Declines of Greater and Lesser Scaup Populations: Issues, Hypotheses, and Research Directions
Conclusions
The consensus of workshop participants was that scaup populations have declined. BGS numbers are down and age ratio in harvest for lesser scaup has declined, indicative of poor recruitment. Analyses of BGS data by MacCluskie et al. indicate that the scaup decline occurred primarily in Canada's western boreal forest, east of the continental divide. This is the primary breeding range for lesser scaup. Whether greater scaup breeding there also are declining is unknown.
Various factors may be contributing to these declines, and extensive research and analyses are needed to identify them. Contaminants, lower female survival, and reduced recruitment due to changes in breeding-ground habitat or food resources are believed to be the primary factors contributing to the scaup decline. These factors are not mutually exclusive and likely interact across seasons. The range of issues and of geography involved makes addressing these hypotheses complex.
Several themes were repeated in discussions and recommendations. These highlight research and information needed to address the hypotheses examined here and in Afton and Anderson (in review).
- Continue detailed examination of existing data.--Much information remains in the BGS, harvest, and other data sets. These need to be examined for biases, errors, and patterns, including possible changes over the past 20-30 years. Such evaluations could lead to improved surveys and assessments of population trends. Retrospective analyses of these data sets with other information, such as habitat or climate changes, could provide insight into these issues.
- Determine affiliations of scaup among breeding, migration, and wintering grounds.--This information is critical to understanding cross-seasonal influences of food resources, nutrient-reserve dynamics, contaminants, and the role of recruitment and seasonal survival in regional population changes. Although banding data provided some insight into the flyway distributions of scaup, these distributions patterns likely have shifted in the past 20 years due to changing food resources on migration and wintering areas. Therefore, a key research priority must be to determine movements and associations of greater and lesser scaup among wintering, migration, and breeding areas. Extensive summer banding on breeding grounds and telemetry (including satellite telemetry) would provide this information but these will be difficult and likely expensive.
- Develop separate population estimates for greater and lesser scaup in surveys.--Although most evidence suggest that lesser scaup are declining, we cannot discern whether greater scaup breeding in the western Canadian boreal forest also are declining. Clarification of each species' distribution in surveyed areas will be important for long-term monitoring and conservation of each species, and also for understanding factors contributing to the continental decline. Although we often consider greater and lesser scaup as very similar ecologically, they differ in breeding ecology, feeding ecology, distribution, and other aspects. Separation of the 2 scaup species in migration and midwinter surveys is needed to better delineate their distribution and exposure to hunting and contaminants and to examine food resources issues.
- Improve estimates of survival.--Clearly needed are extensive banding and mark/resighting studies to address breeding success, philopatry, and seasonal and annual survival rates. These studies are most needed on breeding areas to examine factors contributing to differential population dynamics among areas. Banding and marking can help us examine the role of contaminants and harvest in the population decline. Improved survival estimates are critical for determining harvest policies, assessing population trends, and modeling population dynamics.
- Examine reproductive success across a range of areas.--Most research was conducted before the start of the population decline. New studies, particularly in the Boreal Forest biome, are needed to examine reproductive success in areas where populations are declining and compared to sites where populations are stable or increasing. Such studies will allow assessment of the role of reproduction in the current decline, and of the factors contributing to any decline in productivity.
Two actions would help guide future efforts and reduce redundancy: (1) a website or periodic newsletter, to keep participants and others interested in scaup informed about current research plans, activities, and opportunities for collaboration, and (2) a designated coordinator for some studies, particularly examination of existing survey and harvest data and banding studies. Work by Allen et al. (1999) and Afton and Anderson (in review) provide a baseline for additional analyses.
Several participants suggested that a conservation plan, as done for seaducks, and an on-going working group would be valuable to provide information on scaup issues to concerned individuals and groups. A workshop focusing on scaup should be conducted at the Second International Duck Symposium at Saskatoon, Saskatchewan, in the fall of 2000.
Effective conservation of North American waterfowl requires cooperation and communication among agencies and organizations in the U.S., Canada, and Mexico. This workshop is the first step in focusing research directions and stimulating communication and partnerships among diverse groups concerned with scaup conservation and management. All of the recommendations presented here will require funding, commitments of personnel time and other resources, and partnerships and cooperative studies. We encourage all involved with scaup to keep others informed of their activities, and to seek opportunities for collaboration and interactions. We challenge the U.S Fish and Wildlife Service, U.S. Geological Survey, Canadian Wildlife Service, Flyway Councils and Technical Committees, and private conservation organizations to commit personnel and funding necessary to begin answering research and information needs identified at this Workshop. These steps should begin immediately to address possible causes of scaup population declines. With scaup showing a long-term decline of ~150,000 birds per year, the need for immediate action is clear.
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