|Distribution map of Least Bittern
Yellow: breeding, green: year-round, blue: nonbreeding
Ardetta exilis, Ardetta neoxena, Ixobrychus exilis neoxenus, Ixobrychus neoxenus
This is one of the smallest herons in the world, with perhaps only the Dwarf Bittern and the Black-backed Bittern averaging smaller in length. This tiny bittern 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 birds between 73 and 95 g (2.6 and 3.4 oz), making this perhaps the lightest of all herons. This 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.
This Least Bittern is often 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 behavior, 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 4 or 5 eggs, in extreme cases from 2 to 7. The eggs are pale blue or green. Both parents feed the young by regurgitating food. A second brood is often produced in a season.
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 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
- exilis: in north and Central America and the Caribbean
- pullus: in northwest Mexico
- erythromelas: in eastern Panama and around eastern coasts of South America south to Paraguay
- bogotensis: in Colombia
- peruvianus: in Peru
Birds from Ecuador are sometimes assigned to a sixth subspecies, limoncochae: North American birds were formerly divided into two subspecies, eastern exilis and western hesperis, but this is no longer believed to be a valid distinction.
Cory's Least Bittern
A dark rufous morph, "neoxenus", termed "Cory's Bittern" or "Cory's Least Bittern" was originally described by 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. However, as early as 1892, 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.
- BirdLife International (2012). "Ixobrychus exilis". IUCN Red List of Threatened Species. Version 2013.1. International Union for Conservation of Nature. Retrieved 18 November 2013.
- del Hoyo, et al., Handbook of the Birds of the World. Volume 1: Ostrich to Ducks. Lynx Edicons (1992), ISBN 978-84-87334-10-8
- Least Bit. Heronconservation.org (2011-05-21). Retrieved on 2013-02-21.
- 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 and Burke, Peter (1996). "Recognizable forms: Cory's Least Bittern". Ontario Birds 14 (1): 26–40.
- 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.e.
- Cory, Charles B. (April 1886). "Description of a New North American Species of Ardetta". The Auk 3 (2): 262. doi:10.2307/4625371.
- Cory, Charles B. (July 1886). "More News of Ardetta neoxena". The Auk 3 (3): 408.
- Scott, W. E. D. (October 1889). "A Second Specimen of Cory's Bittern (Botaurus neoxenus)". The Auk 6 (4): 317–318. doi:10.2307/4066876.
- Scott, W. E. D. (April 1892). "A Description of the Adult Male of Botaurus neoxenus (Cory), with Additional Notes on the Species". The Auk 9 (2): 141–142. doi:10.2307/4067935.
- Cory, Charles B. (July 1891). "Capture of a fourth specimen of Ardetta neoxena". The Auk 8 (3): 309. doi:10.2307/4067875.
- Scott, W. E. D. (July 1891). "Notes on the Nest and Habits of Cory's Bittern". The Auk 8 (3): 309–10. doi:10.2307/4067875.
- Watkins, L. Whitney (January 1895). "Cory's Least Bittern in Michigan". The Auk 12 (1): 77. doi:10.2307/4068216.
- Taverner, P. A. (January 1905). "Description of Second Michigan Specimen of Cory's Least Bittern". The Auk 22 (1): 77–78. doi:10.2307/4069881.
- Eifrig, C. W. G. (January 1915). "Cory's Least Bittern in Illinois". The Auk 32 (1): 98–99. doi:10.2307/4071623.
- Carpenter, Charles Knapp (January 1948). "An Early Illinois Record of "Cory's Least Bittern"". The Auk 65 (1): 80–85. doi:10.2307/4080230.
- Cherrie, George K. (January 1896). "Ardetta neoxena from Wisconsin". The Auk 13 (1): 79.
- Ruthven, Alexander G. (July 1907). "Another specimen of Cory's Bittern". 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. and William Brewster (October 1893). "Capture of Another Ardetta neoxena at Toronto, Ontario". The Auk 10 (4): 363–364. doi:10.2307/4067835.
- Fleming, J. H. (January 1902). "Cory's Bittern". 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 and 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". The Auk 13 (1): 11–19. doi:10.2307/4068734.
- Bangs, Outram (October 1915). "Notes on Dichromatic Herons and Hawks". The Auk 32 (4): 481–484. doi:10.2307/4072589.
- Stone, Witmer, Harry C. Oberholser, Jonathan Dwight, T. S. Palmer, and Charles W. Richmond (July 1923). "Eighteenth Supplement to the American Ornithologists' Union Check-list of North American Birds". The Auk 40 (3): 513–525. doi:10.2307/4074557.
- Taverner, P. A. (April 1928). "Cory's Least Bittern". The Auk 45 (2): 204–205. doi:10.2307/4074769.
- The mysterious dark Least Bittern, David Sibley, 23 July 2011
- Martins Teixeira, Dante and Herculano M. F. Alvarenga (1985). "The First Recorded Cory's Bittern (lxobrychus "neoxenus") from South America". The Auk 102 (2): 413. doi:10.2307/4086791.
- BIRDS PROTECTED BY THE MIGRATORY BIRD TREATY ACT. fws.gov
- Least Bittern Images – http://tsuru-bird.net/image.htm – Copyright 2009 – Monte M. Taylor
- Field Guide on Flickr
-  – Species Account, Cornell Lab of Ornithology
Cory's Least Bittern
- 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