The sunbittern (Eurypyga helias) is a bittern-like bird of tropical regions of the Americas, and the sole member of the family Eurypygidae (sometimes spelled Eurypigidae) and genus Eurypyga. It is found in Central and South America, and has three subspecies. The sunbittern shows both morphological and molecular similarities with the kagu (Rhynochetos jubatus) of New Caledonia, indicating a Gondwanan origin, both species being placed in the clade Eurypygiformes.
Taxonomy
The sunbittern was traditionally placed in the Gruiformes, but this was always considered preliminary. Altogether, the bird is most similar to another bird that was provisionally placed in the Gruiformes, the kagu (Rhynochetos jubatus). Molecular studies seem to confirm that the kagu and sunbittern are each other's closest living relatives and have a similar wing display. They are probably not Gruiformes (though the proposed Metaves are just as weakly supported). Altogether, the two species seem to form a minor Gondwanan lineage which could also include the extinct adzebills and/or the mesites, and is of unclear relation to the Gruiformes proper. Notably, the kagu and mesites also have powder down.
An indeterminate fossil eurypygid has been documented from the Green River Formation of Wyoming, USA. This specimen, known from a full skeleton, is the oldest and only known fossil of the group, and suggests that eurypygids had a much more northernly range in the past. This specimen has been figured in several studies, and was given the unofficial name "Eoeurypyga olsoni" in a 2003 dissertation, but as-of-yet remains unnamed.
The sunbittern was formerly treated as two species (E. helias and E. major), but now they are treated as a single species with considerable variation between the subspecies. The three subspecies are recognised on the basis of plumage characters and size. The three subspecies are allopatric.
E. h. helias (Pallas, 1781) – Amazonian sunbittern
E. h. major Hartlaub,...
