Modeling Populations of Spectacled Eiders

The spectacled eider population on the Yukon-Kuskokwim Delta (Y-K Delta) in western Alaska declined rapidly through the 1980's (Stehn et al. 1993), and was listed as threatened worldwide by the U. S. Fish and Wildlife Service (USFWS) in 1993 (Federal Register 1993). There is a total of between 200,000 and 300,000 spectacled eiders in the world population, but less than 10% of them breed in North America. In North America, about 5000 pairs nest on the North Slope of Alaska and about 2000 breeding pairs nest on the Y-K Delta. The remainder of the world population breeds in Arctic Russia. The entire world population, males and females, appears to winter in a relatively small region of the north central Bering Sea.

The population on the Y-K Delta, about which we have the most information, has been declining for at least 20 years at a rate of approximately 9% per year. The population on the North Slope may also be declining at a slower rate. We do not know the status of spectacled eider populations in Arctic Russia.

The Spectacled Eider Recovery Plan developed by the Recovery Team and published by the USFWS in 1996 describes the status of the population, identifies important information needs, suggests causes for the decline in the Y-K Delta population, and recommends possible management actions. Recent studies have focused on the Y-K Delta population of spectacled eiders because it appears to be declining so rapidly.

Scientists from the Alaska Science Center - Biological Science Office (ASC-BSO) and the USFWS have been studying key demographic parameters of spectacled eider populations since 1991. The Recovery Team identified low adult female survival as the likely cause of the population decline. However, estimates of adult female survival and many other demographic parameters were unavailable at the time the plan was developed. Recent research has focused on post breeding movements, nesting ecology, brood rearing ecology, and the survival of ducklings and adult females.

Studies of postbreeding movements using transmitters tracked via satellites have for the first time revealed the areas in the north central Bering Sea used in winter by spectacled eiders from the U.S. and Russia.
Studies of nest success have demonstrated large annual variation, and the relative importance of avian nest predators.
Studies of duckling survival, in radio-marked broods like the one pictured above demonstrate little variation in annual survival rates, but relatively good production.
Studies of lead exposure indicates that in some areas over 30% of the breeding population experience lead poisoning caused by ingesting spent lead shot. The x-ray image at the left reveals a lead shot in the gizzard of a female eider captured from a nest on the lower Kashunuk River study area.
Studies of adult female survival using females wearing colored nasal disks, like the female in the brood photo indicate that over 78% survive breeding and the harsh, Bering Sea winters each year. However, only 44% of females that ingest lead shot survive to return and nest the following year. Thus, in areas where lead exposure rates are high average survival rates are relatively low.

On the Y-K Delta, nesting spectacled eiders are patchily distributed across the central coast within 15 km of the Bering Sea. This area is without doubt one of the most important in the world for waterfowl production. Two relatively large concentrations of spectacled eiders (>100 nesting females) occur at Kigigak Island and the lower Kashunuk River (Hock Slough). Since 1991, research by ASC-BSO and USFWS focused on these key breeding areas. The programs of intensive research on marked populations provided a vast amount of information on spectacled eiders and several other species of waterfowl breeding in the Y-K Delta.

In recent years, the research program has expanded to include other parts of the Y-K Delta, the North Slope of Alaska, wintering areas in the Bering Sea, and the Indigirka River Delta in Siberia.

In a collaborative effort with the American Museum of Natural History and U. S. Fish and Wildlife Service, ASC-BSO biologists synthesized the results of these studies using a population model. The model, in its most basic form, has been developed into a stand-alone program, SPEI Model, for use by researchers, educators, and managers interested in the factors that influence the growth rate of spectacled eiders populations.

screen shot of the speimod program The user provides estimates of demographic parameters such as the size of the nesting population, breeding propensity, nest success, duckling survival, clutch size, and adult survival. The program uses those values to calculate the expected population growth rate and project the size of the population for 50 years. In addition to demonstrating the effects of variation in demographic parameters, the program simulates the effects of lead poisoning and manipulations of the population (i.e., the addition or removal of nests or breeding females) on population size and growth. The program also introduces the effects of environmental variation (stochasticity) on animal populations. It is not intended as a tool for research, but as a tool to be used by managers and students exploring the relative influence of factors affecting spectacled eider populations. The algorithms in the program are based on a standard pre-breeding census, birth pulse, stage projection (Leslie matrix) model.

The tutorial parameter sets provided with SPEI Model demonstrate the relative importance of each of the demographic parameters on the growth rate of spectacled eider populations. The structure of the program makes it easy to create, edit, and save new or existing parameter sets. The graphic output illustrates changes in population size, population growth rate, and potential problems with population viability.

Federal Register. 1993. Final rule to list the Spectacled Eider as threatened. 58:27474-27480.

Flint, P. L., and J. B. Grand. 1997. Survival of spectacled eider adult females and ducklings during brood rearing. Journal of Wildlife Management 61:218-222.

_____, M. R. Petersen, and J. B. Grand. 1997. Exposure of spectacled eiders and other diving duck to lead in western Alaska. Canadian Journal of Zoology 75:439-443.

Franson, J. C. 1986. Immunosuppressive effects of lead. Pages 106-109 in J. S. Feierabend and A. B. Russell, eds. Proceedings of the symposium on lead poisoning in wild waterfowl - a workshop. National Wildlife Federation, Washington, D. C.

_____, M. R. Petersen, C. U. Meteyer, and M. R. Smith. 1995. Lead poisoning of spectacled eiders (Somateria fischeri) and of a common eider (Somateria mollissima) in Alaska. Journal of Wildlife Diseases 31:268-371.

Grand, J. B., and P. L. Flint. 1997. Productivity of nesting spectacled eiders on the lower Kashunuk River, Alaska. Condor 99:926-932.

Petersen, M. R., D. C. Douglas, and D. M. Mulcahy. 1995. Use of implanted satellite transmitters to locate spectacled eiders at-sea. Condor 97:276-278.

Stehn, R. A., C. P. Dau, B. Conant, and W. I. Butler Jr. 1993. Decline of Spectacled Eiders nesting in Western Alaska. Arctic 46:264-277.

U. S. Fish and Wildlife Service. 1996. Spectacled eider recovery plan. Anchorage, AK.