When Least Bitterns are alarmed, instead of flying away they often freeze and point their bill upward to blend with the surrounding vegetation.
The first Breeding Bird Atlas (1980-1985) reported 142 blocks and the second Breeding Bird Atlas (2000-2005) reported 129 blocks (Andrle and Carroll 1988 and McGowan and Corwin 2008). It appears that populations have declined by about 9% when comparing the two atlases. One of the most significant threats to this species is loss of appropriate habitat. New York State has lost over half of its wetlands since colonization (Tiner 1984 cited in NatureServe 2003).
The first Breeding Bird Atlas (1980-1985) reported a total of 142 blocks with 62 of those blocks as probable or confirmed breeding (Andrle and Carroll 1988). The second Breeding Bird Atlas reported Least Bitterns from a total of 129 blocks. Seventy-two of those blocks were reported as probable and confirmed breeding (Andrle and Caroll 1988 and McGowan and Corwin 2008). A comparison of the two atlases shows a 9% decline in blocks in the state (McGowan and Corwin 2008). Least Bitterns are likely overlooked during breeding bird surveys because they rarely vocalize and so, are often not heard. Least Bittern data from the Breeding Bird Survey (BBS) are too few to assess population trends in New York (Sauer et al. 2007).
Historically, Least Bitterns were considered locally common in marshes of the Great Lakes Plain, the Coastal Lowlands, and the Hudson Valley, and possibly breeding in the Champlain Valley (Eaton 1910). In the southern and western portions of the state, Least Bitterns were considered uncommon and local (Bull 1974). Generally, this species is absent from high elevations. It is difficult to determine long term trends.
New York State has lost over half of its wetlands since colonization (Tiner 1984 cited in NatureServe 2003). More recently, losses of wetlands in the Lake Plains portion of the state have been offset as agricultural lands revert back to wetlands, although net losses of wetlands in the Hudson Valley continue. Emergent marshes, which constitute only five percent of the state's 2.5 million acres, have declined overall. Equally important, the quality of remaining habitat is often degraded by fragmentation, exotic plants, and nutrient enrichment (Riexinger, personal communication, October 31, 2003). Run-off from development and agricultural practices may also negatively impact prey. Water level management of Lake Ontario may also change the quality of habitat for Least Bitterns (King 2005). Unnaturally high densities of predators may also pose a threat.
Large wetlands (>12 acres) with abundant emergent vegetation need preservation, protection, and improvement (Gibbs and Melvin 1992). Prevent chemical contamination, siltation, eutrophication, and other forms of pollution in marsh habitats. Control invasive species (such as purple loosestrife) and predators at breeding sites. When managing large wetland complexes for waterfowl, consider retaining areas with cattails and bulrush.
Population distribution, size, and trend studies are needed. Additional studies are needed on the species' breeding biology and movements. Evaluate the effects of invasive species such as common reed and purple loosestrife on breeding populations.
In New York, Least Bitterns tend to breed in shallow or deep emergent marshes, freshwater tidal marshes (lower Hudson River), or brackish tidal marshes (Long Island). They prefer stands of cattails or bulrush with bur-reed, sedges, or common reed. Stands of cattails are often interspersed with pools of open water or slow-moving channels and some woody vegetation. Large marshes are important breeding areas for this species. Open habitats such as mats of emergent vegetation are rarely used (Frederick et al. 1990 cited in NatureServe 2003).
Least Bitterns are largely restricted to the Lake Ontario and St. Lawrence River plains, and the Lower Hudson River Valley with scattered records from Long Island, Lake Champlain, the Finger Lakes, and the Mohawk Valley. They are generally absent from the Appalachian Highlands and mountainous parts of New York State (Andrle and Carroll 1988, Gibbs and Melvin 1992). On rare occasions birds have been reported mid-winter along the coast.
The breeding range of the Least Bittern extends from North America to South America. In North America, the breeding range extends from southern Manitoba and north-central United States to southeastern Canada (Ontario and Quebec), eastern Maine, and southern New Brunswick south to western and southern Texas, the Gulf coast, Florida, and Greater Antilles and west to central Montana, Utah (Great Salt Lake, formerly), eastern Colorado, and south-central New Mexico. Least Bitterns also breed in western North America in southern Oregon, interior and southern coastal California, central Baja California, and southern coastal Sonora. In Latin America, breeding Least Bitterns can be found in Guatemala, El Salvador, Honduras, Nicaragua, Costa Rica, Panama, Mexico, and elsewhere. The Least Bittern breeding range extends widely across South America including central Colombia, coastal Peru, and east of the Andes from Venezuela south to northern Argentina and southern Brazil (AOU 1983, Gibbs and Melvin 1992).
