Northern Prairie Wildlife Research Center
Declines of Greater and Lesser Scaup Populations: Issues, Hypotheses,
and Research Directions
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
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
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
- 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
- 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.
Previous Section -- What information is needed to manage
greater and lesser scaup separately?
Return to Contents
Next Section -- Literature Cited