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Breeding Range. (Fig. 75). Generally uncommon and local throughout the Prairie Pothole Region and on the Coteau Slope; rare and local in the Agassiz Lake Plain Region (recorded in Pembina, Walsh, Grand Forks, and Cass Counties).

Ordinarily, the local breeding populations of this semi-colonial species are represented by small groups that are composed of fewer than 20 pairs. Appreciably greater numbers do occur, however, on Lake Alice in Ramsey County and on the J. Clark Salyer National Wildlife Refuge in McHenry and Bottineau Counties.

Breeding Habitat. Characteristic of large marshes that occur in natural lake basins or on shallow river impoundments that are managed for waterfowl. The nesting habitat requirements of the Forster's Tern and Franklin's Gull appear to be quite similar since breeding populations of the two species are often associated together in the same marsh.

Nesting. Probable breeding season: Late May to late July. At the J. Clark Salyer National Wildlife Refuge, nests contained one to three eggs on June 16, 1949 and chiefly two eggs on July 2, 1950 (refuge record file). On July 8, 1971, a nest with two eggs was found in Emmons County (RES). Newly hatched young were recorded on the J. Clark Salyer National Wildlife Refuge on June 21, 1964 (A. M. Gammell) and on July 2, 1950 (refuge record file).

The nests are similar to those of the Black Tern in that they are situated on floating vegetative debris composed of algae, submerged vascular plants, or prostrate leaves and stems of emergent marsh plants.

Figure 75. Breeding Range of Forster's Tern.