Understanding the ecological and evolutionary forces which influence the abundance and diversity of biological resources is important for effective management and conservation. In the absence of important ecological data on movements and breeding ecology, molecular genetic markers can provide critical empirical sources of data. Results from studies of the threatened spectacled eider (Somateria fischeri) are described based on molecular markers with different patterns of inheritance. Maternally inherited mitochondrial (mt)DNA, bi-parentally inherited microsatellites, and a sex-linked (Z-specific) locus were used to document the extent of genetic differentiation within and among the three major nesting areas for the species (Russia, Yukon-Kuskokwim Delta, Alaska, and the North Slope of Alaska). Results from contemporary populations are compared with data obtained from museum specimens collected over the period 1860-1960 from the same locales.