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.
The Sunbittern is normally found near wooded streams or creeks at elevations of up to 909 m. It hunts fish and other small vertebrates much in the same way as herons do. The bird has a generally subdued coloration, with fine linear patterns of black, grey and brown. Its remiges however have vividly-colored middle webs, which with wings fully spread show bright eyespots in red, yellow, and black. These are shown to other sunbitterns in courtship and threat displays, or used to startle potential predators. Like some other birds, the Sunbittern has powder down.
They build domed nests in trees, and lay two eggs with blotched markings. The young are precocial, but remain in the nest for several weeks after hatching.
The sunbittern is usually placed in the Gruiformes, but this was always considered preliminary. In some aspects of its morphology the Sunbittern is close to the herons and their relatives (which include bitterns), but this appears to be convergent evolution due to similar lifestyles. Altogether, the bird is most similar to another enigmatic bird provisionally placed in the Gruiformes, the Kagu. Molecular studies (e.g. Fain & Houde 2004) seem to confirm that the Kagu and Sunbittern are each other's closest living relatives. 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 possibly also includes 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.
The rather comprehensive DNA study by Hackett et al confirms that the sunbittern and the Kagu are close relatives but rather surprisingly it puts these two as a sister group of the swifts, nightjars and hummingbirds.