Declining scaup populations: issues, hypotheses, and research needs

The population estimate for greater (Aythya marila) and lesser (Aythya affi nis) scaup (combined) has declined dramatically since the early 1980s to re cord lows in 1998. The 1998 estimate of 3.47 million scaup is far below the goal of 6.3 million set in the North American Waterfowl Management Plan (N AWMP), causing concern among biologists and hunters. We summarize issues of concern, hypotheses for factors contributing to the population decline, an d research and management needs recommended by participants of the Scaup Wo rkshop, held in September 1999. We believe that contaminants, lower female survival, and reduced recruitment due to changes in food resources or breed ing-ground habitats are primary factors contributing to the decline. These factors are not mutually exclusive but likely interact across seasons. Work shop participants identified seven action items. We need to further delinea te where declines in breeding populations have occurred, with a primary foc us on the western Canadian boreal forest, where declines appear to be most pronounced. Productivity in various areas and habitats throughout the breed ing range needs to be assessed by conducting retrospective analyses of exis ting data and by intensive field studies at broad and local scales. Annual and seasonal survival rates need to be determined in order to assess the ro le of harvest or natural mortality. Effects of contaminants on reproduction , female body condition, and behavior must be investigated. Use, distributi on, and role of food resources relative to body condition and reproduction need to be examined to better understand seasonal dynamics of nutrient rese rves and the role in reproductive success. Affiliations among breeding, mig ration, and wintering areas must be assessed in order to understand differe ntial exposure to harvest or contaminants, and differential reproductive su ccess and recruitment. Biologists and agencies need to gather and improve i nformation needed to manage greater and lesser scaup separately; this inclu des monitoring the breeding populations of each species separately, closer examination of existing data to improve surveys and data collection, and re -evaluation of the NAWMP population goal. These complex issues will require extensive cooperation and communication among many agencies and organizati ons in North America.