Small size, yellow color, and a dark crown are characteristics that distinguish Least Bitterns from all other bitterns and herons (Hancock and Kushlan 1984 cited in Nature Serve 2003). Diagnostic field characteristics include a vivid, greenish-black crown, back, and tail; brownish and white neck, sides, and underparts; and chestnut-colored wings with conspicuous, contrasting, pale-colored wing patches. No other small heron has large buffy patches on the upper side of the otherwise dark wings. Sexes are similar in size, but sexes are dimorphic. Females have a purple-chestnut crown and back and the neck is darkly streaked. Males have a black crown and back. Juveniles are similar to females, but the crown is more brown and paler and the breast and throat are browner and more heavily streaked. Nests are usually built over shallow water 0.3-3.3 ft (0.1-1.0 m) deep (Palmer 1962, Kushlan 1973, Aniskowicz 1981 cited in NatureServe 2003) and tend to be less than 33 ft (10 m) from open water (Weller 1961 cited in NatureServe 2003). A nesting platform with a canopy is made by pulling down and crimping surrounding emergent vegetation, such as cattail or bulrush (Weller 1961 cited in NatureServe 2003). Eggs are elliptical, pale blue or pale green, smooth and non-glossy, averaging 1.2 by 1 in (31 by 24 mm) (Bent 1926, Harrison 1978 cited in NatureServe 2003). The male's advertisement call, most frequently heard in spring, is a dove-like cooing characterized as "uh-uh-uh-uh-uh-oo-oo-oooo-oo-ooah" (Palmer 1962 cited in NatureServe 2003). Females may respond with "ticking" calls (Hancock and Kushlan 1984 cited in NatureServe 2003). When alarmed, three calls may be uttered: a loud, shrieking "quoh," a hissing "hah," or a cackling "tut-tut-tut" (Palmer 1962, Hancock and Kushlan 1984 cited in NatureServe 2003).
Least Bitterns spend nearly all their time in dense, grass-like vegetation. During the breeding season, the home range of Least Bitterns varies from 4.5-88.2 acres (1.8-35.7 hectares) with an average of 24 acres (9.7 hectares) in New York (Bogner and Baldassarre 2002).
The Least Bittern diet consists of small fishes, salamanders, tadpoles, frogs, leeches, slugs, crayfishes, dragonflies, and occasionally shrews and mice.
Least Bitterns are rarely seen in New York before late April and after September. The best time to see or hear adults is between May and July. This species is often heard and not seen. On rare occasions birds are reported during mid-winter along the coast.
The time of year you would expect to find Least Bittern active and reproducing in New York.
Ixobrychus exilis (Gmelin, 1789)
American Ornithologists' Union (AOU). 1983. Check-list of North American Birds, 6th edition. Allen Press, Inc., Lawrence, Kansas. 877 pp.
Andrle, Robert F. and Janet R. Carroll, editors. 1988. The atlas of breeding birds in New York State. Cornell University Press. 551 pp.
Aniskowicz, B. T. 1981. Behavior of a male least bittern IXOBRYCHUS EXILIS after loss of mate. Wilson Bulletin 93:395-397.
Bent, A. C. 1926. Life histories of North American marsh birds. Bull. U.S. Nat. Mus. 135.
Bogner, Heidi E. and Guy A. Baldassarre. 2002. The effectiveness of call-response surveys for detecting least bitterns. Journal of Wildlife Management. 66(4):976-984.
Brown, M., and J. J. Dinsmore. 1986. Implications of marsh size and isolation for marsh bird management. J. Wildl. Manage. 50:392-397.
Bull, John. 1974. Birds of New York State. Doubleday, Garden City, New York. 655 pp.
Cramp, S. (editor). 1977. Handbook of the Birds of Europe, the Middle East, and North Africa; the Birds of the Western Paleartic. Vol. 1: Ostrich to Ducks. Oxford University Press, Oxford, England. 722 pp.
Eaton, E.H. 1910. Birds of New York. Part 1. New York: University of State of New York. Albany, NY.
