Data from: 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. The data package contains two datasets: - This data file was used to analyse the likelihood, duration and intensity of nestling begging responses to familiar versus unfamiliar odour stimuli, while controlling for several additional predictor variables. - This data file was used to analyse the effect of the olfactory discrimination test trials on nestling mass and survival as observed on day 15 after hatching