I just want to get back to Anja's vulture pics.
IMHO they are all Afr White-backed Vultures.
As we all know, distinguishing AWV from Cape Griffon is difficult. Size is a good feature but only to the experienced observer, or when a direct comparison can be made.
Below follow some features which I use to help me identify the standing bird:
The adult CG's yellow eye and the adult AWV's white rump are about the only clinchers - that is if you manage to see them...
...The colour of the bare skin patches at the base of the neck is not a good diagnostic feature, and can be blue in both CG and AWV.
Thanks for that TG. This is just about verbatim my feeling regarding the ID difficulties these two birds present.
Furthermore TG wrote:
The statement in the SASOL Birds of SA field guide indicating that the bare patches of blue skin at the base of the neck in the adult CG are diagnostic, is incorrect.
I have wondered about that bit as none of the other fieldguides or Roberts VII says different - they just omit to commit! (Refuting mistakes in other fieldguides, on the other hand, is not their function
To add another factor that further confuses the issue - in a feature article Refining our vulture culture
published April 2004 in Science in Africa, the Vulture Man, dr Gerhard Verdoorn wrote:
Three other griffon vultures are found in Africa - the Eurasian Griffon Gyps fulvus, Rüppell's Griffon Gyps rueppellii, and the African White-backed Griffon Gyps africanus. These griffon vultures are very closely related to each other and interbreeding between Rüppell's Griffon and the Cape Griffon has been recorded in South Africa. There is strong phylogenetic evidence that Cape Griffons have interbred with African White-backed Griffons in Namibia.
This gives credence to the suggestion that ID of these birds should be kept simple and along the (fool)proven
methodologies. Once one gets too sophisticated too soon you are bound to make mistakes.
Unless you are a subject expert, the only ID-features you should consider are as per an earlier post:
Number 1 (best feature by FAR) - dark-eyed birds are WB while golden-eyed ones are Cape.
Number 2 - Where this can be seen, a white rump = WB; uniform-coloured rump and back (pale brown) = Cape
I hesitate with Number 3 - Uniformly brown flight feathers = WB; spotted upper-wing coverts (black, ad.; white, juv) = Cape. My hesitation is due to this being a much simplified "rule" and if the (even experienced) observer is not careful, it too can lead to confusion.
As TG wrote:
correctly aging a bird is important in this regard.
When it comes to using the plumage coloration of these birds as an ID-feature: if you do not understand or know the stages they go through as they age, rather leave it alone.
All other differences often stated (differences in size, downiness and length of neck, length, thickness and colour of neck, colours of the crop patch or the "robot" patches) are too subjective and prone to variation that I do not subscribe to using it.
This is the guideline as I employ it in my own birding of vultures. I am chuffed to find other more experienced birders enjoying much higher regard suggesting the same rules for safe and sure identification of these birds.