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.
Other examples of progressive greying
This Blue-naped Mousebird (Urocolius macrourus) photographed in southern Algeria is also affected by progressive greying according to Hein van Grouw (see his comment in the update in the middle of the page).
Some birds compiled in this page about ‘leucistic birds found in Northwest Africa’ might have been affected by progressive greying as well. Comments welcome!