Great spotted cuckoos disregard information on conspecific breeding success while parasitizing magpie hosts

The study of mechanisms underlying host selection by brood parasites usually lays on selection by parasites of host traits that inform on host parental abilities or location. However, brood parasites might use information extracted from past reproductive performance of either their hosts or themselves, a possibility almost neglected. In this study, we use a long-term data set to analyze whether the probability of parasitism by great spotted cuckoos (Clamator glandarius) of a magpie (Pica pica) nest in a given year is related with the reproductive outcome of any of the 2 species in the surroundings of that nest the previous year. We found that probability of parasitism for a nest in a year was explained by previous year cuckoo reproductive outcome and parasitism rate in the area surrounding the focal nest, but not by host reproductive outcome. To discern between the effect of parasitism rate and that of parasite reproductive success on parasite choices, we carried out an experiment modifying the natural correlation found between parasitism status and host and parasite success in the patches. The results showed that neither host nor cuckoo reproductive outcome in a patch after the experiment explained probability of parasitism in the following year. Only parasitism rate in the surroundings of a nest before the experiment explained probability of parasitism for this nest in the following year. Hence, these results indicate that great spotted cuckoos disregard social information related to past parasitism outcome, probably because parasitism outcome is tightly correlated with parasitism itself.