Linking individual attributes and host specialization in brood parasitic cuckoos

Generalist avian brood parasites vary considerably in their degree of host specialization (e.g., number of hosts); some parasitize the nests of just a few host species, whereas others exploit more than 100 species. Several factors, including habitat range, habitat type, and geographic location, have been suggested to account for these variations. However, inter-specific differences in individual attributes, such as personality and plasticity, have rarely been considered as potential factors of such variation, despite their potential relationship to, for example, range expansion. Using cage experiments, we tested the hypothesis that parasitic species exploiting more host species may be more active and exploratory. To this end, we quantified behaviors exhibited by two Cuculus cuckoos (Common Cuckoo C. canorus and Oriental Cuckoo C. optatus) that vary greatly in their number of host species. Specifically, we evaluated exploratory behavior displayed by birds in the cage, such as the number of movements, head-turning, wing-flapping, and stepping. The Common Cuckoo, which has a higher number of host species, tended to exhibit higher levels of exploratory behaviors than the Oriental Cuckoo. Our study showed that the two cuckoo species exhibited different exploratory levels, as predicted by the differences in their number of hosts. Further studies regarding the causality between individual attributes and host specialization with improved experimental methodology would greatly enhance our understanding of the role of individual characteristics in the coevolution of avian brood parasites and their hosts.