Nest is built on the ground, often in a depression, at the base of a plant and concealed by overhanging vegetation; some are up to 19.5 inches above the ground, attached to a vertical stem (Rising and Beadle 1996). Nests semi- colonially (Potter et al. 1980).

NATURE SERVE GLOBAL HABITAT COMMENTS:

BREEDING: Open fields and meadows with grass interspersed with weeds or shrubby vegetation, especially in damp or low-lying areas, adjacent to salt marsh in some areas. Uses unmowed hayfields (abandoned if cut). Found in a variety of habitats that contain tall, dense grass and herbaceous vegetation (Smith 1968, 1992). Hyde (1939) describes a variety of preferred habitats: upland weedy hayfields or pastures without shrubs, wet meadows, drier areas of saltmarshes, grassy fields, and sedgy hillsides with recently planted pine seedlings (PINUS spp.). Graber (1968) found that their habitat was usually quite dense from 30-61 cm off the ground and reported them to be 'adapted' to unmowed hayfields. In New York, Peterson (1983) found them in large, ungrazed fields, often on hilltops, with a variety of moisture regimes and no woody invasion. They are not typically associated with grazed areas (Peterson 1983, Zimmerman 1988), although they can survive quite well in pastures that are only lightly (Skinner 1975) or moderately (Smith and Smith 1992) grazed. Wiens (1969), in his three year study, found four territories in the first and third years and none in the second year. He found that territories had a low percent cover of forbs, dense vegetation, a high effective vegetation height, little bare ground or low vegetation, and no trees, posts, or fence lines.

In eastern part of range, are reported in '...moist upland meadows not under the plow, grown up to clumps of ferns, tall meadow rue (THALICTRUM spp.), and scattered shrubbery' in Vermont (Kibbe and Laughlin 1985); '...in small swales, meadows or other moist grassy lands...in fields of heavy timothy or clover' in Massachusetts (Forbush 1929); and '...in grassy fields and meadows with scattered bushes and herbaceous plants, both in wet and dry situations' in New York (Bull 1974). In addition to the above types of habitats, occurrences have been reported in wet meadows vegetated by sedges (CAREX spp.), rushes (SCIRPUS spp.) and grasses, in fields of seedling pines, and in drier upland portions of saltmarshes in the Northeast (Craig 1979).

Along the Atlantic Coast, the birds probably nested on the edges of saltmarshes before the arrival of Europeans (Hyde 1939, Craig 1979). In West Virginia, Hall (1983) reports that Henslow's sparrows '...prefer fields with growths of orchard grass [DACTYLIS GLOMERATA] or a rank weedy growth.' Birds in Maryland have occurred chiefly in broomsedge (CAREX SCOPARIA) fields and weedy sedge meadows, and occasionally in hayfields (Stewart and Robbins 1958). Near Louisville, Kentucky, '...exclusively in or near fields largely or wholly composed of the orchard grass much raised locally as a crop, and has preferred the crop fields to patches of untended grass' (Mengel 1965). In Kentucky, Mengel (1965) noted that the sparrow often occurred in association with sedge wrens (CISTOTHORUS PLATENSIS) and in dry, upland sites that were in marked contrast to the marshy, meadow habitats considered typical habitat by Hyde (1939).

In the Midwest and Great Plains regions, formerly bred in tallgrass prairie interspersed with forbs and shrubs. Where tallgrass prairie persists, J. Zimmerman (pers. comm.) reports that they still use it for nesting habitat in Kansas and Missouri. Presently, typical breeding habitat includes neglected grassy fields, pastures and meadows with scattered shrubby vegetation, or hayfields with dense cover, usually in damp or low-lying areas (Whitney et al. 1978, Johnsgard 1979, AOU 1983).

In a brome grass/alfalfa/red clover hayfield in southwestern Michigan, they bred in areas with an intermediate moisture range, a continuous cover of grasses and sedges about 0.8 m high, occasional shrubs, mostly less than 0.9 m high, and accumulated litter (no data on litter depth or percent coverage) (Robins 1971).

Fall and Eliason (1982) located a nest in Hennepin County, Minnesota, at the top of a knoll in an old field. Timothy comprised about 80% of the biomass of the 0.5 m-high vegetation. Except for a few shrubs approximately 0.5 m-high, there was no woody vegetation within 100 m, the vegetation covered about 75% of the soil surface, and there was a complete litter layer up to five cm deep.

Wiens (1969) compared the vegetation structure at nests with the vegetation in unoccupied areas in Fitchburg, Wisconsin. Occupied areas had significantly lower coverage and density of forbs, especially broad-leaved types, and the forb height was significantly greater (occupied average height = 27 cm). In occupied areas, the vertical vegetation density was higher and the litter was deeper and covered a higher percentage of the soil surface (average depth = 4.3 cm, 93% coverage).

Nest is well-hidden in grass, either at base of grass tuft (usually) or to 40 cm up in stems of growing herbage.