Behav Ecol. 2025 May 25;36(4). doi: 10.1093/beheco/araf058. eCollection 2025 May 22.
Birds differ in their parent-offspring interactions, and these differences may be caused by environmental variation. When food is plentiful, the chicks that are begging the most are fed the most. When food is scarce, parents instead feed the largest offspring. This change could due to offspring adjusting their behaviour, or to confounding factors not directly related to current food availability, such as brood size. Alternatively, it could equally be due to parents responding to signals differently based on their experience of food availability in the recent past, for example, over the past weeks. We tested between these competing explanations experimentally, by manipulating food availability in a population of wild great tits, . We then standardised food availability, and manipulated offspring size and behaviour by creating mixed cross-fostered broods just before filming. This isolated the effect of parental strategies while holding food availability, offspring begging and size constant across treatments, but with sufficient variation within broods to generate usable information for parents. We found that when parents had experienced plentiful, supplemented food prior to filming, they were: (1) more likely to preferentially feed the chicks that were begging the most; and (2) less likely to preferentially feed larger chicks. Chicks, on the other hand, did not differ in their behavior in relation to the environmental conditions they had experienced previously, but instead begged in relation to their immediate feeding history and their nestmates' begging intensity. Overall, our results suggest that parents have more control over food distribution than suggested by scramble competition models, and that they can flexibly adjust how they respond to both offspring signals and cues of offspring quality in response to food availability. Consequently, different signalling systems are favoured depending on environmental conditions and predictability and parental plasticity.
鸟类在亲子互动方面存在差异，这些差异可能是由环境变化引起的。当食物充足时，乞食最多的雏鸟得到的喂食也最多。当食物稀缺时，父母反而会喂养体型最大的后代。这种变化可能是由于后代调整了它们的行为，或者是由于与当前食物供应无直接关系的混杂因素，比如窝雏数。或者，这同样可能是由于父母根据它们近期（例如过去几周）对食物供应的经验，对信号做出了不同的反应。我们通过在一群野生大山雀中操纵食物供应，对这些相互竞争的解释进行了实验测试。然后我们使食物供应标准化，并在拍摄前通过创建混合交叉寄养窝雏来操纵后代的体型和行为。这隔离了亲代策略的影响，同时在各处理组中保持食物供应、后代乞食行为和体型不变，但在窝雏内有足够的差异，以便为父母提供可用信息。我们发现，当父母在拍摄前经历了充足的补充食物时，它们：（1）更有可能优先喂养乞食最多的雏鸟；（2）不太可能优先喂养体型较大的雏鸟。另一方面，雏鸟的行为与其之前经历的环境条件无关，而是根据它们近期的喂食历史和同窝雏鸟的乞食强度进行乞食。总体而言，我们的结果表明，父母对食物分配的控制比争夺竞争模型所表明的更强，并且它们可以根据食物供应情况灵活调整对后代信号和后代质量线索的反应方式。因此，根据环境条件、可预测性和亲代可塑性，不同的信号系统会受到青睐。
