Do common cuckoo chicks suffer nest predation more than host nestlings?

Abstract

Nestlings of brood parasites exhibit more intensive begging than offspring of their hosts to gain sufficient amount of food or competitive advantage over host nestlings. This begging behaviour should be costly because exuberant acoustic begging may more likely attract nest predators. However, to date, nobody has explored the survival of nests with and without chicks of brood parasites in the common cuckoo (Cuculus canorus) host system. Here, we analysed an extensive dataset of 817 great reed warbler (Acrocephalus arundinaceus) and 788 reed warbler (Acrocephalus scirpaceus) nests to explore the relationships between nest predation and parasitism status (parasitized vs. non-parasitized), nest contents (cuckoo chick vs. host nestlings) and age of nestlings. We found that although parasitized nests had higher predation rate than non-parasitized nests in the incubation stage, the effect of original parasitism status almost disappeared in the nestling stage. In both host species, nests with younger cuckoo chicks survived similarly to nests with host nestlings of the same age (till the ninth day of age). Later on, however, nest contents influenced nest predation in each species differently. While nests with older cuckoo chicks (from the ninth to the 17th day of age) did not survive worse that host nestlings in the great reed warbler, older cuckoos survived much worse than host nestlings in reed warbler nests. Finally, nest survival decreased with nestling age in all three species. Thus, it seems that common cuckoo chicks can be penalized for more intensive begging only in nests of smaller reed warbler hosts. Parental feeding of young is in birds frequently accompanied by striking nestlings begging behaviour serving as a signal of their need. Brood parasites exhibit even more intense food solicitation than their hosts which may attract predators to the nest. However, this hypothesis has never been tested in a widely studied brood parasite species—the common cuckoo. Here, we analysed survival of more than 1600 nests of its two main host species. We found that nests containing older common cuckoo chicks were depredated more frequently than nests with host own nestlings only in the smaller reed warbler hosts but not in the larger and more aggressive great reed warblers. This shows that the intensity of begging could be costly in terms of nest predation at least in some common cuckoo host species.