Eurypygidae – Sunbittern

The Sunbittern is a bittern-like bird of tropical regions of the Americas, and the sole member of the family Eurypygidae and genus Eurypyga. It ranges from Guatemala to southern Peru, showing three extant subspecies.

Male and female adult sunbitterns have can be differentiated by small differences in the feather patterns of the throat and head. Like some other birds, the Sunbittern has powder down. Its range extends from Guatemala to Brazil, in the humid Neotropical forests, generally with an open under-storey and near rivers and streams. The species may also be present in southern Mexico as it has been traditionally reported from the Atlantic slope of Chiapas. However, no specimens are known, nor are there any recent records of sightings.

The Sunbittern is not migratory and is usually found foraging on the ground scratching for insects. They are normally cryptic, but give a spectacular display, opening their large wings and exhibiting a pattern that resemble eyes, when they feel threatened. They start nesting in the early wet season and before starting they make flight displays of 10m to 15m high in the forest canopy. They build open nests in trees laying two eggs with have blotched markings. The young are precocial, but remain in the nest for several weeks after hatching.

Sunbittern Eurypyga helias – ©Dubi Shapiro

Sunbitterns aren’t just great birds in their own right, they are also of great taxonomic and bio-geographical interest. It is the single member of its family, the Eurypigidae It’s only rather distant living relative appears to be the Kagu of New Caledonia, the sole member of the family Rhynochetidae. These two families used to be included in a heterogenous collection of birds in the Gruiformes (Cranes), but recent DNA studies (Hackett et al 2008) have led to their elevation to their own two family, two-species order the Eurypigiformes. This makes them very distinguished – the other 40 or so orders of birds contain about 10,000 species.

The traditional bio-geographical explanation for this is that both species had a Gondwana ancestor that existed on New Caledonia when it separated from Gondwana 80 million years ago. Recent studies (Grandcolas et al 2008) indicate that New Caledonia has probably been completely submerged since then and all terrestrial plants and animals have colonised it in the past 37 million years. If this is correct, then either the simple Sun Bittern – Kagu relationship is incorrect or their ancestors found some other way to get to where they are now, such as island hopping with extinctions obliterating their tracks. The mystery remains.