Sunbittern

About the sunbittern

The sunbittern is a bittern-like bird of tropical regions of the Americas and the sole member of its family, Eurypygidae, and its genus, Eurypyga. It ranges from Guatemala to Brazil and includes three recognized subspecies. Molecular and morphological studies show the sunbittern is most closely related to the kagu of New Caledonia, a relationship that points to a shared Gondwanan origin; the two species together form the clade Eurypygiformes and even share a similar wing display. An indeterminate fossil relative has been found in the Green River Formation of Wyoming, suggesting the group once ranged much farther north than it does today.

The three subspecies are separated by plumage and size and do not overlap geographically. E. h. helias, the Amazonian sunbittern, lives east of the Andes across the Orinoco basin, the Amazon basin, and the Pantanal. E. h. meridionalis, the foothill sunbittern, has a narrower range along the East Andean slope in south-central Peru, at altitudes of 800 to 1,830 m (2,620–6,000 ft). E. h. major, the northern sunbittern, is found from southern Guatemala through Central America and the Chocó to western Ecuador, and may occur in southern Mexico, though no recent specimens confirm this.

The sunbittern has a generally subdued plumage of fine black, grey, and brown patterns, a long, pointed bill that is black above, and a short hallux similar to that of shorebirds and rails. Its most striking feature is hidden until the wings open: the flight feathers carry vividly colored middle webs that form bright red, yellow, and black eyespots when the wings are fully spread. These are used in courtship and threat displays toward other sunbitterns, and to startle potential predators. Males and females look similar, distinguished only by small differences in throat and head feather patterns. Like the kagu and the mesites, the sunbittern has powder down. Birds in the South American lowland subspecies have mainly brown upperparts with orange-yellow legs and lower mandible, while the other two subspecies are greyer above with sometimes redder legs and bills.

Behavior and diet

Sunbitterns are cryptic birds that rely on their subdued coloring to stay hidden, flashing their eyespot-patterned wings only when they feel threatened. Their diet covers a wide range of animal prey. Insects make up an important share, including cockroaches, dragonfly larvae, flies, katydids, water beetles, and moths, while other invertebrate prey includes crabs, spiders, shrimp, and earthworms. They also take vertebrate prey such as fish, tadpoles, toads and frogs, eels, and lizards.

Sunbitterns are among just 12 bird species across five families documented using bait or lures to draw prey within striking range, a behavior that counts as a form of tool use — though in sunbitterns this has so far only been observed in captive birds.

Sunbitterns begin nesting in the early wet season, and before nesting starts they perform flight displays 10 to 15 m (33–49 ft) high in the forest canopy. They build open nests in trees and lay two eggs marked with blotches. The young are precocial at hatching but remain in the nest for several weeks afterward.

Range and habitat

The sunbittern's range stretches from Guatemala south to Brazil, split among three subspecies with distinct, non-overlapping distributions. The nominate Amazonian subspecies occupies lowland tropical South America east of the Andes, spanning the Orinoco basin, the Amazon basin, and the Pantanal. The foothill subspecies is restricted to the East Andean slope of south-central Peru at subtropical elevations up to about 1,830 m, while the northern subspecies ranges from southern Guatemala through Central America and the Chocó region to western Ecuador. Across its range, the species favors humid Neotropical forest with an open understory, typically near rivers, streams, ponds, or lagoons.

Conservation status

The sunbittern is classified as Least Concern. No specific threats or conservation programs for the species are documented here.