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...