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).晚成雏鸟（altricial nestling）在结构化的巢群家庭中，会演化出多样的行为策略以争夺食物，涵盖从信号式争抢至攻击性干扰的多种形式。白鹳的子代弑亲（filial infanticide）率处于中等偏高水平。已有假说提出，该非典型行为是亲代的适应性响应，用以弥补雏鸟缺乏高效窝雏数调控机制（即通过攻击或直接物理干扰实现的窝雏减少）的不足。为验证这一假设，我们分析了育雏期前半段的32个巢群的41次完整喂食记录视频——此阶段雏鸟完成90%的生长发育，且雏鸟死亡率与体型不对称性均达到峰值。亲代通过在巢底反刍的方式，同时向所有雏鸟投喂食物，未观测到任何喙对喙（bill to bill）的直接喂食行为。研究未发现年长雏鸟通过攻击或物理干扰的方式限制年幼雏鸟取食。喂食实验结果显示，体重更大的雏鸟处理猎物的效率更高，取食速度也更快。在具有相似生态位与系统发育亲缘关系的鸟类（如鹭类）中，年长雏鸟所展现出的高宽容度并不常见。现有已知的、会影响其他物种同胞攻击行为发生的近因因素（如食物传递速率、窝雏数、孵化异步性以及育雏期长度），以及亲本偏爱缺失的情况，均无法轻易解释该宽容行为的成因。