Rodway et al.: Age and sex ratios of sea ducks wintering in the Strait of Georgia 141 Marine Ornithology 43: 141–150 (2015) AGE AND SEX RATIOS OF SEA DUCKS WINTERING IN THE STRAIT OF GEORGIA, BRITISH COLUMBIA: IMPLICATIONS FOR MONITORING

In research on sea ducks, winter age and sex ratios provide valuable demographic data that are difficult to obtain by other means. Our objectives were to determine spatial, temporal, and density-related variability in (1) age and sex ratios for five sea duck species and (2) proportions of adult males for eight species that winter in the Strait of Georgia, British Columbia, Canada. Kilometre-long shoreline sections (n = 49–62) were surveyed in early February in three years: 2003, 2004, and 2014. Annual estimates for male age ratio (first year:adult male) varied significantly for Black Scoter Melanitta americana (0.071 to 0.170), Surf Scoter M. perspicillata (0.064 to 0.101) and Harlequin Duck Histrionicus histrionicus (0.068 to 0.138). Regional differences in male age ratio were found for Barrow’s Goldeneye Bucephala islandica (0.034 to 0.197) and Common Goldeneye B. clangula (0.033 to 0.165), and more complex interactions were found between regions by year for Surf Scoter. Sex ratios were less variable than age ratios and varied consistently by year and region only for Common Goldeneye. Adult male proportions were correlated with but varied more than sex ratios and showed significant differences by year for Surf Scoter, Common Goldeneye and Bufflehead B. albeola and by region for Surf Scoter, Common Goldeneye, Bufflehead and Red-breasted Merganser Mergus serrator. Based on previous research that calculated expected confidence limits from different numbers of occupied survey sections, th