SWENNEN C (1990) Short contributions: Common Eiders Somateria mollissima with aberrant plumages.. LIMOSA 63 (3): 112-114.

Two types of aberrant plumages were recently discovered in Common Eiders Somateria mollissima in the Dutch Wadden Sea. The wings of both types resemble juvenile wings, with some scattered white coverts. The first type looks in front (head and breast) like an adult male Eider in breeding plumage, the rest of the body is dark as in eclips plumage. Since 1977, when one such bird was discovered, up to seven individuals have been seen yearly. The second form looks like a firstwinter male, but with white feathers occurring on the head up to above the eyes. Since 1987, a few living birds have been seen and five dead ones. The second type appeared to be adult females with atrophied ovaries in spite of their male-like plumages. The first type is supposed to represent sterile adult males. Both types of aberrant plumages may be caused by a disorder in the hormonal balance, either by age or by chemical contamination.

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