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Northern Prairie Wildlife Research Center

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Declining Scaup Populations:
Issues, Hypotheses, and Research Needs

Determine affiliations among breeding, migration, and wintering areas

Scaup are strongly philopatric to natal and breeding areas (Johnson et al. 1988; R. G. Clark, Canadian Wildlife Service, A. D. Afton, United States Geological Survey, and J. J. Rotella, Montana State University, unpublished data) and also appear to be philopatric to migration (Afton and Hier 1991) and wintering areas (Anderson et al. 1992). Banding data indicate that scaup breeding in western Alaska migrate through the Great Lakes and winter off the North Atlantic coast (greater scaup) or else migrate through the Mississippi and Central Flyways and winter off the Gulf Coast or Florida (lesser scaup, Austin et al. 1998). However, these data are sparse and may not reflect changes in migration routes or wintering areas in the past 20-30 years (Austin et al. 1998). We also lack information on temporal and spatial patterns of spring and fall migration among tundra, boreal, and prairie parkland breeding populations. It is possible that differences in these patterns lead to differential hunting pressures and exposure to contaminants and to differential scaup reproductive success and recruitment. Therefore, a high research priority must be given to determining the movements and affiliations of greater and lesser scaup among wintering, migration, and breeding areas. As noted in earlier sections, this information is critical to our understanding of cross-seasonal influences of food resources, nutrient-reserve dynamics, contaminants, and the role of recruitment and seasonal survival in regional population changes.

Tools available to address these questions include banding, mark-resighting, and telemetry. Extensive banding studies, as recommended above, would provide valuable information on affiliations, particularly if banding were conducted on a range of breeding areas. This approach, however, involves considerable commitments of funding and manpower and long delays before sufficient data can be acquired for analyses. Satellite telemetry studies, although expensive, would yield more immediate information from which other studies could be designed.

Alternatively, the question of philopatry and affiliation to breeding areas may be evaluated by applying stable isotope techniques to feathers of hunter-shot or trapped scaup. This approach can provide answers about general breeding origin (primarily latitude) of hatching year and possibly adult female scaup to specific migration and wintering sites from year to year; general molting areas (latitude) of adult male scaup; and annual breeding site affinity of scaup shot throughout the hunting season in different migration and wintering areas. The main advantage of this approach is that answers may be obtained relatively quickly for certain cohorts (e.g., breeding origin of hatch-year scaup, molting location of adult males), but weaknesses include cost (initial refinement of the existing isotope model and development of cheaper analytical methods) and only general information about breeding origins, albeit perhaps sufficiently precise to test the main question posed above.

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