Breeds in extensive wetlands having a combination of open shallow water and dense emergent vegetation (Kaufman 1996), such as marshes, bogs, and swamps. Will also breed in brackish and salt tidal marshes and meadows (Fussell 1994, Palmer 1962).

The nest is usually built in dense vegetation, either on dry ground or in emergent vegetation just above shallow or occasionally deep water (Ehrlich et al. 1988), but it can also be on dry ground in a grassy meadow or on a floating island of a lake (Palmer 1962). Forages by wading, often at the water's edge (Kaufman 1996). Will perch on cattails and stumps, but rarely perches in trees (Palmer 1962).

NATURE SERVE GLOBAL HABITAT COMMENTS:

BREEDING: Primarily large freshwater and (less often) brackish marshes, including lake and pond edges where cattails, sedges, or bulrushes are plentiful and marshes where there are patches of open water and aquatic-bed vegetation. Occurs also in other areas with dense herbaceous cover, such as shrubby marshes, bogs, wet meadows, and, rarely, hayfields (Brewer et al. 1991). Readily uses wetlands created by impoundments. Wetlands of 2.5 ha or more may support nesting; smaller wetlands may serve as alternate foraging sites (Gibbs and Melvin 1992). See Hanowski and Niemi (1990) for a quantitative study of habitat in Minnesota.

Nests primarily in inland freshwater wetlands, sometimes in tidal marshes or in sparsely vegetated wetlands or dry grassy uplands. Breeding occurs primarily in wetlands with tall emergent vegetation. Sparsely vegetated wetlands and dry grassy uplands are sometimes used, as are tidal marshes in some areas (Stewart and Robbins 1958, Swift 1987). In comparison to the sympatric least bittern (IXOBRYCHUS EXILIS), uses a wider variety of wetland cover types, less densely vegetated sites, shallower water depths, and primarily freshwater habitats.

Wetlands used in Maine were dominated by emergent and aquatic-bed (floating-leaved and submergent) vegetation, had a high diversity of vegetative life forms, and a high degree of cover/water interspersion (Gibbs et al. in press; Gibbs and Melvin 1990). Portions of wetlands used were dominated by sedges (CAREX spp.), broad-leaved cattail (TYPHA LATIFOLIA), and ericaceous shrubs. In a study of Quebec lakes, lakes with patches of floating-leaved plants, emergent growth along shorelines, and abundant amphibian populations were preferred (DesGranges and Houde 1989).

At Horicon Marsh in Wisconsin, responded to tape-recorded calls only from shallow water cattail and dry cattail habitats and seemed to avoid deepwater cattails (Manci and Rusch 1988). At moist soil impoundments in Missouri, associated with water depths of less than 10 cm and vegetative cover characterized as 'rank, dense, or sparse.' Habitat use was not associated with 'open' or 'short' vegetative cover or water of depths of greater than 10 cm (Fredrickson and Reid 1986). In Minnesota, seven breeding territories had a mean water depth of 10 cm, vegetation height of 1.3 m, and density of sedge and grass stems of 117 stems/m squared (Hanowski and Niemi 1986).