|Range of I. exilis Breeding range Year-round range Wintering range|
The least bittern is one of the smallest herons in the world, with perhaps only the dwarf bittern and the black-backed bittern averaging smaller in length. It can measure from 28 to 36 cm (11 to 14 in) in length, and the wingspan ranges from 41 to 46 cm (16 to 18 in). Body mass is from 51 to 102 g (1.8 to 3.6 oz), with most least bitterns weighing between 73 and 95 g (2.6 and 3.4 oz), making this perhaps the lightest of all herons. A recent manual of avian body masses cites another species in this genus, the stripe-backed bittern, as having a mean body mass slightly lower than the least bittern, which is credited with a mean mass of 86.3 g (3.04 oz).
The bird's underparts and throat are white with light brown streaks. Its face and the sides of the neck are light brown; it has yellow eyes and a yellow bill. The adult male is glossy greenish-black on the back and crown; the adult female is glossy brown on these parts. They show light brown parts on the wings in flight.
The least bittern is an elusive bird. They spend much time straddling reeds. When alarmed, the least bittern freezes in place with its bill pointing up, turns its front and both eyes toward the source of alarm, and sometimes sways to resemble wind-blown marsh vegetation. This is perhaps a predator-avoidance behaviour, since its small size makes the bittern vulnerable to many potential predators. Thanks to its habit of perching among the reeds, the least bittern can feed from the surface of water that would be too deep for the wading strategy of other herons. The least bittern and much larger and different-looking American bittern often occupy the same wetlands but may have relatively little interaction because of differences in foraging habits, preferred prey, and timing of breeding cycles. The least bittern arrives on its breeding grounds about a month after the American bittern and leaves one or two months earlier. John James Audubon noted that a young captive least bittern was able to walk with ease between two books standing 4 cm (1.6 in) apart. When dead, the bird's body measured 5.7 cm (2.2 in) across, indicating that it could compress its breadth to an extraordinary degree.
These birds nest in large marshes with dense vegetation from southern Canada to northern Argentina. The nest is a well-concealed platform built from cattails and other marsh vegetation. The female lays four or five eggs, in extreme cases from two to seven. The eggs are pale blue or green. Both parents feed the young by regurgitating food. A second brood is often produced in a season.
These birds migrate from the northern parts of their range in winter for the southernmost coasts of the United States and areas further south, travelling at night.
They mainly eat fish, frogs, crustaceans and insects, which they capture with quick jabs of their bill while climbing through marsh plants.
The numbers of these birds have declined in some areas due to loss of habitat. They are still fairly common but are more often heard than seen. They prefer to escape on foot and hide than to take flight. These birds make cooing and clucking sounds, usually in early morning or near dusk.
Taxonomy and nomenclature
- I. e. exilis (Gmelin, JF, 1789): in north and Central America and the Caribbean
- I. e. pullus van Rossem, 1930: in north-west Mexico
- I. e. erythromelas (Vieillot, 1817): in eastern Panama and around eastern coasts of South America south to Paraguay
- I. e. bogotensis Chapman, 1914: in Colombia
- I. e. peruvianus Bond, 1955: in Peru
Birds from Ecuador are sometimes assigned to a sixth subspecies, I. e. limoncochae Norton, DW, 1965. North American birds were formerly divided into two subspecies, eastern (I. e. exilis) and western (I. e. hesperis), but this is no longer believed to be a valid distinction.
Cory's least bittern
A dark rufous morph, I. e. neoxenus, termed "Cory's bittern" or "Cory's least bittern" was originally described by Charles Cory as a separate species in 1885 from a specimen collected on or near the Caloosahatchee River, near Lake Okeechobee, in southwest Florida. Cory stated that the specimen was "without doubt perfectly distinct from any other known species". Further specimens followed over the next decades from Florida, Michigan, Illinois, Wisconsin, Ohio, and Ontario.
Initially, Cory's least bittern was accepted as a valid species, with Elliott Coues and Richard Bowdler Sharpe both including it in published species lists. As early as 1892, however, doubts were raised about the validity of Cory's least bittern as a separate species. Nonetheless, in 1896 Frank Chapman wrote a detailed paper supporting its retention as a valid species. Outram Bangs later argued, in 1915, that this view was wrong and proposed that Cory's should become a junior synonym of least bittern. This view eventually prevailed, with the American Ornithologists' Union removing the species from their list of North American birds in 1923, although others held dissenting views until at least 1928.
Cory's least bittern was once fairly common, but it is now exceptionally rare, with only five sightings since 1950. More than 50% of the historical records are from the Toronto region of Ontario. Initially known only from the North American subspecies exilis, it was first recorded in the South America subspecies erthyromelas in 1967.
The bird has a large range and a large total population, and the International Union for Conservation of Nature has assessed its conservation status as being of "Least Concern". The least bittern is protected under the Migratory Bird Treaty Act of 1918.
- BirdLife International (2012). "Ixobrychus exilis". IUCN Red List of Threatened Species. Version 2013.2. International Union for Conservation of Nature. Retrieved 26 November 2013.
