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Declining Scaup Populations:
Issues, Hypotheses, and Research Needs

Gather and improve information needed to manage greater and lesser scaup separately


Although greater and lesser scaup often are considered to be similar ecologically, the 2 species differ in breeding ecology, feeding ecology, distribution, and other aspects (Bellrose 1980). Because lesser scaup are more numerous in North America, they tend to dominate our management and interpretation of combined population and survey data. To appropriately manage and conserve these species, we must understand their differences and acquire information on population trends, survival, and harvest for each species. To obtain the necessary information, we need to: 1) separate the 2 species in surveys; 2) examine existing data to improve survey designs and data collection; and 3) obtain current survival, recovery, and harvest estimates (discussed above). We also should reevaluate the population goal of the NAWMP in light of recent information and consider separate goals for each species.

Separate the 2 species in surveys. We have a general concept of the breeding and wintering distribution of greater and lesser scaup, but there is no systematic information on the proportion of each species in breeding or wintering ground surveys. Therefore, it is critical that a practical way to separate the 2 species in breeding ground surveys be developed. Having this ability is critical to the long-term monitoring of each species' population and also to studies examining potential factors contributing to the continental population decline, such as exposure to hunting, contaminants, and food resources. Separation of the species (which is dependent on viewing the extent of white on the wing) cannot be done effectively from aircraft because scaup tend not to flush for fixed-wing aircraft and they dive or hide when low-flying helicopters approach (J. Goldsberry, United States Fish and Wildlife Service, personal communication). Consequently, we advocate conducting a ground survey across a portion of the surveyed area to determine the proportion of greater versus lesser scaup in selected areas. Before the survey is implemented, a preliminary database should be developed using existing information, such as area wildlife surveys, impact statements, summer breeding bird surveys, and other unpublished data sources, and a pilot ground study should be conducted to refine techniques and logistics on sample areas thought to contain mostly greater scaup and a few areas containing a mix of the 2 species. Sampling design should account for patchy distribution of the 2 species among habitats. Expense and logistical challenges of such a survey will be great, but without it we cannot effectively manage the 2 species separately, and cannot appropriately understand the contribution of greater versus lesser scaup to continental population trends. Moreover, such a survey also could provide better distribution data for other waterfowl species.

Separation of species also is needed for migration and wintering surveys. This task also will require ground surveys, which may have to be repeated over several years to account for any weather-related influences on distribution. Surveys in these areas will have special challenges, such as inclement weather and the distribution of many scaup in offshore areas. Some information could be obtained from review of existing published and unpublished data, such as Christmas bird counts and wildlife area surveys. Information on species distribution in migration and wintering areas, in combination with species-specific harvest data, would allow harvest management where the species are geographically separated during a portion of the hunting season.

Examine existing data to improve surveys and data collection. We believe that much more can be learned from existing data. Additional analysis of breeding ground survey data can lead to improvements in survey design. This survey, which is timed for mallards (Anas platyrhynchos), has several known and suspected biases relative to breeding scaup because of their later migration (W. F. Crissey, United States Fish and Wildlife Service, unpublished report, 1975; Austin et al. 1998; A. D. Afton, United States Geological Survey, and M. G. Anderson, Ducks Unlimited Canada, unpublished data). More detailed analysis should examine social groupings, distribution, and timing of the survey, and consider the possibility of restratification of the survey for scaup. A June survey, which could provide a more accurate scaup population estimate, should be evaluated. In addition, analyses should compare breeding population trends of species with a similar breeding range (e.g., American wigeon [Anas americana], bufflehead [Bucephala albeola], and common goldeneye [B. clangula]) relative to those of scaup.

Review of migration and wintering data is needed, including individual state migration surveys, Great Lakes surveys (e.g., Long Point, Ontario), midwinter data, and other count data that may be available. These reviews could provide information on recent and historical changes in scaup distributions and biases of and potential improvements for survey design. New or expanded surveys could be further justified based on other species that are either surveyed poorly or thought to have declining populations, such as scoters (Melanitta spp.), oldsquaw (Clangula hyemalis), and mergansers (Merganser spp.). Surveys should be coordinated with Seaduck Joint Venture efforts.

We believe that a thorough review of the Parts Collection Survey data and possibly state or refuge bag-check data would provide information on distribution, age, and sex for each species. Additional bag checks or special wing surveys in selected areas may provide information on species composition, age, and sex.

Reevaluate the NAWMP Population Goal. In 1986, NAWMP established a goal of 6.3 million scaup (both species combined) by the year 2000 (United States Fish and Wildlife Service and Canadian Wildlife Service 1986); this was based on the estimated average number of scaup present during 1970-79 (6,305,195). Breeding scaup numbers have not met this goal since 1984. Rather than reconsider the appropriateness of the current NAWMP population goal for the combined scaup population, we should move toward new and separate goals for each species. We recommend that the NAWMP population goal be a separate, measurable goal for each species and that the goal population size be determined by 2005.


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