、孵化异步性或雏鸟期时长）来轻易解释。