Breeds in regularly flooded salt marshes (Fussell 1994) and brackish marshes (Harrison 1975).

May live in the wettest part of the marsh (Rising and Beadle 1996), or may place nest in a higher part of marsh not usually flooded. It is built on the ground on a dense mat of dried rushes, seaweed, or grasses, or among pieces of driftwood. It may also be placed a few inches above the ground in stems of sedge (Harrison 1975), or 7 inches to 14 feet high in a shrub or grasses (Rising and Beadle 1996). The nest is often covered by surrounding vegetation, which is woven into the nest. Nests in loose colonies (Ehrlich et al. 1988).

NATURE SERVE GLOBAL HABITAT COMMENTS:

BREEDING: A habitat specialist that occupies coastal tidal marshes throughout its range (Kale 1983, Robbins 1983). One (A. M. MIRABILIS) population in Florida commonly occurs in freshwater MUHLENBERGIA (M. FILIPES, a tussock grass) prairie (Werner and Woolfenden 1983), and another near Charleston, South Carolina, evidently avoids the outer coastal marshes for breeding and uses brackish, more sheltered marshes away from the coast (Sprunt and Chamberlain 1970). Northeastern birds occupy both high marsh (dominated by salt meadow vegetation including salt-meadow grass (SPARTINA PATENS), black-grass (JUNCUS GERARDI), glasswort (SALICORNIA spp.), and marsh elder (IVA FRUTESCENS)), and low marsh (mainly various ecological forms of smooth cordgrass (SPARTINA ALTERNIFLORA)) habitats (Woolfenden 1956, Post 1970, 1970, 1974, Reinert et al. 1981, Greenlaw 1983, Marshall and Reinert 1990). Descriptions of habitat elsewhere in the range can be found in Nicholson (1928, 1946), Tomkins (1941), Sprunt and Chamberlain (1970), Werner (1975), Sykes (1980), Post (1981), Kale (1983), Post et al. (1983), and Werner and Woolfenden (1983).

A patchy or discontinuous distribution on local marshes is exhibited throughout the range. The composition and physiognomic characteristics of occupied marsh vegetation are varied and reflect a behavioral opportunism in using available substrate (Greenlaw 1983, Post et al. 1983). Two biologically significant habitat characteristics evidently shared by most or all breeding populations are: (1) suitable elevated nest sites that offer protection from periodic tidal and storm-related flooding, and (2) nearby openings in the vegetation, or pool and ditch edges that permit access to the bases of rooted plants and open mud during foraging (Greenlaw 1992). Different microhabitats fulfill these divergent requirements for nesting and feeding. In low marshes in New York and New England, nests are commonly in areas of medium-height cordgrass (40-100 cm) growing densely enough to form a turf of partly clumped, semi-erect, persistent stems in the spring. Stands of dwarf cordgrass at or near mean high water level, and tall, open stands in the lower intertidal zone are avoided as nesting substrates. In high marshes, sparrows nest on IVA-dominated spoil deposits, or in IVA/salt meadow ecotones on the inner marsh, but they shun extensive areas of pure salt meadow grasses. Optimum habitat contains nesting and feeding microhabitats in close proximity, otherwise sparrows commute between a nest-centered territory and more distant undefended (but see DeRagon 1988) feeding areas (Tomkins 1941, Woolfenden 1956, Post 1974, Greenlaw 1983, 1992, Post et al. 1983, Marshall 1986, DeRagon 1988, Marshall and Reinert 1990).

NEST SITES: Typically elevated high enough in suitable vegetation to minimize the problem of normal flooding and low enough to be sheltered from predators and weather (Woolfenden 1956, Greenlaw 1983, Post et al. 1983, DeRagon 1988, Marshall and Reinert 1990). In New York, mid-summer nests suspended in new-growth cordgrass averaged 19.0 cm above the mud (Post 1974). Early nests are typically placed in clumps of residual cordgrass, but later nests are in the vegetation column between erect, live culms of cordgrass (Post 1974, Marshall and Reinert 1990). In the latter case, the tops of the grasses are often pulled over the nest to form a canopy (Greenlaw, pers. obs.). Occasionally, nests are placed one to four m above the ground in a shrub (usually IVA spp. in the Northeast) or small tree (Arnow 1906, Woolfenden 1956, Marshall 1986, Greenlaw 1992). In Florida, the activity of predatory rats influences nest site use by sparrows (Post 1981).