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The solitary species in this exclusively New World family of waterbirds is found in Paraguay. Considered closest to waders or herons by the earliest taxonomists, osteologically and pterylographically it recalls the Old World Cranes (Gruidae), whilst the digestive system is Rail-like. Recent DNA-DNA hybridisation analysis has even placed it within the Heliornithidae! It is suspected to have diverged from the Cranes in the late Paleocene. The earliest fossils date back 54 million years ago, but the surviving species first appears in the Pleistocene.
Superficially it looks like a large, heavyset ibis with an erect stance. The neck and bill are long, the latter laterally-compressed and slightly decurved, taking a sudden abrupt bend to the right close to the tip. Tip of the lower mandible is twisted horizontally and sharpened against the tip of the maxilla, an adaptation for removing snails from their shells. The tongue reaches the end of the bill and splits into horny filaments at the tip. The wings are broad and rounded with 26 remiges. There are 10 primaries, the outermost narrowed and sickle-shaped and capable of producing a winnowing sound in territorial flight (though normal flight is silent). Tail short and broad with 12 rounded retrices. Legs are long with bare tarsi, the toes being long and slender and claws long and sharp, allowing them to walk on floating vegetation and perch in trees. They fly strongly, the legs dangling in short flights, but trailing behind the tail in longer flights. The wing beats are deep and steady with a flick on the upward stroke. In flight the neck is held outstretched but slightly below the horizontal giving a hump-backed appearance. Upon landing the bird pitches abruptly downwards and may scamper into cover. Limpkins are fast runners and the head bobs when walking. They swim infrequently, but do so strongly with wing tips and tail elevated.
Limpkins occur in aquatic habitats where water snails and freshwater mussels are plentiful. They are commonly active at night and roost in trees. The elongated trachea is looped and convoluted, increasing the volume of vocalisations of males so that they may be heard over great distances. Females are usually quiet. They forage by visual means and touch, captured snails being taken to a dry-land feeding area which result in characteristic piles of shells. The snail is placed on a solid surface and receives 1 or 2 blows from the bill until the tip can be inserted behind the operculum of the snail. The tip then snips the muscle free of the shell and the flesh is removed leaving the shell intact. 
Limpkins are territorial year-round, with territories defended by males. During courtship pairs forage together. The nest is situated on the ground or in trees, generally in areas with clear views of the surroundings. Nest building is begun by the male but the female contributes later in the process. Eggs are buffy with darker blotches towards the broader end. Both sexes incubate for a period of c27 days, the male taking the day shift and the female sitting at night. Young are nidifugous and grow fast, reaching almost adult size in 6 weeks. Both sexes feed the young. Juveniles are independent at 11 to 17 weeks. A second clutch is common.
Male larger than female. Though there are no sexual differences in plumage but the two sexes are vocally distinct. Juveniles are similar but with less conspicuous white markings.

Bryan DC
1996 - Aramidae Handbook of the Birds of the World Volume 3 - Lynx Ediciones.
Bryan DC
2002 -
Limpkin Aramus guarauna. In The Birds of North America, No. 627 (A. Poole and F. Gill, eds.). The Birds of North America, Inc., Philadelphia, PA.
Campbell B & Lack E
1985 - A Dictionary of Birds - T & AD Poyser.