Reproductive Patterns and Social Organization of the Communal Guira Cuckoo (Guira guira) in Central Brazil

The communal breeding system of the Guira Cuckoo (Guira guira) was studied near Brasilia, Brazil. Guiras occurred in groups of 2 to 13 adults (mode of 6) in the 86 nests observed. Communal clutch size was correlated with group size, an indirect indication that more birds contribute to the clutch in larger groups. Clutch size varied from 4 to 20 eggs, but usually fewer eggs were incubated than were laid, since egg tossing by the adults was common. The temporal patterns of egg laying and egg loss, while generally similar to those of other crotophagines, differed in some ways. Egg losses occur at any time after laying starts. Losses may occur after several eggs have accumulated in the nest, may affect only part of the clutch, and may happen close to, or during, the hatching of chicks. Only 26% of eggs developed into fledglings; high mortality rates for eggs and chicks are due to several causes. An individual may pay a price for group membership through a lowered short-term reproductive success; however, long-term data are needed to clarify individual lifetime benefits associated with communal breeding in this species.