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Declining Scaup Populations:
Issues, Hypotheses, and Research Needs

Introduction


The combined breeding population of greater (Aythya marila) and lesser scaup (A. affinis) is larger than that of any other diving duck and most dabbling duck species in North America (United States Fish and Wildlife Service 1998). Scaup also have the most widespread distribution of all North American diving ducks, extending in North America from the northern tundra in summer to southern Mexico in winter (Austin et al. 1998). Greater and lesser scaup are not counted separately because they are difficult to distinguish during surveys. Lesser scaup are estimated to constitute 89% of the continental scaup population (Bellrose 1980, Austin et al. 1998). During the 1970s and early 1980s, the combined scaup population ranged from 5 to >7 million (Figure 1). During 1978-97, the combined scaup population declined steadily by 150,491 per year (A. D. Afton, United States Geological Survey, and M. G. Anderson, Ducks Unlimited Canada, unpublished data). By 1998, the breeding scaup population was 3.47 million, a 16% decline from 1997 and the least recorded since breeding waterfowl surveys began in 1955 (United States Fish and Wildlife Service 1998). This population estimate is far below the goal of 6.3 million set in the North American Waterfowl Management Plan (NAWMP, United States Fish and Wildlife Service and Canadian Wildlife Service 1986, United States Fish and Wildlife Service 1998), causing serious concern among biologists and hunters.

Figure 1: Numbers of scaup
Figure 1. Annual estimates and 95% confidence intervals of numbers of breeding scaup (greater and lesser scaup combined) in the traditional surveyed area of the Waterfowl Breeding Ground Population and Habitat Survey (United States Fish and Wildlife Service unpublished data) and annual numbers of scaup (greater and lesser scaup combined) counted during the Midwinter Waterfowl Survey (United States Fish and Wildlife Service, unpublished data). Modified from Afton and Anderson (unpublished data).

Two recent reviews (G. T. Allen, D. F. Caithamer, and M. Otto, United States Fish and Wildlife Service 1999, unpublished report; A. D. Afton, United States Geological Survey, and M. G. Anderson, Ducks Unlimited Canada, unpublished data) provide important baseline information and assessments of the current status of scaup populations. These studies indicate: 1) the combined scaup population has declined significantly over the past 20 years, with widespread and consistent declines within surveyed areas of the western Canadian boreal forest; 2) proportions of female lesser scaup in the harvest have declined; and 3) proportions of young lesser scaup have declined, especially in the Mississippi Flyway. Afton and Anderson (unpublished data) interpreted these findings as strong evidence that scaup reproductive success has declined over the past 20 years, particularly in the western Canadian boreal forest, and that female survival rates have declined compared to males.

The United States Geological Survey's Northern Prairie Wildlife Research Center hosted a workshop on 9-10 September 1998 for biologists to share information on scaup and discuss research needs and opportunities for collaboration. The workshop was sponsored by the United States Geological Survey (USGS) and Ducks Unlimited Canada. Dr. James K. Ringelman, Ducks Unlimited, Inc., was facilitator. Forty-five biologists participated, including representatives from USGS research centers and cooperative research units; United States Fish and Wildlife Service's Office of Migratory Bird Management, Office of Research Coordination and Alaskan refuges; Environment Canada; Ducks Unlimited Canada's Institute for Wetland and Waterfowl Research; universities; Long Point Waterfowl and Wetlands Research Fund; and state representatives of the Atlantic, Mississippi, and Central Flyways. A detailed summary of the workshop, including information presented in oral papers and abstracts during the workshop, is provided by Austin et al. (1999).

This paper summarizes issues of concern, hypotheses for factors contributing to the population decline, and research and management needs recommended by workshop participants. Participants summarized issues into 4 main questions, similar to the ideas outlined in Afton and Anderson (unpublished data): 1) have changes in western Canadian boreal forest resulted in reduced reproductive success of scaup; 2) have physiological changes (nutrient acquisition, contaminants) affected reproductive success of scaup; 3) has reproduction or survival of scaup changed sufficiently to cause population declines and, if so, what was the cause; and 4) what information is needed to manage greater and lesser scaup as separate species? Numerous action items were embraced by the group:

1) Delineate where declines in breeding populations have occurred.
2) Assess productivity in various areas and habitats throughout the breeding range.
3) Assess annual and seasonal survival rates.
4) Investigate effects of contaminants on reproduction, female body condition, and behavior.
5) Examine use, distribution, and role of food resources relative to body condition and reproduction.
6) Determine affiliations among breeding, migration, and wintering areas.
7) Gather and improve information needed to manage greater and lesser scaup separately.

In each section below, we provide background information, highlight key ideas discussed, and provide recommendations to address research and information needs.


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