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Canvasback Duckling Mortality: The Agassiz Story


U.S. Fish and Wildlife Service, Northern Prairie Wildlife Research Center,
La Crosse Field Station, P.O. Box 2226, La Crosse, WI 54601

Previous studies have not identified mortality factors of young-of-the-year canvasbacks nor the full extent of duckling mortality because of the potential for loss of total broods and the breakup of broods at an early age. The goal of this investigation was to develop telemetry techniques and conduct research to determine the causes and magnitude of canvasback duckling mortality. The study was conducted at Agassiz National Wildlife Refuge (NWR) in northwestern Minnesota. Thus far, data have been collected and analyzed for three spring/summer periods, 1987-89. A total of 288 ducklings have been radio-marked. Survival rates have been calculated for each sex/year class using two methods depending upon whether birds whose transmitters failed (lost birds) were assumed to be alive or dead. Survival rates were calculated based on a total of 5,692 duckling exposure days. Most mortality occurred within the first 10 days. The primary sources of mortality over the three years were exposure and mink predation. In all three years, females had lower survival than males. Total brood loss amounted to 20%, 36%, and 22% of broods released in 1987-89, respectively.
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