Begging blue tit nestlings discriminate between the odour of familiar and unfamiliar conspecifics

1. Offspring often solicit, and compete for, limited parental care by elaborate begging behaviour. Kin selection theory predicts that competing offspring should modify the intensity of their begging depending on the degree of relatedness to their nest- or litter mates. 2. Empirical evidence in birds, which are a key model in the study of parent-offspring interactions, indeed indicates that a lower level of relatedness between offspring in the nest correlates with more intense begging (i.e. more ‘selfish’ behaviour). This implies that competing nestlings can recognize kin, but the mechanism underlying such discrimination is unclear. Birds have long been thought to mainly rely on visual and auditory cues in their social communication, but there is now growing evidence for the importance of olfactory cues too. 3. To assess the potential importance of olfactory cues in modulating nestling begging behaviour, we experimentally tested in a free-living bird, the blue tit Cyanistes caeruleus, if nestlings discriminate and adjust their begging behaviour depending on their familiarity with a conspecific nestling odour stimulus. 4. We found that individuals responded with longer and more intense begging bouts to an unfamiliar compared to a familiar odour stimulus. 5. Our findings provide first evidence for a role of olfaction in modulating offspring begging behaviour in a wild bird population. Although our experiment cannot differentiate between the effects of familiarity and relatedness, it raises the interesting possibility that blue tit nestlings may also discriminate between odours of kin and non-kin, and adjust their begging behaviour accordingly. This hypothesis requires further testing.

1. 子代常通过复杂的乞食行为来索取并争夺有限的亲本抚育资源。亲缘选择理论（Kin selection theory）预测，相互竞争的子代应根据其与同巢/同窝同伴的亲缘关系程度，调整自身乞食行为的强度。2. 作为亲子互动研究核心模式类群的鸟类，相关实证研究确实表明，同巢子代间亲缘关系越低，其乞食行为强度越高（即表现出更强的"自私"行为）。这意味着相互竞争的雏鸟能够识别亲缘个体，但此类识别背后的机制仍不明确。长期以来，学界认为鸟类在社会交流中主要依赖视觉与听觉信号，但如今越来越多的证据表明嗅觉信号同样至关重要。3. 为评估嗅觉信号在调控雏鸟乞食行为中的潜在作用，我们以野生鸟类蓝山雀（Cyanistes caeruleus）为研究对象开展实验，检验雏鸟是否会根据对同种雏鸟气味刺激的熟悉程度，区分并调整自身的乞食行为。4. 我们发现，相较于熟悉的气味刺激，雏鸟对陌生气味刺激会展现出时长更长、强度更高的乞食行为。5. 本研究的发现首次为野生鸟类种群中嗅觉在调控子代乞食行为中的作用提供了证据。尽管本实验无法区分熟悉度与亲缘关系的效应，但它提出了一个有趣的可能性：蓝山雀雏鸟或许也能区分亲缘与非亲缘个体的气味，并据此调整自身的乞食行为，这一假说仍需进一步验证。