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Declining Scaup Populations:
Issues, Hypotheses, and Research Needs

Assess productivity in various areas and habitats throughout the breeding range

Female lesser scaup have a lower reproductive rate than most other ducks, and reproductive success is strongly age-related in prairie parkland and boreal forest habitats (Trauger 1971; Afton 1983, 1984); this likely is also true for greater scaup. Productivity may have declined due to changes in boreal forests habitats, contaminants acquired on migration or wintering areas, or nutritional condition upon initiation of egg-laying (A. D. Afton, United States Geological Survey, and M. G. Anderson, Ducks Unlimited Canada, unpublished data; Austin et al. 1999). The only long-term information available for the WCBF, collected on the Yellowknife Study Area in the Northwest Territories, indicates that pair and brood counts declined between 1962-65 and 1985-98, but brood:pair ratios have not changed (M. A. Fournier and J. E. Hines, Canadian Wildlife Service, unpublished data). Nest and hen success are extremely variable, but nest success of lesser scaup is moderate to high compared to other ducks nesting in the area (M. A. Fournier and J. E. Hines, Canadian Wildlife Service, unpublished data).

We believe that 2 approaches are needed to better understand the factors affecting scaup productivity: retrospective analyses of breeding ground survey data and new intensive field studies.

Retrospective analyses. Declining populations in the WCBF may be related to changes in habitat. Although boreal forests do not undergo dramatic droughts and floods, as occur in prairies, this biome is subject to perturbations from numerous natural and human-related factors: climate change, fire, acid rain, logging, oil and gas developments, hydroelectric developments, and mining (see Austin et al. 1999 for review). We believe the most likely contributors to habitat changes leading to widespread scaup declines in the WCBF are climate change, fire, and logging. Extensive research on effects of climate change in boreal forests is ongoing, and biologists investigating the influence of climate change on scaup should establish linkages with experts in this field. Influences of fire and logging should be addressed through retrospective analyses of breeding population data and fire or logging histories (past 20-50 years). Where possible, these investigations should be conducted at substrata or segment scales used in breeding ground surveys. Implications of climate change also should be considered in fire-related research.

New research and monitoring. We advocate 2 approaches to investigating scaup productivity that will yield information at 2 scales. One approach is to implement broad-scale monitoring of productivity indices, such as pair/brood counts and brood size, to assess spatial and temporal trends in productivity at a landscape scale. Such monitoring needs to be conducted across prairie parkland, boreal forest, and tundra areas every 5-10 years. An organization or individual should be identified to design, direct, and coordinate efforts by various state, federal, and provincial agencies. Information from this monitoring will be important for future examination of population changes at strata and substrata levels.

The second approach is to conduct intensive field studies at selected sites to obtain information on basic breeding biology of scaup and on factors affecting nesting effort, nest success, and brood survival. Intensive studies should be conducted in 4 phases: 1) delineate where declines in breeding populations have occurred (as noted above), 2) conduct pilot studies to determine feasibility (logistics, costs, etc.) of acquiring data from individually marked or unmarked scaup, 3) develop a preliminary model of population dynamics using published data and pilot studies, 4) randomly select study sites based on information from phases 1 and 2, and 5) obtain data for 4-5 years on each site. Each year, predict and then measure population change and refine and update the population model, while testing hypotheses about the underlying causes of population change. Study sites selected for comparison should include areas having declining populations and those having stable or increasing populations. Field work should be done simultaneously on several areas to allow comparisons within years.

On each study site, data should be collected on nest and hen success, nesting effort, clutch size, nutrient-reserve dynamics, and duckling survival. The preferred approach is a study of individually marked female scaup such that reproduction, survival, and philopatry can be determined concurrently. Studies of individually marked scaup would provide estimates of breeding success, survival, and molt; data from unmarked scaup include nutrient acquisition and dynamics, diet, and molt.

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