This data archive contains data used in analyses of protein sources for egg membranes and whole blood of long-tailed ducks (Clangula hyemalis) and Steller's (Polysticta stelleri), spectacled (Somateria fischeri), and king (Somateria spectabilis) eiders. These data have been published in Miller et al. (2022): Use of marine vs. freshwater proteins for egg-laying and incubation by sea ducks breeding in Arctic tundra (Ecosphere).