Study species

The Hoatzin (Opisthocomus hoazin) is a relatively large bird (700–900 g, 70 cm overall length) which inhabits riparian forests and swamps in the Amazon and Orinoco river basins (Figure 5.1). As a folivorous, semi-ruminant, cooperatively breeding bird, the Hoatzin is among the most unusual of avian species. The swimming and climbing abilities and functional wing claws of the young are well known among ornithologists (e.g. Beebe 1909). The latter have remained the most recognized ‘primitive’ feature of the bird, prompting early speculation on the reptilian affinities of Opisthocomus. One author (Penard 1908, p. 309) went so far as to suggest that the Hoatzin ‘formed the transition between the birds and the creeping animals’, though numerous avian groups possess wing claws at some stage of development (Heilmann 1927). In no other group are these claws as well developed as in young Hoatzins, nor are they used for climbing or predator escape in other species.

The earliest taxonomic references to the Hoatzin are by Hernandez (1651), who presented an accurate anatomical description but confused its habitats with those of other species, erroneously stating that: