Genetic relatedness of communally breeding guira cuckoos

Abstract. A population of sexually monomorphic, communally breeding guira cuckoos, Guira guira, located near Brasilia, Brazil, was studied during three breeding seasons. Previous studies indicated considerable reproductive conflict among adults over contribution to the incubated clutch. In this study parentage and relatedness among nestlings were evaluated by DNA fingerprinting of samples from four nesting groups. The hypotheses tested were: (1) that guira cuckoo breeding groups consisted of monogamous pairs: and (2) that a single female contributed most of the incubated eggs in each group. The data indicate that nestmates were offspring of different adults. Some adults did not breed. The monogamy hypothesis was not supported by the data. Most related nestlings (78%) appeared to be half-, but not full-siblings. Parentage analyses directly suggested polygynandry in one breeding group and polygamy in another. Only 41% of pairs of nestlings selected at random from the same nest were found to share statistically significant numbers of bands. A single female was not responsible for the majority of young in a nest; however, further research is necessary to evaluate the possibility that dominant females contribute more incubated eggs than do subordinates. The data exemplify a breeding system in which nestling rivalries and reproductive conflict among adults would be expected.