Boat-billed Heron Cochlearius cochlearius Scientific name definitions

Superficially resembling night-herons in the genus Nycticorax, the Boat-billed Heron differs in its extremely wide, flat bill whose maxilla looks like the upturned keel of a boat, giving this species its common name. The only member of the genus Cochlearius, the Boat-billed Heron used to be in its own family before being grouped back into the family Ardeidae with the other herons. A crepuscular species, it uses its unique bill to hunt amphibians, small fish, crustaceans, insects, and small vertebrates, while wading through shallow water. The courtship display of this species is quite ritualized and includes carefully coordinated bill-touching and false fighting. It has been known to nest individually or in mixed species colonies of other herons and ibises. Unlike other species of herons, the Boat-billed Heron is very aggressive when defending its nest and young against potential predators, scaring away other species of birds, and vocalizing loudly, even lunging, at approaching humans.

45–53·5 cm (1 Schulenberg, T. S., D. F. Stotz, D. F. Lane, J. P. O’Neill, and T. A. Parker (2007). Birds of Peru. Princeton University Press, Princeton, NJ, USA. Close ); male 680–770 g, female 503–726 g (2 Kushlan, J. A., and J. A. Hancock (2005). The Herons. Oxford University Press, Oxford, UK. Close ). Very distinctive heron, most likely to be confused with widely sympatric Nycticorax nycticorax, but overall much whiter in appearance and has incredibly broad, flattened  and thick bill  (black with yellow wash at base), white forehead and cheeks, long black  , lanceolate crest plumes  , black upper back, buff-brown mantle, vinaceous neck-sides, with rest of upperparts grey, rich rufous underparts, and black flanks and tibial feathering; eyes dusky or brown (huge and bulging), gular pouch variably dusky sulphur-yellow, yellow and grey, or pink, and legs and feet green. Female has shorter occipital plumes. During breeding season , lining of mouth, lores and gular skin black. Juvenile has dull rufous back and wings, drab white below with buff or pinkish wash; shorter crest; does not attain full adult plumage until at least third year. Races separated on coloration and, to some extent, size: <em>cochlearius</em> palest, with pale grey upperparts and pure white breast and neck; panamensis darkest, being olive-grey above and darker lavender below, with olive-brown suffusion to face, throat and upper breast; other races generally lavender grey above, buffy brown on throat and breast, with phillipsi being the largest, ridgwayi slightly larger than zeledoni and also darker below (but paler than panamensis), while ridgwayi and panamensis perhaps intergrade in W Costa Rica.

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Editor's Note: Additional distribution information for this taxon can be found in the 'Subspecies' article above. In the future we will develop a range-wide distribution article.

Mangroves and other kinds of dense forest along coastal rivers , margins of freshwater creeks, lakes, marshes and swamps. Generally found below 650 m, but see Movements.

Basically sedentary. Mainly recorded during dry season at some well-inventoried localities in Amazonia, but this may better reflect the difficulties of adequately surveying for the species in the wet season, rather than be taken as evidence for movements (3 Lees, A. C., K. J. Zimmer, C. A. Marantz, A. Whittaker, B. J. W. Davis, and B. M. Whitney (2013). Alta Floresta revisited: an updated review of the avifauna of the most intensively surveyed locality in south-central Amazonia. Bulletin of the British Ornithologists' Club 133(3):178–239. Close ). Evidence of some movements, with one record, involving an exhausted immature, from W Peru (Lambayeque, Jul 2005) (4 Salazar Carrasco, T., Plenge, H. and Williams, R. (2006). Boat-billed Heron Cochlearius cochlearius in Lambayeque, western Peru. Cotinga. 26: 83. Close ), three records (none recent) in W Ecuador (5 Ridgely, R. S., and P. J. Greenfield (2001). The Birds of Ecuador. Volumes 1–2. Comstock Publishing Associates, Ithaca, New York, USA. Close ), occasional records from highlands of Atlantic Forest domain (6 Nilton da Silva, J. and Martinelli, M.M. (2011). Avifauna urbana do município de Santa Teresa, região serrana do estado do Espírito Santo, Brasil. Atualidades Ornitológicas. 163: 62–69. Close ) and concentrations in mangroves in several areas. Casual visitor to N Argentina, and also recorded in Santa Catarina (7 Rosário, L. A. (1996). As Aves em Santa Catarina. Distribuição Geográfica e Meio Ambiente. FATMA, Florianópolis, Brazil. Close ) (S Brazil), with single record (probably an immature) from S Caribbean island of Bonaire (Oct 1972) (8 Prins, T.G., Reuter, J.H., Debrot, A.O., Wattel, J. and Nijman, V. (2009). Checklist of the birds of Aruba, Curaçao and Bonaire, south Caribbean. Ardea. 97(2): 137–268. Close ). Records far above normal altitudinal range also hint at species’ capacity to wander, with records to 2600 m in Colombia (9 Fjeldså, J., and N. Krabbe (1990). Birds of the High Andes: A Manual to the Birds of the Temperate Zone of the Andes and Patagonia, South America. Zoological Museum, University of Copenhagen and Apollo Books, Copenhagen and Svendborg, Denmark. Close ) and even 3500 m in NW Venezuela (10 Sharpe, C. J., D. Ascanio-Echeverría, and G. A. Rodríguez (2001). Further range extensions and noteworthy records for Venezuelan birds. Bulletin of the British Ornithologists’ Club 121(1):50–62. Close ).

