Head size does not predict egg-rejection behavior in Daurian redstarts (Phoenicurus auroreus)

Avian brood parasites impost heavy costs on their hosts, which is expected to select for hosts having a bigger brain to do better in egg-rejection behavior, a process that typically involves cognitive skills. Daurian redstarts (Phoenicurus auroreus), a common host of common cuckoos (Cuculus canorus), defend against brood parasitism mainly by rejecting the parasitic egg from the nest, but with a large between-individual variation.

In this study, we tested whether hosts’ head size (proxy for brain size) positively correlates with egg-rejection behavior in Daurian redstarts. However, we found that the head size of redstart females that recognized the model egg was similar to that of individuals that did not recognize the egg. Moreover, females that ejected the model egg did not possess a bigger head than individuals that accepted the egg.