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Declines of Greater and Lesser Scaup Populations: Issues, Hypotheses, and Research Directions

Introduction


The combined breeding population of greater (Aythya marila) and lesser scaup (A. affinis) is larger than that of any other diving duck species and greater than that of most dabbling ducks in North America (U.S. Fish and Wildlife Service 1998). Scaup are the most widespread of North American diving ducks (Tribe Aythini), extending from northern tundra in Alaska and Canada 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 aerial surveys, so distinguishing specific trends is not possible. 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). Scaup and most other North American waterfowl species experienced population declines during the prairie drought in the late 1980s and early1990s. From 1986 to 1993, most principal duck species, including scaup, were below goals of the North American Waterfowl Management Plan (NAWMP; U.S. Fish and Wildlife Service 1986, 1998).

GIF-Figure 1. Annual estimates and 95% confidence intervals of greater and lesser scaup (combined) in the traditional surveyed area of the Waterfowl Breeding Ground Population and Habitat Survey(U.S. Fish and Wildlife Service unpubl. data), and Midwinter Waterfowl Servey(U.S. Fish and Wildlife Service unpubl. data).  Modified from Afton and Anderson (in review).

Figure 1. Annual estimates and 95% confidence intervals of greater and lesser scaup (combined) in the traditional surveyed area of the Waterfowl Breeding Ground Population and Habitat Survey(U.S. Fish and Wildlife Service unpubl. data), and Midwinter Waterfowl Servey(U.S. Fish and Wildlife Service unpubl. data). Modified from Afton and Anderson (in review).

Water conditions in the prairie pothole region improved markedly in 1994 and generally have remained good through 1998 (U.S. Fish and Wildlife Service 1998). Populations of all principal duck species except scaup have increased since 1993. By spring 1997, only scaup and northern pintail (Anas acuta) populations remained below NAWMP goals and their respective long-term averages. Although the pintail population has increased, the scaup population has continued a nearly steady decline since the mid-1980s. In spring 1998, the breeding scaup population was 3.47 million, a 16% decline from 1997, and the lowest recorded since surveys began in 1955 (U.S. Fish and Wildlife Service 1998).

On average, 7% of scaup were counted in Tundra, 25% in Prairie-Parklands, and 68% in Boreal Forest biomes during 1955-97 (Afton and Anderson, in review) (Figures 2 and 3). Thus, drought or habitat degradation in the Prairie Pothole Region should have less direct effect on the continental breeding scaup population than on other diving ducks such as canvasback (Aythya valisineria) or redheads (A. americana), which predominantly occur in the Prairie Pothole Region. Many studies have evaluated relationships of waterfowl populations with conditions in the Prairie Pothole Region, but no study has examined similar relationships in the boreal forest. Low densities of breeding scaup (relative to the Prairie Pothole Region) and difficult field logistics have limited studies conducted in the Boreal Forest biome.

Concerns about the declining combined population have led to increasing interest and research efforts on greater and lesser scaup. Afton and Anderson (in review) and the U.S. Fish and Wildlife Service (FWS) (Allen et. al. 1999) have evaluated scaup population data based on breeding and wintering ground surveys and band return data. Rocque and Barclay (1999) have examined greater scaup survival rates and populations in the Atlantic Flyway. The Institute of Wetland and Waterfowl Research of Ducks Unlimited, in cooperation with the Louisiana Cooperative Fish and Wildlife Research Unit, is developing a research initiative on scaup. Other biologists plan to publish previously collected data or are considering new research.

GIF-Figure 2. Annual estimates of breeding greater and lesser scaup (combined) in the Tundra (strata 8-11), Boreal Forest (strata 1-7, 12-25, 50, and 77), and Prairie-Parkland biomes (strata 26-49, and 75-76).  From Afton and Anderson (in review).

Figure 2. Annual estimates of breeding greater and lesser scaup (combined) in the Tundra (strata 8-11), Boreal Forest (strata 1-7, 12-25, 50, and 77), and Prairie-Parkland biomes (strata 26-49, and 75-76). From Afton and Anderson (in review).

The U.S. Geological Survey's Northern Prairie Wildlife Research Center hosted a workshop on 9-10 September 1998 to provide biologists the opportunity to share information on scaup and to discuss research needs and opportunities for collaboration. Dr. James K. Ringelman, Ducks Unlimited Inc., was facilitator. Forty-five biologists participated, including biologists from U.S. Geological Survey research centers and cooperative research units; U.S. Fish and Wildlife Service's Office of Migratory Bird Management, Office of Research Coordination, and Alaskan refuges; Environment Canada; Ducks Unlimited's Institute of Wetland and Waterfowl Research; Ducks Unlimited Canada; universities; Long Point Waterfowl and Wetlands Research Fund; and state representatives of the Atlantic, Mississippi, and Central Flyways (see Appendix I).

GIF-Figure 3. Traditional survey strata for the annual Waterfowl Breeding Population and Habitat Survey in North America, with strata classified as in the Tundra, Boreal Forest, or Prairie-Parkland Biome.

Figure 3. Traditional survey strata for the annual Waterfowl Breeding Population and Habitat Survey in North America, with strata classified as in the Tundra, Boreal Forest, or Prairie-Parkland Biome.

Over 2 days, workshop participants reviewed knowledge about greater and lesser scaup, examined potential problems facing the species, identified information and research needs, and formulated a strategy for addressing some of these needs. Accordingly, this report summarizes knowledge of scaup ecology and populations, issues of concern, and recommendations reached by participants, with a complete reporting of recommendations developed by 4 discussion groups. Information from oral presentations and abstracts at the workshop are included in the introductory material (below) and as supportive material for recommendations. The U.S. Geological Survey did not edit the substance of results and recommendations contained herein.


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