The Least Bittern (Ixobrachus exilis) is the Western Hemisphere's smallest heron. Roughly the size of a robin, this chestnut, black, and buff-colored bird is extremely secretive in its habits.
Listed as Threatened in New York, the species summers in three principal areas of the state. The most important breeding grounds in one of these regions is the North Bay and Stockport Flats complex, along with the Tivoli marsh.
Least Bitterns prefer marshes larger than 12 acres, where they generally nest alone. In very large marshes they're known to concentrate in loose colonies, as they do in Hudson and Greenport.
In our region, the bird's preferred freshwater tidal marshes are themselves rare. Throughout the state, "the majority of occurrences [of these marshes] are on the Hudson River, with over 75% in Greene, Columbia, and Dutchess Counties" (New York Natural Heritage Program).
In the 1980s when the NYS Department of State began in earnest to protect the state's coastal resources - including traditional uses such as hunting, fishing and recreation - the North Bay was designated a Significant Coastal Fish and Wildlife Habitat.
In 2004, as a means to draw attention to the bay's vulnerable water birds, but especially North Bay's breeding population of Least Bitterns, the National Audubon Society included the Hudson North Bay (first bay) in its "Important Bird Area Program."
Much remains unknown about this rarely encountered heron. With their long toes, bitterns make superb climbers through emergent vegetation, foraging in deeper waters than most other wading birds.
When approached, they tend to slip away unseen. To show how easily they pass between the crowded stems of cattails, flags, and arum, John James Audubon conducted the following experiment with a live bittern. "This bird was able to contract its body so as to pass between two books set an inch apart without moving them [yet] when the bird was dead its body measured two and a quarter inches in diameter" (Forbush, 1925).
Least Bitterns are feeble fliers at ground level and are almost never seen in migration. In May 2013, a single migrating individual flew at a height of 200 feet above the Hudson River while dropping into the city's South Bay. (This remains the only bittern record for the smaller and busier South Bay.)
In New York, the birds rarely arrive before May from their wintering grounds in the southern United States, the Caribbean, Mexico, and Central America. After the young are fledged, they rarely linger beyond September. Least Bitterns have never been recorded in winter in upstate New York.
On November 19, 2012, a single Least Bittern was observed in Hudson's first bay surpassing the state record previously held this far north since recording began in the 19th century (see "Kingbird"; New York State Ornithological Union, Vol. 63 No. 1, March 2013, p. 66).
Highly sensitive to human disturbance, Least Bitterns can still be found near urban environments, such as the Hudson North Bay. As quietly, they will disappear from areas subject to new development.
Among its known pressures are habitat loss, predation, exotic flora, and water pollution.
The DEC's New York Natural Heritage Program recommends the prevention of chemical contamination, siltation, eutrophication, and other forms of pollution in marsh habitats as a Least Bittern conservation strategy for the state. It cites "run-off from development" as a pressure on the bird's food source.
Population studies which require specialized surveying techniques are still being developed (in the mid-Hudson area the Canada Protocol is used for surveying). Although population and demographics are too poorly understood for purposes of federal regulation, Least Bitterns are provided special protections on a state-by-state basis.
The Least Bittern is Endangered in Maine, Massachusetts, and Pennsylvania. It is Threatened in New York, Connecticut, Rhode Island, Ohio, and Michigan, and Threatened in Canada from Manitoba to New Brunswick. (“Threatened” means that although a species is not endangered, it's likely to become endangered in the foreseeable future if steps are not taken to address the factors which threaten it.) Least Bittern is a species of Special Concern in Vermont, New Jersey and New Hampshire.
Any habitat in New York which supports Least Bitterns is a state-wide asset deserving of special attention. It should be recognized, however, that any added scrutiny favoring the conservation of these birds and their habitats is not necessarily automatic.
For this reason, Least Bittern habitat protection often depends on local knowledge and local interest.
Male Least Bittern in First Bay
Male Least Bittern in Hudson's North Bay (First Bay)
