A Black-necked Grebe (Podiceps nigricollis) affected by progressive greying photographed at Dayet Aoua in the Middle Atlas Mountains by Saad Rih. (It’s not a leucistc bird as stated before, see the comment in the update below).
Un Grèbe à cou noir touché par le ‘grisonnement progressive’ photographié à Dayet Aoua dans le Moyen Atlas par Saad Rih. (Ce n’est pas un oiseau leucistique comme indiqué précédemment, voir le commentaire dans la mise à jour ci-dessous).
We received the following comment by email from André Konter, a specialist in grebes and the author of Grebes of our World, published by Lynx Edicions in 2001:
Tom Conzemius informed me about the above record. I can confirm that this is not a leucistic grebe, but a grebe affected by progressive greying. It is a common mistake to confuse the genetically caused leucism and the age related progressive greying.
I have read the article by van Grouw (2006) which does not cite progressive greying. But thanks to André Konter’s comment above, I have found a second article by the same author (van Grouw 2013) which discusses the progressive greying (with examples) and the confusion it creates when distinguishing it from other colour aberrations like leucism. I have also found a comment by Konter himself about the grebes specifically. Here they are:
- van Grouw, H. 2006. Not every white bird is an albino: sense and nonsense about colour aberrations in birds. Dutch Birding 28: 79–89.
- van Grouw, H. 2013. What colour is that? The causes and recognition of common colour aberrations in birds. British Birds 106: 17–29.
- Konter, A. 2014. Misidentification of genetic colour aberrations – not every white grebe is an albino. Musée national d’histoire naturelle, Luxembourg.
Many thanks to André Konter for the comment and to Tom Conzemius for forwarding this observation to him.