We monitored nest sites of endangered Interior Least Terns on a 5 095 ha alkaline flat in north-central Oklahoma, USA. After nest loss, Least Terns commonly renested and experienced 30% apparent nest success in 1995–1996 (n = 233 nests). Nest success and predation differed by location on the alkaline flat in 1995 and overall, but nest success and flooding did not differ by microhabitat type. Predation was highest at nests ≤ cm from debris (driftwood/hay) in 1995. No differences in nesting success, flooding, or predation were observed on comparing nests inside and outside electrified enclosures. Coyotes and Striped Skunks were confirmed nest predators, and Ring-billed Gulls were suspected nest predators. We identified one location on the alkaline flat of about 1 000 ha with consistently lower nest losses attributable to flooding and predation and the highest hatching success compared with other parts of the alkaline flat; it was typified by open ground and bisected by several creeks. Management activities that minimize flooding and predation in this area could further enhance nest success and theoretically increase overall productivity of this population of Least Terns. However, the efficacy of electrified enclosures and nest-site enhancements, as currently undertaken, is questionable because of considerable annual variation in use by and protection of Least Terns.