- del Hoyo, Josep; Elliott, Andrew; Sargatal, Jordi, eds. (1992). Handbook of the Birds of the World. Volume 1: Ostrich to Ducks. Lynx Edicions. ISBN 978-84-87334-10-8.
- "Least Bittern". HeronConservation.org. 2011-05-21. Retrieved 2013-02-21.
- CRC Handbook of Avian Body Masses, 2nd Edition by John B. Dunning Jr. (Editor). CRC Press (2008), ISBN 978-1-4200-6444-5.
- A. Martínez-Vilalta & A. Motis, Least Bittern species account in del Hoyo, Josep, Andrew Elliott and Jordi Sargatal (1992) Handbook of the Birds of the World volume 1, page 425
- Pittaway, Ron; Burke, Peter (1996). "Recognizable forms: Cory's Least Bittern" (PDF). Ontario Birds. 14 (1): 26–40.
- Gill F & D Donsker (Eds). 2014. IOC World Bird List (v 4.1). doi:10.14344/IOC.ML.4.1 www.worldbirdnames.org Accessed 8 Jun, 2014.
- Gibbs, J.P., FA. Reid, and S.M. Melvin. 1992. Least Bittern. In A. Poole, P. Stettenheim and F. Gill (editors). The Birds of North America, No. 17. The Academy of Natural Sciences, Philadelphia; and American Ornithologists' Union, Washington, D.C.
- Cory, Charles B. (April 1886). "Description of a New North American Species of Ardetta" (PDF). The Auk. 3 (2): 262. doi:10.2307/4625371.
- Cory, Charles B. (July 1886). "More News of Ardetta neoxena" (PDF). The Auk. 3 (3): 408.
- Scott, W. E. D. (April 1892). "A Description of the Adult Male of Botaurus neoxenus (Cory), with Additional Notes on the Species" (PDF). The Auk. 9 (2): 141–142. doi:10.2307/4067935.
- Eifrig, C. W. G. (January 1915). "Cory's Least Bittern in Illinois" (PDF). The Auk. 32 (1): 98–99. doi:10.2307/4071623.
- Carpenter, Charles Knapp (January 1948). "An Early Illinois Record of "Cory's Least Bittern"" (PDF). The Auk. 65 (1): 80–85. doi:10.2307/4080230.
- Cherrie, George K. (January 1896). "Ardetta neoxena from Wisconsin" (PDF). The Auk. 13 (1): 79. doi:10.2307/4068762.
- Ruthven, Alexander G. (July 1907). "Another specimen of Cory's Bittern" (PDF). The Auk. 24 (3): 338. doi:10.2307/4070385.
- Cross, W. (1892). "A new Species for Ontario". Proceeding. of the Ornithological Subsection of the Canadian Institute for 1890–91: 41.
- Brown, Hubert H.; William Brewster (October 1893). "Capture of Another Ardetta neoxena at Toronto, Ontario" (PDF). The Auk. 10 (4): 363–364. doi:10.2307/4067835.
- Fleming, J. H. (January 1902). "Cory's Bittern" (PDF). The Auk. 19 (1): 77–78. doi:10.2307/4069217.
- Ames, J. H. (1894). "Third Specimen of Ardetta neoxena taken at Toronto". The Biological Review of Ontario. 1: 52.
- Pickering, Charles; William Brodie (1894). "Fourth Specimen of Ardetta neoxena at Toronto". The Biological Review of Ontario. 1: 54.
- Chapman, Frank M. (January 1896). "The Standing of Ardetta neoxena" (PDF). The Auk. 13 (1): 11–19. doi:10.2307/4068734.
- Bangs, Outram (October 1915). "Notes on Dichromatic Herons and Hawks" (PDF). The Auk. 32 (4): 481–484. doi:10.2307/4072589.
- Stone, Witmer; Harry C. Oberholser; Jonathan Dwight; T. S. Palmer & Charles W. Richmond (July 1923). "Eighteenth Supplement to the American Ornithologists' Union Check-list of North American Birds" (PDF). The Auk. 40 (3): 513–525. doi:10.2307/4074557.
- Taverner, P. A. (April 1928). "Cory's Least Bittern" (PDF). The Auk. 45 (2): 204–205. doi:10.2307/4074769.
- The mysterious dark Least Bittern, David Sibley, 23 July 2011
- Martins Teixeira, Dante; Herculano M. F. Alvarenga (1985). "The First Recorded Cory's Bittern (lxobrychus "neoxenus") from South America" (PDF). The Auk. 102 (2): 413. doi:10.2307/4086791.
- Birds Protected by the Migratory Bird Treaty Act. fws.gov
|Wikimedia Commons has media related to Ixobrychus exilis.|
|Wikispecies has information related to Ixobrychus exilis|
- Least bittern images by Monte M. Taylor at tsuru-bird.net, © 2009
- Least Bittern at Field Guide: Birds of the World on Flickr
- Least Bittern Species Account – Cornell Lab of Ornithology
- Cory's least bittern and Cory's least bittern at Pantanal, YouTube videos
- Cory's least bittern in Royal Ontario Museum, Toronto, photographs of museum specimens
- "Least Bittern media". Internet Bird Collection.
- Least Bittern photo gallery at VIREO (Drexel University)