Patterns of vocal activity may involve information about vocalizations themselves as well as their function. In birds, vocal activity at the individual and population level is generally closely associated with breeding cycles, reaching the peak during territorial and mating competition, and decreasing with the onset of egg incubation and chick feeding. However, little is known about patterns of vocal activity in avian brood parasites that have unusual breeding cycles without parental care. Using passive acoustic monitoring, we determined the seasonal and diurnal patterns of population vocal activity in two avian brood parasites: the Common Cuckoo Cuculus canorus and the Lesser Cuckoo C. poliocephalus. We found that both species and both sexes showed a similarly highly structured pattern of seasonal vocal activity, reaching a sharp peak in the early breeding season when birds compete for territories and mates, although males sang more frequently than females. Likewise, the diurnal patterns of vocal activity were similar in both species and both sexes of cuckoos, with peak activity occurring around dawn. Nocturnal calls by male cuckoos were also detected in both species, but only in the early breeding season. Collectively, the observed patterns of population vocal activity may suggest that the absence of parental care may not extend the period of vocal activity in these two species of brood parasites.

Background: Avian brood parasitism is a breeding strategy in which brood parasites lay their eggs in the nest of other species. This behavior is closely related to aspects of the biological evolution of the parasitic species such as reduced female body size and plumage color polymorphism. However, not much is known whether it is associated with the evolution of vocalization. Methods:We collected samples of the typical male calls of 67 species belonging to the sub-family Cuculinae. Using the calls, we measured five acoustic parameters for each samples to test the differences in vocal structures between parasitic and nonparasitic species. To control for potential phylogenetic effects, we also performed phylogenetic independent contrast analyses. Results:We found that vocal structures were relatively similar among the parasitic species with a tendency to simple and low-frequency calls. In addition, harmonic structures were observed more frequently in the nonparasitic group. Conclusions:Overall, these results support the idea that brood parasitic behavior with associated ecological conditions may play a role in vocal evolution, a better understanding of which may greatly improve our knowledge of vocal diversification in non-oscine birds.

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In a parasite species, the dispersal of individuals should be dependent on the host species to which they are specialized; thus, any sexual/individual difference in host specificity may influence their dispersal patterns and, hence, population genetic structures. However, such predictions remain poorly verified in generalist avian brood parasites that are composed of multiple lineages of host-specific races. Here, we show the dispersal consequences inferred from spatial genetic structures and their association with host specificity in brood parasitic common cuckoos Cuculus canorus in which female-specific host race formation has been widely accepted. Genetic sampling from adult cuckoos confirmed restricted dispersal in both sexes and resultant genetic structures between populations where different host species breed allopatrically, whereas it was not the case between distant areas inhabited by the same host species. Contrary to the female host race hypothesis, our results demonstrate that male cuckoos may also have host specificity and disperse accordingly, conclusively allowing us to hypothesize the formation of a host race including both sexes.

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