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Breeding Range. (Fig. 46). Fairly common (locally common) throughout the state, west of the Agassiz Lake Plain Region; uncommon on the Agassiz Lake Plain.

Breeding Habitat. The Marsh Hawk is a wide-ranging open-country species that frequents marshes, wet meadow of prairie ponds and lakes, lowland swales along intermittent streams, and tracts of upland prairie, particularly those that have not been heavily grazed or mowed. It is also occasional over adjoining fields of cropland or retired cropland.

Nesting. Breeding season: Late April to early August; peak, early May to mid-July. Several observations of the spectacular courtship maneuvers were recorded in central North Dakota from April 25 to May 10, during the years, 1961-1967 (RES). Extreme egg dates (110 nests): April 26 [1938] to June 25 [1939] on the J. Clark Salyer National Wildlife Refuge in McHenry and Bottineau Counties (Hammond and Henry 1949). Extreme dates of nestlings (16 nests): June 15 [1902] in Nelson County (Bishop egg collection catalog, Peabody Museum) to July 15 [1915] in Logan County (H. H. Sheldon). Nine records of dependent young on the wing were recorded between the extreme dates of July 5 [1912] in Nelson County (Bailey 1915c) and August 10 [1962] in Dickey County (RES).

Nesting sites range from deep-marsh zones of prairie ponds and lakes to upland prairie. Wetland nests were found in emergent stands of cattail, hardstem bulrush, and whitetop over water ranging up to 2 1/2 feet in depth or in clumps of shrub-willows in marginal wet meadow or swamp. Upland prairie nests were usually situated in patches of brush composed of such species as wolfberry, silverberry, and western rose. Occasionally, upland nests were located in fields of retired cropland with established growth of sweetclover, smooth brome, etc.

Indicated clutch size (39 nests): 4 to 7 eggs; mean, 5.0 eggs. Rolfe (1897a), on the basis of extensive egg collecting in the Minnewaukan area of Benson County, determined that the full clutch ranges from 3 to 5 eggs.

Figure 46. Breeding Range of Marsh Hawk.