Decline in a Population of Spectacled Eiders Nesting on the Yukon-Kuskokwim Delta, Alaska

Abstract

The number of spectacled eiders (Somateria fischeri) nesting on two study areas near the Kashunuk River, on the central Yukon-Kuskokwim (Y-K) Delta, Alaska, declined by over 75% in the last 20 years. Nesting densities have remained low, but have not significantly declined since 1985. There has been no decrease in the reproductive effort of individual females as indicated by average clutch sizes. There has been a significant decline in the proportion of nests located on islands on one of the two study areas. Nesting success declined significantly during the 1970's. Success was not monitored in recent years, but has likely been low, based on the poor nesting success and declining numbers of cackling Canada geese (Branta canadensis minima) and black brant (B. bernicla nigricans) nesting on the area. Nest predation by arctic foxes (Alopex lagopus) severely limited the productivity of cackling Canada geese, and foxes were likely the major predators of eider nests. Persistent high predation rates may lead to local extirpation in highly philopatric species such as eiders. The spectacled eider (Somateria fischeri) breeds along the coasts of the Bering and Chukchi seas in western and northern Alaska, and northern and eastern Russia (Bellrose 1980). The population on the Yukon-Kuskokwim (Y-K) Delta is in decline (Stehn et al. 1993), and is listed by the U. S. Fish and Wildlife Service (1993) as a threatened species. Evidence for the decline is based on changes in the number of eiders counted during aerial surveys, and current estimates of nesting density (Stehn et al. 1993), relative to an extrapolated estimate derived from the number of eiders nesting on small study sites on the Y-K Delta in the early 1970's (Dau and Kistchinski 1977). Here we present evidence of a long-term decline in the number of nesting eiders based on changes in the number of birds on two study sites monitored for up to 20 years. STUDY AREA AND METHODS The study areas were located in the Yukon Delta National Wildlife Refuge, along the Kashunuk River on the central Y-K Delta, Alaska (61°26'N, 165°27'W), approximately 20 km upriver from the Bering Sea (Fig. 1). Habitat at the sites is described in detail elsewhere (Ely and Raveling 1984, Babcock and Ely 1994). Both study areas were covered with numerous small lakes, ponds, and tidal sloughs and dominated by moist tundra vegetation (mixed sedges and grasses) interspersed with intermediate and upland dry tundra (lichens, mosses, and dwarf shrubs). Portions of the Old Chevak study site were slightly higher in elevation and more inland than the Onumtuk site, and were characterized by more intermediate and upland habitat. Habitat used by nesting spectacled eiders on the Y-K Delta lies within an estimated 9300 km2 of wet sedge/grass meadows categorized as the vegetated intertidal zone (King and Dau 1981). This zone is essentially the lowland terrain between the outer edge of vascular plant growth (i.e. normal high tide line) and the maximum inland extent of storm surges identified by the driftwood line. All of the Onumtuk area, and the southern and eastern portions of the Old Chevak area were within this vegetated intertidal zone. Eider work on the 11.1-km2 Onumtuk study area began in 1969 (Mickelson 1975), and was continued through 1973 (Dau 1974). In 1975, two 2.8-km2 sites were selected within the original study area. Investigations at these plots were conducted by CPD untiI 1980; refuge biologists lead research activities there untiI 1985, when CRE took over the work. The 12-km2 Old Chevak study site is adjacent to the Kashunuk River just north of the Onumtuk plots. The Old Chevak plots were initially searched in 1977 and 1978, when CRE was conducting work on nesting geese (Ely and Raveling 1984). Field methods used here were exactly the same during all years. Although we did