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Age and sex ratios of sea ducks wintering in the Strait of Georgia, British Columbia: Implications for monitoring


Authors

MICHAEL S. RODWAY1, HEIDI M. REGEHR1, W. SEAN BOYD2 & SAMUEL A. IVERSON3

1Wildwing Environmental Research, Box 47, Gold Bridge, British Columbia, V0K 1P0, Canada (msrodway@alumni.sfu.ca)
2Science and Technology Branch, Environment Canada, Pacific Wildlife Research Centre, RR#1, 5421 Robertson Road, Delta, British Columbia, V4K 3N2, Canada
3Department of Biology, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario, K1S 5B6, Canada 


Received 7 January 2015, accepted 9 April 2015

Date Pubished: 2015/10/15
Date Online: 2017/02/28


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Citation

RODWAY, M.S., REGEHR, H.M., BOYD, W.S. & IVERSON, S.A. 2015. Age and sex ratios of sea ducks wintering in the Strait of Georgia, British Columbia: Implications for monitoring. Marine Ornithology 43: 141-150.


Key words: age and sex segregation, age ratio, demographics, goldeneye, Harlequin Duck, immature plumage, Mergini, sea ducks, scoter, sex ratio, waterfowl


Abstract

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, the sampling intensity for each species obtained in this study provided age ratio estimates with 95% confidence limits likely within ± 5% for Surf Scoters and ± 3% for Harlequin Ducks. Regional and density-related differences in age ratios, sex ratios and adult male proportions indicated segregation and emphasize the need for broad-scale sampling to achieve representativeness. Inter-annual differences may indicate demographic changes, but few comparative data exist, and several consecutive years of surveys are needed to provide baseline data. 


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