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)
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Information for this guide was last updated on: July 1, 2019
Please cite this page as:
New York Natural Heritage Program. 2020. Online Conservation Guide for Ixobrychus exilis. Available from: https://guides.nynhp.org/least-bittern/. Accessed July 2, 2020.