When studying the images of Common Goldeneye Bucephala clangula taken at Holmestrand harbour it was possible to separate adult females from a second year female and a second year male by head pattern. Most bird guides refer to plumage differences in the wing coverts to age female plumaged individuals, which may be difficult to observe in the field.
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| Adult female: Typical round head form, bright eye and dark bill with yellow tip |
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| Second year female: Smaller slightly less rounded head, dark eye and dark bill with paler tip. |
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Second year male: Pointed head shape, dark eye and all dark bill.
In addition, some paler feathers beginning to appear behind bill
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| Adult male. |
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