Begging calls and mouth colouration as predictors of breeding success in blue tits

Nestlings normally exhibit a mix of traits that attract parental care, such as postural and vocal begging and carotenoid-based mouth colouration. These signals are hypothesised to be signs of nestling needs (vocal begging) and quality (mouth colouration). Therefore, we hypothesised that broods, where nestlings beg for less time and display more saturated carotenoid-based mouth colouration, would have lower nestling mortality. We tested these predictions in two wild blue tit (Cyanistes caeruleus) populations. The breeding success (here defined as the proportion of eggs that produced fledglings) was related to nestling mouth flanges' carotenoid-based colour saturation. This means that blue tits that raised nestlings with more coloured flanges had a higher within-population breeding success. Time spent in vocal begging, by contrast, was not associated with breeding success. Hence, our findings reveal that some communication signals displayed by nestlings (carotenoid-based colouration) predict breeding success, in our study mostly reflecting the proportion of eggs that hatched, while begging intensity does not, probably because the former reflects a better maternal pre-laying condition and nestling physiological status in the mid-term. Communication signals displayed by nestlings, such as carotenoid-based mouth colouration and vocal and postural begging, are hypothesised to be signs of nestling quality and needs, respectively. In broods suffering low food availability, it is thus expected that nestlings exhibit paler carotenoid-based colouration and higher levels of begging, and these broods would suffer higher mortality rates. Here, we tested these predictions in two wild populations of blue tits, and we found that nestling carotenoid-based mouth colouration indeed predicted breeding success. Time spent begging by nestlings, by contrast, was not related to breeding success.dagger image