Cygnus columbianus · Whistling Swan
|datum||1 t/m 27 december 1990: 27 dagen|
|status||Niet aanvaard, gepubliceerd in jaarverslag CDNA|
|opmerkingen||@ (photographed; amount of yellow on bill was considered too extensive to exclude Bewick's Swan C c bewickii; cf van der Burg et al 1991). Based on newly described identification features other than the amount of black on the bill (Visscher & van Duivendijk 2015), all five records were reassessed. According to Evans & Sladen (1980), only a small minority (4.3%) show more than 10% yellow on the bill. This minority type however seems to be over-represented in Dutch records. This was, eg, the case for a widely twitched bird in Drenthe, Friesland and Groningen in the winters of 1997/98 and 1998/99. ‘Hybrigades’ with Bewick’s Swan C bewickii are a realistic option, and Bewick’s with aberrant bills are not unheard of (Evans & Sladen 1980). Identification based on a single feature is therefore tricky, especially in birds with a relatively large amount of yellow on the bill. The presence of the new features could not be determined in the records. It was therefore decided that all records are no longer proven and, as a consequence, Whistling Swan was removed from the Dutch list. Annual Report 2018.|
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