Breeding Stress of Female Eiders in Maine

Abstract

Physiological condition of breeding female American eiders (Somateria mollissima dresseri) was studied on islands in Penobscot Bay, Maine, from 1973 to 1975. Of particular interest was the hypothesis that stresses associated with reproduction predispose eiders to increased mortality and lowered productivity. Females established large nutrient reservws prior to egg laying and essentially terminated feeding before laying. They relied heavily on nutrient reserves for formation of eggs. Wet weights of the gizzard, liver, and intestine decreased significantly during follicular development before and during laying. There was no correlation between body weight and clutch size after egg laying, suggest:ng that clutch size was determined by size of nutrient reserves. Females fed little or not at all during incubation and lost 32 percent of their post-laying weight. Wet weights of the pectoral muscle decreased significantly. Based on fat and protein levels, most females probably could not continue to incubate when body weights approached 1.10 kg. Hematocrit percentages and levels of total plasma protein and free fatty acids were physiological parameters that indicated degenerative changes in incubating eiders. Levels of non-protein nitrogen in the blood plasma appeared to be considerably depressed but did not change during incubation. The renesting ability of American eiders appeared limited, at least in part, by the dysfunction of the digestive tract concomitant with egg laying. The digestive tract was so altered that even when a clutch was lost after only a few days of incubation, females required many days to reestablish