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Declining Scaup Populations:
Issues, Hypotheses, and Research Needs

Assess annual and seasonal survival rates

The role of harvest or natural mortality in the scaup population decline is uncertain. Annual survival estimates from recent analyses of banding data for lesser scaup (L. A. Reynolds, United States Geological Survey, unpublished data) and greater scaup (Rocque 1997) are similar to those reported for other duck species (Johnson et al. 1988). Survival rates for lesser scaup (1954-69) ranged from 0.44 to 0.87, with most estimates falling between 0.57 and 0.71. Survival rates for greater scaup in the Atlantic Flyway (1955-86) ranged from 0.60 to 0.83. Survival of adult females tended to be less than that of adult males for both species, and some differences were significant. However, banding data analyses for both species were constrained by low recovery rates, poor model fit, and large variances in the data. Moreover, these survival estimates only apply before the scaup population decline began in 1984; banding information is insufficient to determine survival rates during the past 20 years. More recent survival estimates for breeding lesser scaup females in the Saskatchewan parkland (1989-98; R. G. Clark, Canadian Wildlife Service; A. D. Afton, United States Geological Survey; and J. J. Rotella, Montana State University; unpublished data) and greater scaup in Alaska (1990-98; J. B. Grand, P. L. Flint, D. Esler, and T. Fondell, United States Geological Survey, unpublished data) are similar to the banding data estimates. Survival estimates are not available for scaup breeding in the WCBF, where the major decline has occurred.

Analyses of hunter-obtained wings suggest female survival rates have declined compared to males (A. D. Afton, United States Geological Survey, and M. G. Anderson, Ducks Unlimited Canada, unpublished data). The role of hunting in adult female survival is uncertain, but it may have increased in relative importance because harvest of adult scaup (including females) has remained stable in the Mississippi Flyway, where most scaup are shot, despite population declines and a lower immature:adult ratio in the harvest (G. T. Allen, D. F. Caithamer, and M. Otto, unpublished report, United States Fish and Wildlife Service 1999; A. D. Afton, United States Geological Survey, and M. G. Anderson, Ducks Unlimited Canada, unpublished data). Average harvest rate indices of scaup are low (2.9% of combined scaup population during 1961-96) and were least during 1986-93, a period when scaup populations were declining (A. D. Afton, United States Geological Survey, and M. G. Anderson, Ducks Unlimited Canada, unpublished data).

Banding and mark-resighting (including radiotelemetry) studies are critically needed to more accurately estimate annual survival and harvest rates, assess population trends, determine harvest policies, and model population dynamics. Moreover, banding and marking studies would provide important information to address philopatry; affiliation among breeding, migration, and wintering areas (see below); and the role of contaminants and harvest in the current population decline. We advocate implementing a banding program that targets breeding birds (particularly females) and bands greater and lesser scaup in all representative parts of their range to allow for differences in migration and wintering areas and population parameters. Banding in migration and wintering areas is a low priority unless there is a need to obtain annual survival estimates from such data. The relatively low densities of breeding scaup and their broad range will make logistics of such a banding program challenging; consequently, it will require commitments from federal wildlife agencies and Flyway Councils and pilot studies to assess logistics and cost-effectiveness.

Mark-resighting and radiotelemetry studies provide complementary approaches to banding programs. Such studies often provide information more quickly and on other aspects, such as natural causes of mortality. Scaup marked with satellite transmitters on the wintering grounds could provide information on frequency of multiple counting or undercounting of scaup during breeding ground surveys, as well as determine affiliations among breeding, migration, and wintering areas.

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