Edit (24 January 2013):
Upon seeing more photographs Carlos Gutiérrez Expósito who is as expert in the identification and Ruddy Duck control in Spain commented the following (see also the comment section below):
"Dear friends, thanks for the photos. Definitely and fortunately, the shot belongs to an adult male White-headed Duck. There is no sign of hybridisation and all plumage and bare parts features match perfect with Oxyura leucocephala. White-headed Ducks have two colour morphs. One pale and another one dark. In this case you have one pale bird, because of this it has pale undertail coverts, but not pure white as you find in Ruddy Duck and hybrids. Body shape, body colour (chestnut, not reddish), very white head and blue swollen bill, all match with White-headed Duck. And if you get a detailed view of the bill base, you will see that the profile of the bill base (limit with plumed face) is inverted S shaped. This feature is always like an inverted C in Ruddy Ducks, and mixed in hybrids.
I'm very happy to see that you are in alert with this very serious conservation problem for the western population of White-headed Ducks.
All the best
Thanks to Carlos Gutiérrez Expósito for his comments and thanks also to Benoît Maire, Jacques Franchimont and Diego Jeréz for their comments.
The original blog-post as it is:
My friend Abdelhak Elbanak photographed this stiff-tailed duck earlier this month at the lake of Sidi Boughaba which he originally identified as a Ruddy Duck (Oxyura jamaicensis). But upon looking at the photo more closely, I think it’s rather a male Ruddy Duck (Oxyura jamaicensis) X White headed Duck (Oxyura leucocephala) hybrid. This bird has different characteristics that can be found in one species or the other and here I list the most important:
- Bill is relatively large with slightly swollen culmen at the base, this must have been inherited from a White headed Duck parent (the bill of Ruddy Duck is much thinner and not swollen).
- Head is almost all white except a narrow black area on the crown, the white is so extensive that reaches the neck, this also must have been inherited from a White headed Duck parent (in Ruddy Duck, the white is not very extensive while the black on the head is very extensive in all plumages and extends to the neck and eyes).
- Body colour (bright chestnut) must have been inherited from a Ruddy Duck parent.
- White undertail coverts also inherited from a Ruddy Duck parent.
What do you think? I am happy to be corrected if I have missed anything. Thanks.
It should be noted that hybridisation between these two stiff-tailed ducks may cause conservation concerns for the thriving Moroccan White headed Duck population. In recent years, it’s not uncommon to see tens or hundreds White headed Ducks all year round in some sites like Sidi Boughaba and Douyet. Just check the observations entered into Observado to have an idea about the population, some of these birds are wintering but many are also breeding.