Cochlearius cochlearius (Boat-billed Heron) can be about 51 centimeters (20 inches) tall and can weigh up to 600g. A long bushy crest, a black patch at the base of the hind neck, and a white throat and forehead, characterizes the adults. They have pale wings and tails, black wing lining and flank, a dull rusty belly, and yellow-green gular pouch and legs. The gular pouch turns black during the breeding season. Juveniles are mostly brown with buff on the chest and belly (Stiles and Skutch 1989).
These herons can be found in lowlands from Northern Mexico to Western Ecuador, Bolivia, and Northern Argentina. They roost in large groups on vegetation by wooded riverbanks, swamps, ponds and streams. During the breeding season, which goes from June through October (Costa Rica), they are found nesting in smaller colonies in similar places (Stiles and Skutch 1989; Garrigues and Dean 2007). Females lay two, sometimes three, pale blue eggs (Stiles and Skutch 1989).
The Boat-billed Heron belongs to the family Ardeidae which contains other species of herons, night herons, and egrets. All Ardeidae species, apart from the Boat-billed Heron, have long pointed bills used for spearing and snatching prey (Garrigues and Dean 2007). Boat-billed Herons were originally placed in the family Cochleariidae, which was a monotypic family containing only Boat-billed Herons, due to their unique broad bill and its’ different supporting structures. The skull of the Boat-bill Heron was later found to closely resemble that of Nycticorax nycticorax (Black-crowned Night Heron). Because of this close resemblance Boat-billed Herons were moved to the family Ardeidae (Mock 1983).
Several hypotheses have been suggested to explain why the bill is so unique in Boat-billed Herons. One hypothesis proposes that the bill can be touch-sensitive, which would allow the birds to catch fish and shrimp in the water during very dark nights. Unfortunately, anatomical analysis of the bill did not find any specialized tactile receptors. Another hypothesis speculates that opening the bill rapidly would create partial vacuum forcing water and prey into the mouth. This hypothesis also lacks empirical support. It is currently believed that this unusually broad bill probably compensates for the inaccuracy incurred during nocturnal foraging, but it might also have a sound-producing function during courtship (Mock 1983; Kushlan 2009).
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