Variety of shrimps (Panaeus, Macrobrachium) (2 Kushlan, J. A., and J. A. Hancock (2005). The Herons. Oxford University Press, Oxford, UK. Close ), other crustacea, insects, amphibians and fish (Mugil, Dormitador, Centropomis, Ariidae) (2 Kushlan, J. A., and J. A. Hancock (2005). The Herons. Oxford University Press, Oxford, UK. Close ); also small mammals. In study of nestling diet in SE Mexico, small number of samples revealed that most prey were fishes 10–30  mm in length, with sheephead minnow (Cyprinodon variegatus) and gold-spotted killifish (Floridicthys carpio) the most frequent, accounting for 91% of total biomass (11 Ramo, C. and Busto, B. (1993). Resource use by herons in a Yucatan wetland during the breeding season. Wilson Bull.. 105(4): 573–586. Close ). Passive feeder, capturing most of its prey using Standing or by Walking Slowly, only occasionally employing other techniques such as Foot Stirring (12 Hilty, S. L. (2003). Birds of Venezuela. Christopher Helm, London, UK. Close ), Walking Quickly or Running (2 Kushlan, J. A., and J. A. Hancock (2005). The Herons. Oxford University Press, Oxford, UK. Close ). Form of bill may be feeding adaptation, since regularly used as scoop, in which the bill is partially submerged and thrust forwards as bird walks, a technique unparallelled in rest of Ardeidae. Generally crepuscular and nocturnal, in line with large eyes, and probably defends feeding territory, although occasionally forms aggregations (2 Kushlan, J. A., and J. A. Hancock (2005). The Herons. Oxford University Press, Oxford, UK. Close ); exceptionally feeds by day.

Vocalizes frequently, giving “an, an, an, an” or “oh, oh, an-an” in flight or when fleeing disturbance (described as chimpanzee Pan troglodytes-like) (12 Hilty, S. L. (2003). Birds of Venezuela. Christopher Helm, London, UK. Close ), but which can become longer  or shorter chanting series, the former a territorial call given in greeting at the nest and often elicting chorus of calling within colony, the latter indicating agitation; also a “ha, go, go, go, go” in threat, when foraging or when disturbed, a faint “ump” in contact, and a popping sound made by snapping the bill closed, which may be double and also used in conjunction with the “an” call (2 Kushlan, J. A., and J. A. Hancock (2005). The Herons. Oxford University Press, Oxford, UK. Close ).

