Ecology of the Folivorous Hoatzin (Opisthocomus hoazin) on the Venezuelan plains

The Hoatzin (Opisthocomus hoazin) is the only avian folivore known to have fermentative digestion in the crop. We compare results on nesting, growth, and feeding in Pinero Ranch, Cojedes State, Venezuela, with results from another location in the Venezuelan plains. The Hoatzin nests in trees abundant in the habitat. Nests containing two eggs were predominant. Growth rate of chicks was linear over the nesting period (5.68 g/day). The diet of the Hoatzin consisted of young leaves and twigs of some of the most abundant trees in its habitat. Although there are no reports on the phytochemistry of dietary plants, families to which these plants belong include plants known to contain secondary compounds. The crop, which functions as a mediator in plant-Hoatzin interactions and as a detoxification chamber, deserves further study. Received 4 November 1992, accepted 13 November 1993.