SLAGBOOM TH (1987) Short contributions: Observation of a Cygnus columbianus with almost black bill. LIMOSA 60 (1): 40-40.

Bewick's Swan Cygnus bewickii On 7 and 15 February 1980, a swan was seen in the polder Arkemheen (Gelderland) with an almost entirely black bill (fig. 1), matching the characteristics of a Whistling Swan Cygnus columbianus columbianus. However, the possibility that the bird was a melanistic Bewick's Swan Cygnus columbianus bewickii cannot be ruled out.

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