Nesting Biology of the White-Winged Scoter

Abstract

Nesting biology and productivity of white-winged scoters (Melanitta fusca deglandi) were studied on islands in Redberry Lake, Saskatchewan, and Jessie Lake, Alberta, in 1975-76. Males constituted 60% of the prenesting populations. Nest initiation peaked between 8 and 21 June, 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 hours, and mean clutch size (N = 146) was 9.17. The average incubation period for 22 clutches was 27.7 days, and 80% of all clutches hatched between 17 and 31 July. Nesting success averaged 72%. Aggregate broods formed in late July and most hens deserted their broods between 10 and 23 August. Small, mixed-age broods were common after 21 August, and total number of ducklings declined markedly thereafter. Productivity was less than 1.0 ducklings/pair on both lakes in 1976. J. WILDL. MANAGE. 45(1):38-45 White-winged scoter populations have declined in the parklands and boreal forests of northern Alberta, and in coastal and interior Alaska (Bellrose 1976:404). A dramatic decline also has occurred in southwestern Manitoba. The reasons for these declines are not known because scoters are among the least-studied waterfowl groups (Bellrose 1976:408-409), and little information is available concerning their reproductive biology. Clutch sizes have been reported for few whitewinged scoter nests (Bent 1925:132-133, Rawsl 1949:84-88, Vermeer 1969), and no information has been published on brood survival in North America. The objective of our study was to provide information on the nesting biology and productivity of white-winged scoters. Without the encouragement and assistance of F. C. Bellrose, this project would not have been initiated. We also thank L. B. Best, R. B. Dahlgren, R. D. Drobney, and L. H. Fredrickson for their reviews of the manuscript; C. E. Harris for help in the field in 1975; and R. D. Crawford, D. C. Morgan, M. R. Ryan, and D. White for their help. The Iowa Cooperative Fishery Research Unit provided a boat and motor in 1975. K. Vermeer, B. Rippen, and C. S. Houston recommended study areas.