Nest illumination and the evolution of egg rejection in hosts of brood parasites

Hosts of avian brood parasites, such as cuckoos, are duped into taking care of a foreign chick and this has led to the evolution of host defenses, such as egg rejection. However, many host species are not egg rejecters and it has been suggested that poor illumination inside closed nests may constrain the evolution of this defense. In this study, we experimentally increased the light inside the dome nests of Yellow-Rumped Thornbills, the main host of the Shining Bronze-Cuckoo. Our results show that rejection events did not increase significantly when nests were brighter, although there is a possibility that rejection mistakes could decrease. Moreover, we found that natural light levels inside dome nests were highly variable, and in many cases as high as those in cup-nesting species with high rejection rates. This evidence suggests that rapid changes in nest illumination do not alter rejection behavior.