Cuthbert, F.J., and M.C. Louis. 1986. The Forster's tern in Minnesota: status, distribution, and reproductive success. Final report to Minnesota Department of Natural Resources. 22 pp.
Forster's Terns (Sterna foresteri) were studied in Minnesota from 1985-1986 to determine abundance, breeding distribution, and reproductive success. In both years, the estimated breeding population was 900-1000 pairs. The Forster's Tern breeds throughout the western prairie wetlands and eastward through the prairie-woods transition including an extension into the central part of the state to the Twin Cities. The largest colonies were in Jackson, Nicollet, Todd, and Wright counties. Although the major colonies were found at sites traditionally used by Forster's Terns for most of this century. site occupancy in any given year was determined by water level and presence of suitable nest habitat. Reproductive success varied among colonies, ranging from 0.00 to 0.458 fledglings/breeding pair. High water levels, wind and wave damage and predation by Great Horned Owls (Budo virginianus) were the primary factors that reduced reproductive success. Reproductive success recorded during this study was below that needed to maintain the population at its current size. To ensure conservation and appropriate management of this species in Minnesota, major colonies need to be monitored annually to estimate colony size and productivity.