Abstract

Conflicts are inherent to family systems and may occur at three levels. First, each parent benefits if its mate takes the greater share of parental investment. Second, offspring try to manipulate their parents into devolving more resources than it is optimal for them. Third, siblings compete for resources. Food availability can affect the dynamics of each level of interaction. By means of a food supplementation experiment, we assessed how the initial availability of extra food during breeding affects later parental effort, sibling competition, and parent-offspring interactions in a small dimorphic raptor, the lesser kestrel (Falco naumanni). Being the larger sex, female nestlings are likely to have higher energy requirements. Female-biased broods had a higher rate of aggressive interactions and were fed more frequently in control nests. Food was not shared evenly among broodmates, and daughters tended to receive more feedings than sons. In young broods, parents controlled food allocation by entering the nest, whereas in older broods, offspring controlled food allocation by monopolizing the nest site entrance. Extra food induced male parents to reduce the rate of feedings delivered by entering the nest. Additionally, extra food improved nestling growth in male-biased broods, leading to an increase in the frequency of parental feedings and aggressive interactions, likely due to faster growth rates. These findings reveal a key effect of brood sex ratio in determining family interactions in a species with reverse sexual size dimorphism and suggest that all levels of conflict between family members should be considered simultaneously when investigating the evolution of parental care.

Significance statement

Breeding poses energetic costs on parents, and environmental resources are usually limited. To successfully breed, parents coordinate their efforts and manage the allocation of resources to offspring, while offspring communicate their needs. Conflict can arise among family members: each parent benefits if the other takes on most of the workload, offspring ask for more care than what parents can provide, and siblings compete for food. Food availability affects these interaction levels separately, but they have rarely been integrated. By providing extra food to lesser kestrel (Falco naumanni) nests, we show that parental provisioning behaviour and sibling competition are simultaneously affected by initial resource availability during breeding. Although lesser kestrel nestlings show only moderate sex differences in body size (and therefore energy requirements), the effect of extra food on family interactions primarily depended on the sex ratio of the brood.

中文翻译：

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育雏性别比调节性双态猛禽中额外食物对父母努力和兄弟姐妹竞争的影响

摘要

冲突是家庭系统固有的，可能在三个层次上发生。首先，如果父母一方的配偶获得了更大比例的父母投资，那么他们将从中受益。其次，后代试图操纵他们的父母投入更多的资源而不是对他们而言最合适的资源。第三，兄弟姐妹争夺资源。食物的供应量会影响每个互动层次的动态。通过食物补充实验，我们评估了繁殖过程中额外食物的初始供应量如何影响小型双形猛禽“红est”（Falco naumanni）的后期父母努力，兄弟姐妹竞争以及父母与子女的相互作用。）。作为较大的性别，雌性雏鸟可能需要更高的能量需求。女性偏爱的亲本具有较高的侵略性互动率，并且在控制巢中的喂养频率更高。兄弟姐妹之间的食物分配不均，女儿的供养往往要比儿子多。在年轻的育雏中，父母通过进入巢来控制食物分配，而在较老的育雏中，后代通过垄断产地入口来控制食物分配。额外的食物诱使雄性父母减少进入巢穴的喂养率。此外，额外的食物改善了雄性有亲育雏的雏鸟生长，这可能是由于更快的生长速度导致了父母喂养和积极互动的频率增加。

重要性声明

育种给父母带来了高昂的代价，而且环境资源通常很有限。为了成功繁殖，父母要协调努力并管理对后代的资源分配，而后代则要传达他们的需求。家庭成员之间可能会发生冲突：如果父母双方共同承担大部分工作量，则父母双方都会从中受益，后代要求的照顾要超出父母所能提供的，而兄弟姐妹则争夺食物。粮食供应量会分别影响这些相互作用水平，但很少将其整合。通过向小红k（Falco naumanni）的巢穴提供额外的食物，我们证明了父母的供给行为和兄弟姐妹竞争是同时发生的受育种期间初始资源可用性的影响。尽管较少的茶est雏鸟在体重上仅表现出中等的性别差异（因此也需要能量），但额外食物对家庭互动的影响主要取决于育雏的性别比例。