Season related to rains: Jun–Jul in W Mexico; at least Mar–Jun in Honduras (13 Monroe, B. L., Jr. (1968). A Distributional Survey of the Birds of Honduras. Ornithological Monographs 7. American Ornithologists’ Union, Washington, DC, USA. Close , 2 Kushlan, J. A., and J. A. Hancock (2005). The Herons. Oxford University Press, Oxford, UK. Close ); Feb–Jul in E Costa Rica (14 Gómez, J., Gil-Delgado, J.A. and Monrós, J.S. (2006). Breeding success of a colony of Boat-billed Herons Cochlearius cochlearius (Ciconiiformes: Ardeidae) in pasturelands of Costa Rica. Rev. Biol. Trop. (Int. J. Trop. Biol.). 54(4): 1131–1134. Close ); Jun–Sept in N Venezuela (12 Hilty, S. L. (2003). Birds of Venezuela. Christopher Helm, London, UK. Close ); Jun–Oct in Trinidad; Aug in Surinam (2 Kushlan, J. A., and J. A. Hancock (2005). The Herons. Oxford University Press, Oxford, UK. Close ); Nov in Brazil; in Veracruz, Campeche and Quintana Roo (Mexico) and tidal zones of Panama, where aquatic habitats persist during dry season, nesting recorded Jan–Apr (15 Lopez-Ornat, A. and Ramo, C. (1992). Colonial waterbird populations in the Sian Ka’an Biosphere Reserve (Quintana Roo, Mexico). Wilson Bull.. 104(3): 501–515. Close ). Solitary or in small groups of 5–12 pairs (2 Kushlan, J. A., and J. A. Hancock (2005). The Herons. Oxford University Press, Oxford, UK. Close ), sometimes in mixed colonies with Nycticorax nycticorax (13 Monroe, B. L., Jr. (1968). A Distributional Survey of the Birds of Honduras. Ornithological Monographs 7. American Ornithologists’ Union, Washington, DC, USA. Close ), Butorides striata (2 Kushlan, J. A., and J. A. Hancock (2005). The Herons. Oxford University Press, Oxford, UK. Close ) or Scarlet Ibis (Eudocimus ruber) (16 Sick, H. (1997). Ornitologia Brasileira. Editora Nova Fronteira, Rio de Janeiro, Brazil. Close ). Activity at colony not always synchronous, e.g. in Honduras, some birds were still laying when most nests had young on point of fledging (13 Monroe, B. L., Jr. (1968). A Distributional Survey of the Birds of Honduras. Ornithological Monographs 7. American Ornithologists’ Union, Washington, DC, USA. Close ). Nests in mangroves or other densely-foliated trees (e.g. Mangifera indica) (14 Gómez, J., Gil-Delgado, J.A. and Monrós, J.S. (2006). Breeding success of a colony of Boat-billed Herons Cochlearius cochlearius (Ciconiiformes: Ardeidae) in pasturelands of Costa Rica. Rev. Biol. Trop. (Int. J. Trop. Biol.). 54(4): 1131–1134. Close ), 0·4–10 m above ground or water; flat stick nest (300–350 mm wide by 100–150 mm thick) (2 Kushlan, J. A., and J. A. Hancock (2005). The Herons. Oxford University Press, Oxford, UK. Close ) sometimes with fresh, leafy branches; nest  fairly small, but can grow large if used repeatedly over years (55% of structures were reused in one study) (2 Kushlan, J. A., and J. A. Hancock (2005). The Herons. Oxford University Press, Oxford, UK. Close ); nests of other species sometimes used. Can lay both second or replacement clutches, although these are typically smaller, e.g. in Costa Rica, three eggs more common in first clutches (90%, n = 10; mean 2·9 eggs), whereas two eggs predominated in second attempts (73%, n = 15; mean 2·3 eggs) (14 Gómez, J., Gil-Delgado, J.A. and Monrós, J.S. (2006). Breeding success of a colony of Boat-billed Herons Cochlearius cochlearius (Ciconiiformes: Ardeidae) in pasturelands of Costa Rica. Rev. Biol. Trop. (Int. J. Trop. Biol.). 54(4): 1131–1134. Close ). Clutch 1–4 (typically three) pale blue to green eggs, often spotted with cinnamon at larger end, mean size 49·5 mm × 33 mm in Mexico, 49·7 mm × 35·9 mm on Trinidad and 50·3 mm × 35·3 mm in Surinam (2 Kushlan, J. A., and J. A. Hancock (2005). The Herons. Oxford University Press, Oxford, UK. Close ); incubation 23–28 days, by both adults, commencing with first egg (2 Kushlan, J. A., and J. A. Hancock (2005). The Herons. Oxford University Press, Oxford, UK. Close ); chicks have thick, pale grey down , dull white below, with blackish crown (but no crest), and are fed mainly at night (2 Kushlan, J. A., and J. A. Hancock (2005). The Herons. Oxford University Press, Oxford, UK. Close ); fledging period unknown. Data on nesting success incomplete, but inferred to be low, with success similar for first and second clutches in Costa (20·7% and 21·7%, respectively), although in both cases earlier clutches tended to survive better, while starvation and bad weather which destroyed nests were main causes of failure (14 Gómez, J., Gil-Delgado, J.A. and Monrós, J.S. (2006). Breeding success of a colony of Boat-billed Herons Cochlearius cochlearius (Ciconiiformes: Ardeidae) in pasturelands of Costa Rica. Rev. Biol. Trop. (Int. J. Trop. Biol.). 54(4): 1131–1134. Close ), although elsewhere human disturbance and predation have been considered main threats, and perhaps also suffers some predation from grackles (Quiscalus) (2 Kushlan, J. A., and J. A. Hancock (2005). The Herons. Oxford University Press, Oxford, UK. Close ). Five young successfully fledged from two nests, both with three eggs, in Jalisco (W Mexico), the other egg being infertile (17 Cupul-Magaña, F.G. (2004). Observaciones sobre la anidación de tres especies de ardeidos en el estero Boca Negra, Jalisco, México. Huitzil. 5(1): 7–11. Close ).

Not globally threatened (Least Concern). Widespread, generally found in all suitable habitat within range; no details available on true status and population sizes. Common breeder in parts of Mexico, e.g. Marismas Nacionales, delta of R San Pedro; 300 pairs counted on SW coast of Oaxaca. In Palo Verde National Park, Costa Rica, population estimated at 210 pairs in early 1980s; maximum 400 birds counted by Crooked Tree Lagoon, in Belize ; common breeder in Nicaragua, but considered uncommon in Panama (2 Kushlan, J. A., and J. A. Hancock (2005). The Herons. Oxford University Press, Oxford, UK. Close ). Locally common in Venezuelan llanos (12 Hilty, S. L. (2003). Birds of Venezuela. Christopher Helm, London, UK. Close ). Estimated few thousand pairs in Surinam; local in Colombia and rare on Trinidad (absent Tobago) (18 Kenefick, M., Restall, R. and Hayes, F.E. (2011). Birds of Trinidad & Tobago. Second edn. Christopher Helm, London. Close ).