Great spotted cuckoos show dynamic patterns of host selection during the breeding season

Avian brood parasites depend entirely on their hosts to raise their nestlings until independence. Thus, parasite females should select suitable host nests for egg laying according to traits that enhance offspring survival. Availability of nests of certain characteristics influencing survival of parasitic offspring is however temporally dynamic and, thus, patterns of host selection should be evaluated considering characteristics of available host nests the day of parasitism. This allows detecting possible seasonal changes and, therefore, a more realistic picture of host selection by brood parasites. In this paper, we adopt such a new approach, and consider daily availability of magpie (Pica pica) host nests at different breeding stage that were or were not parasitized by the great spotted cuckoo (Clamator glandarius). Theory predicts that cuckoos should select host nests at the laying stage. Accordingly, we detected that cuckoos preferred to parasitize magpie nests at the laying stage, but, mainly those that already harboured one or two cuckoo eggs, which may seem counter-intuitive. We also showed that patterns of host selection by cuckoos varied during the breeding season, which implies that brood parasites-hosts interaction is dynamic depending on phenology. These patterns are hidden when not considering the temporally dynamic nature of availability of host nests of characteristics of interest. We discuss the importance of such patterns and considering diary hosts nests availability for detecting them.