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Declining Scaup Populations:
Issues, Hypotheses, and Research Needs

Delineate where declines in breeding populations have occurred

In Alaskan tundra areas (waterfowl breeding ground survey strata 8-11), scaup breeding populations appear stable, but populations in the boreal forest have declined since 1955 (G. T. Allen, D. F. Caithamer, and M. Otto, unpublished report, United States Fish and Wildlife Service 1999; A. D. Afton, United States Geological Survey, and M. G. Anderson, Ducks Unlimited Canada, unpublished data). Populations have declined significantly from 1978 to 1997 in central and northern Alberta, northeastern British Columbia, and the Northwest Territories; combined, this area hosts an average of 52% of the continental breeding population. Similar declines have occurred in southern Alberta, Montana, western North Dakota, and western South Dakota. More detailed analyses at the transect level indicate a broad pattern of declining scaup breeding populations for boreal forest strata east of the Continental Divide beginning about 1980 and continuing to 1997 (M. C. MacCluskie, Ducks Unlimited Canada; A. D. Afton, United States Geological Survey; and M. G. Anderson, Ducks Unlimited Canada; unpublished data). Trajectories of populations in boreal forest habitats west of the Continental Divide (interior Alaska, the Yukon Territory, and all but the northeastern corner of British Columbia) are mixed or stable.

Given these trends, we believe that research and monitoring efforts should be concentrated in the boreal forest of the Northwest Territories, northern Alberta, and northeastern British Columbia (hereafter called the Western Canadian Boreal Forest, WCBF). Further delineation of where the declines are occurring is a critical first step to addressing 2 main hypotheses about factors contributing to the decline. First, are declines in breeding populations related to habitat changes in the WCBF? This question could be addressed through retrospective analyses of population data with landscape, climate, and other habitat-related data; recommended research directions are outlined in the following section. Second, are declining populations affiliated with distinct wintering or migration areas? If populations in certain wintering or migration areas are exposed to greater contamination or sport harvest, reduced productivity or survival of that segment of the population may contribute to a long-term decline on breeding areas. Thus, we must first complete a detailed examination of existing breeding population data to determine more precisely where declines have occurred before addressing the main questions.

Another important question is whether populations of both or only 1 species are declining. Tundra strata (8-11, 13) are composed primarily of greater scaup, but their range overlaps with lesser scaup in boreal forest; only lesser scaup breed in prairie parkland. The larger component of lesser scaup in the combined population suggests that lesser scaup are a major component of the decline, but greater scaup in nontundra areas also may be declining. However, this question cannot be resolved without more information on the species composition in various breeding areas.

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