Clutch, egg and body size variation among common eiders breeding in HudsonBay, Canada

The Hudson Bay common elder (Somateria molissima sedentaria)-is a unique su bspecies of elder that remains within the confines of Hudson Bay throughout the year. We compared clutch, egg and body size variation among population s of common elders breeding in eastern and western Hudson Bay. Clutch size did not differ substantially among these populations. All elders in Hudson Bay laid larger clutches than other subspecies in eastern North America. As Hudson Bay common elders do not undergo extensive migrations, they may hav e more energy reserves available to them for egg production. Elders nesting in eastern Hudson Bay laid larger eggs than elders nesting in western Huds on Bay. Further, elders in eastern Hudson Bay tended to be structurally lar ger, but had smaller bill processes. These differences may have a genetic b asis. Smaller egg size and body size may arise in western Hudson Bay from m ixing with the smaller borealis subspecies nesting to the north. Further wo rk to resolve genetic affinities, determine levels of male and female dispe rsal, and examine variation in reproductive ecology are needed to resolve t he sources of these differences.