Sunbitterns (Eurypygidae)

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Sunbitterns

(Eurypygidae)

Class Aves

Order Gruiformes

Suborder Eurypygae

Family Eurypygidae

Thumbnail description
Elegant, bittern-like bird with a long bill, slender neck, and long orange legs; plumage mottled and cryptic except for spectacular sunburst pattern hidden in wings; primarily black head with white striping above and below the ruby-red eyes; sexes similar in appearance

Size
18–21 in (46–53 cm) in length; 6.3–7.8 oz (180–220 g); recorded up to 9 oz (255 g)

Number of genera, species
1 genus; 1 species

Habitat
Tropical forested riparian areas

Conservation status
Not threatened

Distribution
Central and South America

Evolution and systematics

The taxonomic placement of the sunbittern (Euypyga helias) has been a subject of debate through the years. Due to the lack of fossils with which to study, the species has been classed primarily on morphological and behavioral characteristics. It is believed to be most closely related to the kagu (Rhynocetus jubatus) of New Caledonia and both species may have originated from the Mesozoic birds of Gondwana. Egg-white protein analysis, hidden patterns in the wings, and soft, lax feathers are a few of the shared similarities. A relationship to the paintedsnipes (Rostratulidae) has also been suggested, but lacks the egg-white protein affinity shared with the kagu. Otherwise, the species seems to be most closely related to rails and bustards.

Physical characteristics

The common name is derived from the normally concealed wing markings which reveal a "sunburst" on opening. The bill is fairly straight and long, upper mandible black, and lower bright orange. The legs are also orange. The sunbittern has a long slender neck and long fan-shaped tail with two broad stripes of chestnut and black. The head is black with white stripes above and below the eyes and across the cheeks. The iris is red. Over-all plumage is cryptic, and individuals are perfectly camouflaged when in dappled sunlight due to the mottled plumage. Neck and breast are brown, upperparts chestnut, all barred with black. The throat is white, abdomen buff. In Eurypyga helias helias, the bill is more slender and the black dorsal bars of the upperparts are wider. E. helias major may be differentiated by a stouter bill and narrow black bars, whereas the Peruvian race E. helias meridionalis exhibits more red on the hindneck with narrower black bars on the rump and upper tail. Sexes are similar, although males may be slightly more colorful.

Distribution

E. helias major: Along most of the Caribbean slope of Central America, Columbia west of the Andes, south to western Ecuador.

E. helias helias: East of the Andes, through Amazonian regions of Colombia, Venezuela, and Guineas; also northern Brazil, central Ecuador, and northeastern Peru.

E. helias meridionalis: Tropical zones of South Peru.

Habitat

Forested areas with an open understory near swift-moving rocky streams. Also inhabits slower-moving creeks, river sandbars, swamps, and pond edges. Typically found at altitudes of 300–4,000 ft (100–1,200 m), but documented at 5,000 ft (1,500m). Although thought to be nonmigratory, birds that occupy territories with a long dry season may have to travel short distances to find suitable forest habitat bordering permanent water sources.

Behavior

Usually found singly or in pairs. Tends to walk with a deliberate gait, making periodic flights across deep water. If alarmed or disturbed, may fly to perch on low tree branches. Wary, but not shy.

The frontal display, a defensive response to threat or disturbance, was once believed to be a part of courtship. The wings are opened and rotated forward, exposing the usually hidden sunburst pattern. The tail is raised and fanned, while the breast is lowered and the head is pointed toward the intruder, resulting in a bird appearing much larger. The broken-wing display is similar to that employed by many other species of birds, whereby one wing is dragged along the ground in the hopes of distracting potential predators from the nest site to chase the "injured" adult.

Likely to hiss if disturbed, and this, along with swaying of the neck is commonly used as a method of defense by both adults and chicks. The song, a high, ringing whistle, is most commonly heard in early morning. The alarm call is much harsher and consists of a loud repetition of six to eight notes, similar to "ka, ka, ka…"

Feeding ecology and diet

Stalks prey deliberately, with neck retracted. Spears prey with quick jabs. Also picks and gleans in leaf litter or thick moss lining the forest floor. Typically hunts alone, slowly, and methodically. The diet is diverse including vertebrates such as small fish, tadpoles, and frogs. Invertebrates include spiders, flies, water beetles, cockroaches, katydids, dragonfly and dobsonfly larvae, snails, and crustaceans such as crabs and shrimp. Freshwater eels, toads, earthworms, and moths may also be hunted. Sunbitterns frequently wash their food before eating, and the likelihood is increased if feeding young. This likely aids in rinsing foul-tasting or noxious adherents.

Reproductive biology

The first observations of sunbittern breeding were made in 1865 in the London Zoological Garden where a captive pair raised two nestlings. Both sexes share in nest building,

incubation, and the subsequent brooding, feeding, and protection of the young.

The breeding cycle begins with the rainy season, when ample mud is available for nest-building. Courtship and pair-bonding rituals include flight displays, head-bobbing, excessive preening, begging displays, duet rattles, and numerous calls and trills. Courtship flight displays have been observed just above the tree line, 33–49 ft (10–15 m) in height.

The platform nest is a bulky, almost globular, collection of decaying leaves, mud, moss, and stems. Grass fibers and mud are used to saddle the nest to the branch. Placement varies, but is typically on a horizontal or slightly sloping branch, 1.2–3.9 in (3–10 cm) wide, and 3–23 ft (1–7 m) above ground. It may or may not have lateral support, but is always under a closed canopy and adjacent to water. Ground nesting is rare. The two to three eggs are smooth and slightly glossy, pinkish buff in color, with a scattering of purplish brown spots at the large end. Incubation lasts 27–30 days.

Hatching may be staggered, with the second chick hatching 24–48 hours after the first. Chicks are downy with open eyes and a bright pinkish orange gape. Costa Rican chicks are pale brown, marbled with black, whereas those of Venezuela are cream with black markings. Chicks are attended and brooded almost constantly during the first week, being able to stand and flap wings by day seven. Fledging occurs at approximately 30 days, the chicks leaving the nest with adult-like feathers. Observations of captive pairs indicate that both sexes are able to breed at two years of age. The adults molt after breeding.

Conservation status

Although not threatened, the race E. helias major has been listed as declining, described as very rare to local in some areas. E. helias meridionalis of Peru may be at threat due to its limited range. The species is becoming fairly common in zoo collections, negating the need to deplete wild populations. Potential

threats to populations are similar to those of many species, including loss of habitat and manipulation of waterways via damming or channeling of rivers.

Significance to humans

Young are occasionally removed from the nest and tamed by locals for their fly- and spider-catching abilities. Reported to live 25–30 years in captivity, but more commonly 15. There are no longevity records for wild birds. Hunting has been reported, but is not thought to constitute a threat due to the difficulty in finding the species and the abundance of more common game birds.

Resources

Books

Sick, H. Birds in Brazil. Princeton: Princeton University Press, 1993.

Haverschmidt, F., and G.F. Mees. The Birds of Suriname. 2nd ed. Paramaribo: Vaco, 1994.

Hilty, Steven L. Birds of Tropical America: A Watcher's Guide to Behavior, Breeding & Migration. Willowdale: Firefly, 1994.

Thomas, B.T. "Family Eurypygidae (Sunbittern)." In Handbook of the Birds of the World. Vol. 3, edited by J. del Hoyo, A. Elliott, and J. Sargatal. Barcelona: Lynx Edicions, 1996.

Howell, S.N.G., and S. Webb. A Guide to the Birds of Mexico and Northern Central America. Oxford and New York: Oxford University Press, 1995.