Ehrlich, P. R., D. S. Dobkin, and D. Wheye. 1992. Birds in Jeopardy: the Imperiled and Extinct Birds of the United States and Canada, Including Hawaii and Puerto Rico. Stanford University Press, Stanford, California. 259 pp.
Evers, D. C. 1992. A guide to Michigan's endangered wildlife. Univ. Michigan Press, Ann Arbor. viii + 103 pp.
Frederick, P. C., et al. 1990. Relative abundance and habitat preferences of least bitterns (IXOBRYCHUS EXILIS) in the Everglades. Florida Field Nat. 18:1-20.
Gibbs, J.P. and S.M. Melvin. 1992. Least bittern, Ixobrychus exilis. pgs. 71-88 in K.J. Schneider and D.M. Pence, eds. Migratory nongame birds of managment concern in the northeast. United States Department of the Interior, Fish and Wildlife Service, Newton Corner, MA. 400 pp.
Hancock, J., and J. Kushlan. 1984. The Herons Handbook. Croom Helm, Ltd., Kent, England. 288 pp.
Harrison, C. 1978. A Field Guide to the Nests, Eggs and Nestlings of North American Birds. Collins, Cleveland, Ohio.
Jorde, D. G., J. R. Longcore, and P. W. Brown. 1989. Tidal and nontidal wetlands of northern Atlantic states. Pages 1-26 in L. M. Smith, R. L. Pederson, and R. M. Kaminiski (editors). Habitat management for migrating and Wintering waterfowl in North America. Texas Tech. Univ. Press, Lubbock, Texas.
King, Matthew. 2005. Species group report for fresh water marsh nesting birds. Pages 97-106 of Appendix A1, Species group reports for birds in: New York State comprehensive wildlife conservation strategy. New York Department of Environmental Conservation. Albany NY.
Kushlan, J. A. 1973. Least bittern nesting colonially. Auk 90:685-686.
Kushlan, J. A. 1978. Feeding ecology of wading birds. National Audubon Society Res. Rep. 7:249-98.
Levine, E. 1998. Bull's birds of New York State. Comstock Publishing Associates, Ithaca, NY.
McGowan, K.J. and K. Corwin, eds. 2008. The Second Atlas of Breeding Birds in New York State: 2000-2005. Cornell University Press, Ithaca, NY. 688 pp.
McVaugh, W., Jr. 1975. The development of four North American herons (II). Living Bird 14:163-183.
National Geographic Society (NGS). 1983. Field guide to the birds of North America. National Geographic Society, Washington, DC.
NatureServe. 2003. NatureServe Explorer: An online encyclopedia of life [web application]. Version 1.8. NatureServe, Arlington, Virginia. Available http://www.natureserve.org/explorer. (Accessed: January 26, 2004).
New York Natural Heritage Program. 2019. New York Natural Heritage Program Databases. Albany, NY.
Palmer, R. S. (editor). 1962. Handbook of North American birds. Vol. 1. Loons through flamingos. Yale University Press, New Haven. 567 pp.
Payne, R. B., and C. J. Risley. 1976. Systematics and evolutionary relationships among the herons (Ardeidae). Univ. Michigan Mus. Zool., Misc. Publ. No. 150. 115 pp.
Sauer, J.R., J.E. Hines, and J. Fallon. 2007. The North American breeding bird survey, results and analysis 1966-2006. Version 10.13.2007. US Geological Survey, Patuxent Wildlife Research Center, Laurel, MD.
Swift, Bryan L. 1987. An analysis of avian breeding habitats in Hudson River Tidal Marshes. New York State Department of Environmental Conservation, The Hudson River Foundation for Science and Environmental Research, Inc. 62 pp.
Terres, J. K. 1980. The Audubon Society encyclopedia of North American birds. Alfred A. Knopf, New York.
Tiner, R. W., Jr. 1984. Wetlands of the United States: current status and recent trends. U.S. Fish and Wildlife Service, National Wetlands Inventory, Washington, D.C. 59 pp.
Weller, M. W. 1961. Breeding biology of the least bittern. Wilson Bulletin. 73:11-35.
Information for this guide was last updated on: July 1, 2019
Please cite this page as:
New York Natural Heritage Program. 2019. Online Conservation Guide for Ixobrychus exilis. Available from: https://guides.nynhp.org/least-bittern/. Accessed July 21, 2019.