Appearance. The least bittern is the smaller of Minnesota's two bittern species. This slender member of the heron family is about 12 inches long with a wingspan of about 17 inches. Its dark, nearly black cap and back contrast with bright yellowish-brown plumage on the face, sides of neck, and wings. Its whitish throat and underparts have long, broad, brown streaks. The bill and legs are yellowish-green. The American bittern is much larger and heavily streaked. The green heron, sometimes mistaken for a least bittern, has a greenish back and purplish-brown neck.
Habitat. In Minnesota this species is found almost exclusively in marshes, primarily those dominated by cattails. Least bitterns prefer a good interspersion of cattails and open water, where they forage at the water's edge. Least bitterns are less likely to occur in narrow cattail borders around lakes or in very dense cattails without any open water nearby.
Range. Uncommon breeding residents in marshes scattered throughout much of Minnesota, they are rare in northeastern Minnesota and elsewhere in the state where their preferred habitat is lacking. Least bitterns spend winter in the southern United States and Central America. Least bitterns can be found in suitable habitat throughout the eastern United States and southeastern Canada, patchily in western states, and southward through much of Central and South America.
Behavior. This very slender bird can straddle plant stalks and move with ease through thick marsh vegetation. It can be relatively secretive and therefore overlooked. Most often seen when flushed, it flies weakly just above the cattails before dropping out of sight. It can sometimes be spotted foraging at the edge of open water. When alarmed, it holds its beak erect, mimicking marsh vegetation. The least bittern may build a small platform of vegetation from which it forages for aquatic insects and small fish. It constructs a covered nest of marsh plants elevated above water.
Song. The call of the least bittern is the best indication of its presence in dense, marshy vegetation. Most commonly heard is a distinctive series of coo-coo-coo notes, all on one pitch. The black-billed cuckoo makes somewhat similar calls but without the unique hollow-sounding quality of the least bittern's notes.
Status. North American Breeding Bird Surveys have shown an annual decline of around 4 percent for least bitterns in Minnesota. The State Wildlife Action Plan identifies the bird as a species of greatest conservation need due to its population decline and restricted wetland habitat. Any further destruction of wetlands would negatively affect this species. In some wetlands, invasive aquatic plants such as hybrid cattail and purple loosestrife are making vegetation too dense for least bitterns.
Steve Stucker, DNR Ecological and Water Resources