Nesting biology and productivity of white-winged scoters (M. fusca deglandi) were studied on islands in Redberry Lake, Saskatchewan, and Jessie Lake, Alberta [Canada], in 1975-1976. Males constituted 60% of the prenesting populations. Nest initiation peaked between June 8 and 21, and most nests were under dense shrubs at least 50 m from the nearest shoreline. The mean laying rate for 8 females was 1 egg every 34.4 h, and mean clutch size (146) was 9.17. The average incubation period for 22 clutches was 27.7 days, and 80% of all clutches hatched between July 17 and 31. Nesting success averaged 72%. Aggregate broods formed in late July and most hens deserted their broods between Aug. 10 and 23. Small, mixed-age broods were common after Aug. 21, and total number of ducklings declined markedly thereafter. Productivity was less than 1.0 ducklings per pair on both lakes in 1976.