Spotless starlings rely on public information while visiting conspecific nests: an experiment

Animals may acquire information on potential breeding sites by prospecting, which allows future optimal selection of breeding territories. The reproductive success of conspecifics, as public information (PI), has been proposed as one of the cues that prospectors could gather and then use for future reproductive decisions. We experimentally decreased brood size in spotless starling nests to investigate whether this species gathers PI while visiting conspecific nests. We expected visiting frequency to decline with the experimental decrease in brood size because visitors are expected to prefer sites with high reproductive success and to spend more time at those sites to gain familiarity. Furthermore, the effect of the experimental manipulation was recorded at three different stages of the nestling period to establish the importance of the reliability of PI. Brood size decreased in direct relation to the manipulation and, consequently, parental feeding rates decreased too. Visiting frequency of starlings to conspecific nests was affected by the interaction between the experimental manipulation and the stage in the nestling period: visiting frequency increased from decreased to control nests at the end of the nestling period, not so strongly in the middle of that period and it was not affected by the manipulation at the beginning of it. This variation in visiting frequency seemed to be better explained by brood size than by parental provisioning rate. These results may be interpreted as spotless starlings visiting conspecific nests to gather PI, which seems to increase its informative value when its reliability does.